"AC" style HVAC box conversion to manual controls

[Dr.Jeff]

EDIT: Note that I am correcting or adding information to this thread. I will try to highlight those changes.

I have a '79 X (1500 5-speed) with factory air conditioning. This thread is not about rebuilding or restoring the system; others like @LarryC have already done a supreme job of documenting that. My intent is about making the AC system more to my personal preference by doing some modifications to it - such as changing how it is operated by the dash controls. I credit @Rodger for motivating me to try this, similar to some mods he made using a "add-on" aftermarket AC system. This will be presented in a few sections as I progress through the project.

The whole HVAC system is very different with "AC" vs a non-AC model. Here's diagrams of both systems:

The two boxes are configured differently and the internal airflow is directed differently. One advantage with the AC version is the two outermost air vents on the dash are actually connected to the HVAC box. Aside from that the general functions are similar - with the AC box adding the AC option - but they are laid out quite differently and therefore have many components that are not interchangeable.

For example the heater core (#19 on the diagram) is different, as discussed in this thread: https://xwebforums.com/forum/index.php?threads/ac-equipped-x1-9-heater-core.40503/#post-373131. My core leaks so I need to either repair or replace it.

Another difference is the blower assembly is a "squirrel cage" style rather than a "fan blade" one. Another forum member is looking into a suitable replacement for the blower motor on the AC style (#30 on the diagram). Fortunately mine is working fine.

Yet another major difference is the controls for the HVAC system; on the AC version they are vacuum operated (not shown on the diagram) vs the manual levers/cables on a non-AC system (#6 on that diagram). I've found this vacuum control setup to be rather problematic. For one thing they tend to get "vacuum" leaks from multiple points, plus the vacuum solenoids that actuate the "flapper doors" (air circulation control) seem to have a limited operation. As a result I find the airflow through the box isn't well controlled and therefore the system does not function well. Furthermore the operation of the "push button" control panel is a bit finicky and can be prone to breaking. Here is the main vacuum control mechanism:

As you can see it has a combination of vacuum and electrical connections. Pushing "in" any of the control buttons causes the others to pop back up so only one function operates at a time. The buttons actually slide into the unit to activate various vacuum and electrical circuits internally. More on that in a minute. This replaces most of the cables and levers on a non-AC control panel.

Due in part to the typical problems with most vacuum operated systems (e.g. leaks), and in part to the fact this engine is getting a turbo (positive manifold pressure rather than vacuum), I've decided to convert my AC controls from vacuum operated to the manual "cable" operated one as used on the non-AC system. I find the cable system to be much more positive feeling in use, offers better control of the HVAC functions, is more reliable (although it also has its own potential issues), and looks more suited to the interior style of the X. To accomplish this conversion I will need to replace entire control mechanism; the selector panel, solenoids, wiring, etc., between the two systems (AC and non-AC). Fortunately it is a fairly easy job, as many of the components that need to be replaced are a direct fit between them.

Beginning with the control panel. The vacuum control unit (pictured above) fits onto a "framework" that is mounted basically the same as that for the non-AC system. This allows both systems to be installed in the dashboard the same way:

Therefore the "framework" for the two control mechanisms can be interchanged. Like the non-AC system, this mechanism is held by a surround that fits into the dash. Both systems use the same surround. The face plates are different to correspond with the "push button" vs "lever" controls, but they are interchangeable. Here is the surround with the non-AC faceplate:

There is one "lever" control on the bottom of the AC version to operate the heater valve (ignore the green arrow and yellow box for now):

That lever is pretty much the same as on the non-AC system. So converting the heater valve control is simple, just use the existing one. The valve is located differently on the AC box so they have different length cables. But the original cable connects to the control lever in the same way (green arrow above).

The two additional control levers from the non-AC system will need to be added. Since both control mechanisms fit the same it is easy to swap the non-AC mechanism with its levers as a complete unit (ignore the markings for now):

The AC system has a three speed blower vs the two speed one on the non-AC system. Therefore the control switch for the blower is different, but they are also interchangeable. So simply swap the switch (yellow boxes in the above pics) - they install with two screws. This allows the original wire harness for the blower to remain as it is.

The cables that attach to this mechanism's levers (blue arrows above) operate two air doors ("flappers") on the non-AC box. One allows air to be directed up to the defrost vents. The other moves the main door at the top of the box to allow fresh air in from outside the vehicle. On the AC style box there are three doors, but two of them are inter-connected and move together (see #11, 12, 13 on the "AC diagram"). The reason for this is it provides a "recirculation" function for airflow (which can be used for both AC and heat). So effectively it has two doors as on the non-AC box. They are located differently and the airflow through the system moves differently, but the resultant functions are similar. Therefore the vacuum solenoids that operate those doors on the AC box can be removed and replaced with the cables from the non-AC box. Luckily the doors have points where the cable ends can easily attach to. Here is an example of the defrost duct and vacuum control solenoid (courtesy of Rodger); the blue arrow is the solenoid that will be removed and the yellow arrow is where the cable connects in its place:

The other door has a similar setup and is converted the same way - remove the solenoid (green arrow) and connect the cable (blue arrow):

Due to the different locations of the doors, the lengths of the cables from the non-AC system may not be [correction- ARE NOT] ideal when used on the AC box. I haven't reinstalled it yet to find out. [I just tried installing everything and found the cables need some alterations]. But the AC box even has the little provisions to anchor the cable sheaths, as if it was initially designed to be cable operated. [Correction- the AC box has some provisions that can be used to anchor some of the control cables, but others need to be added. I will make further comments about the cables in a later post]

Now the control mechanism has been converted to manual cable operation, the 3-speed blower control has been retained, the heater valve is working, the HVAC box functions are converted, and everything fits into the car the same way as it was...with one exception, the wire harnesses. At this point I have only sorted out some of the differences between the systems' wires. For example the 3-speed blower motor, as described. Also the two control panels (AC and non-AC) have slightly different illumination, but that is only a matter of swapping the little light bulb holders between them. However there are other differences that I still need to address. If you look back at the pics of the "push button" control unit you see it has a vacuum hose connector and some electrical connectors (red):

The vacuum portion is now completely eliminated, but the wires from those electrical connectors still need to be sorted. Some of it is to activate the AC compressor. The X has a very funky (and inefficient) setup for the electrical portion of the AC system. I am eliminating all of the original AC wiring and utilizing a trinary switch in its place (more on this later). Therefore most or all of these wires at the control panel will also be eliminated. It appears the stock AC controls do not allow for adjustment of the air temp; operating the heater at the same time seems to be the only way to regulate it. I will add a AC temp control rheostat as part of my new AC wiring layout. I think the square hole for the old clock in the controls faceplate will be a good location for it. However at this time the car is gutted for body and paint work and the wire harnesses are wrapped in plastic so I cannot trace everything. This info will have to be added to the thread later.

Something that you may find odd when converting to the manual controls is the display icons on the control mechanism faceplace:

For one, the blower switch now has three speeds but the faceplate only shows two. However the switch itself operates correctly. Another thing is the color of the little "arrows". The lowest lever is for the heater valve and that has a blue arrow. The middle lever now operates the fresh air door and it has a red arrow. To me those two arrows should be opposite colors to correspond better with their functions. But unfortunately you cannot simply swap the positions of the controls, the levers themselves are different and will not work well if used differently. [Correction- I later realized that the non-AC box I have was not assembled correctly by someone in its past. The cables and levers were not in their correct positions. Therefore I was mistaken about the functions and icons on the faceplate. I'll add more on this later]. The top lever is still the defrost control, so that icon appears correct. And there is still the same window for the factory clock to the right. The original clock is horrible in my opinion and will be replaced by something else.

I'm sure I'll think of more general details and come up with more pics to also add later. I will start another post to further discuss the workings of the original vacuum control "push button" panel and why it has so many problems.

EDIT: One thing I forgot to mention is the rest of the vacuum system, beyond the control panel and solenoids at the dash/HVAC box. Naturally the vacuum source is from the engine. A single vac hose goes through the firewall to the spare tire well. I noticed the vac hose was partially smashed as it went through the firewall, which would have reduced the airflow through it. In the spare tire well the line goes into a vacuum canister that serves as a 'extra supply of negative pressure air'. From there another single vac line goes along the floor, on the right side of the center tunnel, in the joint between the floor and tunnel. The main wire harness that carries from the front to rear of the car and one of the AC barrier hoses also travel along the same place. On this '79 the soft vac line was under that large wire harness and AC hose, such that when the factory assembly line secured the harness and hose down they pinched off the vac hose. And I mean it was completely occluded, where no air could pass. So the whole vacuum control panel was inoperable since day one on this car. Thankfully all of that is now gone.

EDIT: The control levers and cables on the non-AC system are arranged with the defrost lever on top, the heater valve lever in the middle, and the fresh air level on the bottom (I had that wrong earlier). When converting the AC system to these manual controls you can connect the cables in the same locations - thereby retaining the correct icons on the faceplate. However the location of the "doors" on the AC box are different, so the two original cables from the non-AC box are too short to use on the AC box (the heater valve can retain the original AC style cable). I purchased some random control cables from the LADA parts supplier for very little money (links below). I will use them with any needed adjustments on this conversion. It is easy to shorten ones that are too long, but obviously not the opposite.

LADA control cables, two options:

Lada Niva 1700 Heating + Ventilation Control Cables Kit

Lada Niva 1700 Heating + Ventilation Control Cables Kit Heating 1700

ladapower.com

I got this one. More on it later.

Lada 21011 2101 2102 1200 1300 Heating + Ventilation Control Cables Kit

Lada 21011 2101 2102 1200 1300 Heating + Ventilation Control Cables Kit Heating

ladapower.com

There may be more options available as well. I purchased one of these two (don't recall which one at the moment). Tomorrow I will dig them out, measure the lengths, and look at the part number to identify which ones I got. You may wish to choose another set, or find some from another Fiat or different car. See the following EDIT for more information on the Lada cables.

EDIT: After more testing different arrangements for the control cables I've come up with what I think will work best. I purchased a kit of new cables from the Lada parts source (linked above). I got the one for a 1700 (the first link). The length of these three cables will work great for my conversion to manual controls, as we will see.

As I stated earlier the AC control panel has one lever, located on the bottom of the mechanism. Normally that operates the "heater valve". On the non-AC control panel there are three levers, also with one located on the bottom, but here it operates a different function...the heater valve is controlled by the middle lever. This means the two cables face in opposite directions as they exit the mechanism (the middle and lower levers have cable attachment points on opposite sides). To maintain the correct icon arrangement on the faceplate you will need to swap the heater cable to the middle lever, but this affects the orientation - aiming to the passenger side vs the drivers side (as it did before). I believe the original AC system heater control cable can still be used but it isn't ideal due to the redirection needed. A longer cable would help. Or you may choose to use different levers on the control mechanism; that will orient the direction of the cables much better, allowing the use of shorter ones. But that will also make the icons on the faceplate wrong. In my case I won't be retaining the original heater valve. I'm using one from a VW, mounting it next to the heater core - like where the non-AC box does. So the original non-AC heater cable would work, although I will use one of the new cables (the middle length in the Lada kit - which is just right for my arrangement).

The cable for the "defrost" control also needs to loop around from the opposite direction. Same reason, the orientation of the control levers is different compared to the location of the "flapper" doors on the two boxes. That makes it rather long to prevent binding. I measure it to be around 35" long. Much longer than any of the stock X cables. Fortunately the longest cable in the Lada kit I bought is the right length.

The third lever (now the bottom one) controls the "recirculation" (or "fresh air") function. As it turns out the distance between the control mechanism lever and the attachment to the "flapper" door (for the recirculation) is very short. The orientation of the control mechanism points the cable directly toward the door, so that cable only needs to be about 10" long. The shortest cable in the Lada kit is longer than this but it can easily be cut down to work.

As you can see that kit of cables from Lada works really well for this conversion. And they are incredibly affordable. Even better, the ends all have the correct "attachment shapes" to connect them to everything. Having all new cables makes the controls work much better. All this makes them a great deal for this project.

It is a bit of a struggle getting the cables in their proper locations, orienting them around everything, and attaching them to their related connections. Just doing trial assembly on the workbench was a bitch, I am not looking forward to doing this in the car. And things may end up changing as a result. But at the moment that's the plan.

 

[Dr.Jeff]

In my last post I showed the vacuum "push button" box that serves as the main HVAC control unit for AC equipped X1/9's. I also mentioned that it, along with many vacuum based components, are prone to leaking - therefore reducing the vacuum level and dimenshing the operation of whatever it serves. I took apart a "push button" box to see what's inside and quickly realized why it is so problematic.

The plastic box has a modular vacuum connection on the back:

As you can see there are three vac lines on it. One is the vacuum source from the engine, the other two go to the two vacuum solenoids on the HVAC box (as described in the original post). The control unit moves the vacuum source between those two solenoids as needed by selecting the function buttons on the front:

On the back of the control unit there are actually seven vacuum ports:

But only three of them are used, the rest are blocked off by the rubber plug:

The back of this control box is held in place by some little plastic tabs or buttons. Here's an example:

These snapped off to allow removal of the rear cover:

As you can see there is no form of seal anywhere inside this box. So air (vacuum) can leak from a number of places. Further disassembly of it reveals a series of "reeds" inside:

These reeds were stacked on top one another inside the box:

Various combinations of them move about when each of the selector buttons (on the face) are pushed in. The buttons just slide back vertical posts inside, one for each button:

The movement of those vertical posts moves the reeds (sliding back and forth as their "ramps" are pushed back) to act on the two "switches" on the rear cover; one is for the vacuum connector (purple) and the other for the electrical connector (yellow):

The movement of these two switches (side to side) open and close contacts inside them:
Electrical...

And vacuum (see the tiny holes that get covered or exposed)...

This is what changes the functions for the HVAC unit; a combination of vacuum lines to solenoids, and electrical connections to the compressor. So the buttons on the face of the unit activate various combinations of movements for the two switches on the back of the unit. But really there are only two things happening; either of two vacuum solenoids is opened/closed, and the compressor is turned on/off. This whole control box design seems a bit complicated for such a simple task. And you can see by the internal bits why it is prone to air leaks and/or breakage. This is why I opted to eliminate it completely and revert to simple manual lever/cable controls for heat and airflow control, with a standard electrical switch for compressor control.

 

[Dr.Jeff]

Now that the operation of the "push button" control panel is understood, and the vacuum solenoids for the HVAC box are replaced, I need to figure out exactly what the electrical connections on the back of the control box are.

As I mentioned previously the X's AC system has a very complex array of temp switches, pressure switches, wires, solenoids, relays, etc, to control the compressor clutch's electrical on/off function. It is intended to prevent freezing in the system (unlikely with this antiquated design) while the compressor is running. This also controls the cooling fan added to the radiator. I imagine the electrical leads on the back of the control panel are just a part of all this, and will be eliminated when I get everything rewired (more on this in the next paragraph). But as I explained I cannot verify that until I again have full access to all the wire harnesses.

By utilizing a trinary switch the compressor and cooling fan are controlled very simply using a pressure based design. It is commonly mounted on the receiver/dryer:

This allows the removal of all the stock AC electrical components and wires. Creating a much simpler setup that works much more efficiently. However as far as I can tell the X's AC doesn't have any real means of controlling the interior (cockpit) temp. It either runs at full capacity or none. Perhaps that is why they have all of those "freeze-up" detection devices. The interior temp could be regulated by simultaneously running the AC and the heater together, as many modern cars do. But on any old car with all of their inherent characteristics and basic controls this doesn't work as well as it does on a modern car. Therefore a better method of controlling the temperature is also needed.

Fortunately this is also very easy to do. A rheostat connected to a temp sensor can be included with the compressor wiring to cycle it on and off, thereby regulating the cabin temperature. These are common and simple units that require very little to install. It looks like this:

They come in a selection of styles. The temp probe is placed on the evaporator core to read the cold air temperature. There are a pair of electrical contacts on the back. This opens or closes the electrical circuit to the compressor. By adjusting the control it will cycle the compressor on and off to maintain the desired cabin temperature. It also acts as a safety backup in the case of a freeze up. These can be had with a rotary knob (as the one shown has), a slider switch, electronic, or other forms of operator control. They usually also include a "off" position to completely shut down the AC system when not needed. So as far as wiring goes, there will be one lead coming into this device and going back out of it to the circuit with the trinary switch (and compressor relay). If desired the blower fan switch can also be spliced into this circuit, to prevent the compressor from running without the blower working. That one lead should eliminate all of that other wiring at the back of the "push button" control panel.

A control like this can be mounted anywhere on the dash to adjust the AC temp. I'm thinking I'll use the space where the original clock was. With a blanking panel over the square hole and a rotary knob on the face of it. There it will be within the HVAC control panel faceplate along with all of the other HVAC controls. Selecting the right style knob will help make it fit into the overall aesthetics of my dash.

Here is one representation on how the whole system is wired:

This should conclude the conversion of the AC system to manual controls. And significantly improve its function in the process.

 

[Rodger]

Awesome write up and great explanation of the stock system!

 

[kmead]

Thiis has been what I have been thinking through for my ‘87 which has AC. I hate the vacuum control system and the electrical control system has always seemed too complex with little to show for it.

On mine the plan is to adjust the IP akin to Hussien’s compression of the instruments down and forwards, install a modern Carplay type system where the AC and stereo goes today and move the HVAC control system as a manual solution into a center console akin to an early X type solution in front of the shifter. I have looked at the original Miata control head as an alternative but have abandoned that approach, though I do like its integral fan and AC on switch.

Excellent thread and great work.

 

[Dr.Jeff]

move the HVAC control system as a manual solution into a center console akin to an early X type solution in front of the shifter.

Since the control cables need to be longer than they were on the non-AC box anyway, then it would be easy to make them any length to accommodate locating the controls almost anywhere. I thought about utilizing the early style heater controls (on the console) because I really like the classic look of them. But I don't have access to the parts, and I really need to start streamlining my projects. So I decided against adding more to the project. But that would look great:

However your comments are making me think about swapping the position of the HVAC control panel with the opening for a radio (I think that's what you were referring to with Hussien's work?). That is a simpler job retaining the existing framework and surround. I believe Huss was able to just invert the surround to accomplish it? I'll have to look again, but that may also make routing the control cables easier. Due to the different position of the "flapper doors" on the AC box, one of the cables needs to make a 180 degree bend, then another 90 degree bend in a fairly short distance. It would be nice to lengthen that, which lowering the control panel may(?) accomplish. I plan to use the radio opening for extra gauges, sort of like this:

So inverting the position of them and the HVAC controls will work.

 

[Dr.Jeff]

Regarding the electrical portion of the stock AC controls, go back to post #2 where I examined the internal components of the vacuum "push button" control module. You will recall there was a switch on the rear cover with three wire contacts, plus two more connectors coming off the inside of the unit:

After tracing the movements of those "reeds" (by way of the push buttons) and how they position the switch in each setting, plus tracing the internal circuits for the other two contacts, I was able to figure out how the control unit operates electrically.

Here is the wire diagram for the AC system. The red circle is the control module we are discussing:

You can see the same three contacts on one side and two more on the other side, as I just described coming off the back of the unit. If you trace those leads to their respective components, then follow the circuits as each of the "push buttons" is activated, you see what's happening. Frankly it is overly complex but does very little. The "Cliff Notes" version is the AC compressor is turned on when the "AC" or "MAX AC" buttons are selected (by way of the compressor relay and all the other sensors/switches/ etc). Also the second cooling fan on the radiator is activated when the compressor is on (by way of another relay). Finally the blower motor is switched to "low" when certain functions (AC and max AC) are selected, (also by way of the relay and other components). NOTE: I find it odd that "max AC" would trigger the blower to "low" speed. All vehicles that I know of put the blower on "high" for "max AC". Unless the Fiat wire diagram is wrong. Since my Ac wasn't working prior to this project I don't know exactly how it functions in reality. Anyone?

So none of the electrical portion of the control unit has anything to do with directing the airflow (from the HVAC box) - that is handled by the vacuum solenoids, or adjusting the AC air temperature - there isn't any adjustment for that, or any other functions. It really does little more than switch on the compressor. If you look back at the electrical diagram I showed in post #3, it will do all of this and much more with only a few simple wires:

And even some of this is not necessary, like a manual override switch for the fan, or the temp sensor for the fan (already exists on the radiator).

Therefore by converting the control unit to the levers and cables, then adding a temperature control (as described in post #3), everything is easily controlled by the driver with those levers, a single switch (knob), and selecting the desired blower speed accordingly. Pretty much the same as the non-AC heater/vent controls, but now with the AC option.

I think this concludes my research and development portion of the project. The final step will be reinstalling everything once the car is ready for it.

 

[darwoodious]

Wow, you've been thinking about this @Dr.Jeff. For my project, I've decided to punt on A/C for now and finish the damn thing first. Later, if I get motivated, I can add A/C as I have the aforementioned A/C heater assembly unit diagram you've shown. I also have an early A/C center console but it is not to my liking - I would personally prefer a simpler setup that looks like the nice simple non-AC setup of the early cars. LIke this:

My plan, if I ever do get around to it, is to modify that top lighted "close for max def" into a toggle push button with a white (AC off) and blue (AC on) backlight. Next, the heat selector stops being a mechanical valve control and instead controls an arm that feeds into a variable impedance controller that is fed into some simple computer (like an Arduino). Essentially you the driver are telling the dumb computer "I want this heat". An electrically controlled actuator on the heater valve as well as one for the expansion valve should allow the crappy Arduino to produce the heat needed. Options to improve the system include observing the current tamp based on a couple of factors like ambient temp (heater box intake near the top), interior temp whatever. I'd probably go for the simpler setup. Unsure at this point.

Getting rid of all that vacuum crap is easy these days with cheap computing. Similar to the way fuel injection made carburetors extinct. The goal is to make the interface simple regardless of the interface you are copying (early X vs. late X).

So I'll be keeping my early A/C box for the possible future where I want to add it. Love this post. Good to see your thinking!

PS: my primary distain for adding A/C to an X is based on how cramped the cabin is and how much crap is involved in doing all of this. Also, I live in Seattle and when I travel I only go as far as SoCal south, Montana east and maybe Utah southeast. Maybe Calgary when the borders open up again. I understand others don't have the beautifully temperate weather we have here.

 

[bjwhite]

You had me until you said the original Vegliaflash was terrible and would be replaced with something else.

I've always loved the Vegliaflash clock in these cars. It's part of what makes them special. Also had one in the Beta. I also love how they can be changed from 12h time to 24h time and back by soldering or cutting a soldered joint depending on which you want. Obviously, 24h time is best so.

 

[Dr.Jeff]

Wow, you've been thinking about this @Dr.Jeff. For my project, I've decided to punt on A/C for now and finish the damn thing first. Later, if I get motivated, I can add A/C as I have the aforementioned A/C heater assembly unit diagram you've shown. I also have an early A/C center console but it is not to my liking - I would personally prefer a simpler setup that looks like the nice simple non-AC setup of the early cars. LIke this:
View attachment 47004

My plan, if I ever do get around to it, is to modify that top lighted "close for max def" into a toggle push button with a white (AC off) and blue (AC on) backlight. Next, the heat selector stops being a mechanical valve control and instead controls an arm that feeds into a variable impedance controller that is fed into some simple computer (like an Arduino). Essentially you the driver are telling the dumb computer "I want this heat". An electrically controlled actuator on the heater valve as well as one for the expansion valve should allow the crappy Arduino to produce the heat needed. Options to improve the system include observing the current tamp based on a couple of factors like ambient temp (heater box intake near the top), interior temp whatever. I'd probably go for the simpler setup. Unsure at this point.

Getting rid of all that vacuum crap is easy these days with cheap computing. Similar to the way fuel injection made carburetors extinct. The goal is to make the interface simple regardless of the interface you are copying (early X vs. late X).

So I'll be keeping my early A/C box for the possible future where I want to add it. Love this post. Good to see your thinking!

PS: my primary distain for adding A/C to an X is based on how cramped the cabin is and how much crap is involved in doing all of this. Also, I live in Seattle and when I travel I only go as far as SoCal south, Montana east and maybe Utah southeast. Maybe Calgary when the borders open up again. I understand others don't have the beautifully temperate weather we have here.

Darin, thanks for the kind words. This X was already a AC car, so really all I'm doing here is converting the controls from vacuum to manual. The vacuum controls on mine leaked so badly they really did not work. Due to my current location in a desert region AC is not an option, so I have to refurbish the whole system anyway. And after seeing how the factory did things, I decided it definitely required a lot of changes/upgrades to function better. Which is why I'm going with the optional layout for other components in addition to converting the controls. However if someone has a AC equipped X and wants to keep the system stock, but convert the controls from vacuum to manual, that can be done with what I described in the earlier portion of this thread. Basically the only wire they need to reuse from the control unit is the "green and white" one. That triggers the AC relay. So connecting it to either a simple switch or the temperature control (pic below) could make everything work.

That early style console mounted heater control panel you showed is the one I was thinking of:

I like the vintage styling of it, and locating the controls in the center console would be classic. I'd also start with the basic "heater" (non-AC) version, but retain the cables...just like I'm doing now. Those three levers can be used in the same way as on the dash mounted control panel. Although the cables would be much longer, I think it may actually be easier to install into the car. I'm finding with the dash mounted control panel being so close to the HVAC box that the cables are too cramped. Especially with how the control levers don't necessarily aim the cables in the ideal directions for the AC version of the HVAC box. Not only is it difficult to get everything in there, but the cables have more curves, which creates more resistance when operating them.

But I also like your idea of a more "automated" system with a Arduino. Unfortunately I know nothing about them. Eliminating the cables all together certainly would make things easier to assemble (at least from the perspective of the cables). If you decide to do it please post all the details, I'd be interested to learn how it works.

By the way, speaking of "automating" the system. I think the way Fiat made the vacuum control unit, with its overly complex design, redundant wiring, push button operation, vacuum solenoids, etc, was an attempt to "automate" the climate control system a bit. Akin to today's electronic HVAC controls where all functions, cabin temperature, etc, are activated by touching a single button on the dash. Unfortunately it really failed in my opinion. Which is why I decided it was better to eliminate it rather than restore it.

Question for you. When you said you dislike AC in the X because the cabin is too cramped, what do you mean? As far as I see there is really nothing more in the cabin with AC than without it. A bit more going on behind the dash, but not in the cabin. The controls are the same size and location either way. The HVAC box is a little larger with AC, but that behind the dash....or is that what you mean by in the cabin?

 

[darwoodious]

Yeah, I mean the giant and more complex heater box, the pump, lines, evaporator etc. And just servicing the thing gets more complicated as has been discussed (even recently) here.

I haven't given up on it yet which is why I kept the early box. I'm sure the squirrel cage fan itself is twice as efficient as the lame/noisy 4 or 5 blade non AC fan and maybe I'll want AC later.

Cheers.

 

[carl]

I'm not really into this thread that much but my NA Miata with AC has what appears to be mechanical controls with three slide switches like a non AC X. Maybe this setup could be used on an X? The AC matrix is totally separate from the heater box with just an air tube connecting them but I don't think there is much room behind the dash on an X to locate the AC matrix of a Miata.

 

[Dr.Jeff]

I've been fooling around with various ideas to add some sort of filter to the HVAC box, in an effort to decrease the amount of debris that gets into it (and the passengers). While playing with the box I realized that the arrangement I had worked out for the "defrost" control cable won't work as I intended. On the bench it's fine, but in the car not so much.

As I noted previously the vacuum controls for the AC style box are located differently from the non-AC box. In order to maintain the correct assignment of the control levers (dash slider unit) to their respective functions (icons), one cable is pointing in the opposite direction as it leaves the control assembly (the back of the slider is facing the wrong side of the unit). Now to route the cable from the control unit to the defrost door, and clear everything around the dash and chassis, it will have to approach the 'defrost door' from the other side than planned. This means the slider is working "backward" - the movement of it will be opposite the other levers for "open" and closed". There are a couple workarounds that would keep the slider movement in the preferred direction, but they are rather involved and makes everything more complicated. So for now I'll continue with it moving in 'reverse' and see how I like it. I'm sure more ideas will pop up as I work on it more.

 

[Dr.Jeff]

I finally got back to doing more work on the HVAC box mods today. It was in another thread where I discussed using a VW blower resistor unit to control the blower speeds, but now I can't find that one. So I'll just add it here.

Basically I wanted to eliminate the stock blower motor speed control resistor unit....

I've found all of mine to have very high resistance values (which only causes the blower motor to turn even slower that it did when new), and in my opinion they are a fire hazard - especially being located in the vent scuttle where a lot of leaves and debris collects around them. That location also means the wires to it begin at the dash control switch, travel up the dash and all the way over to the extreme drivers corner of it, where they pass through the firewall, into the front vent scuttle, and over to the stock resistor unit mounted next to the wiper motor. These are four heavy wires and they are extremely long for such a high electrical load.

I wanted to replace it with a more modern design from VW. The newer ceramic type is much smaller, more reliable, and made to fit inside the HVAC box rather than in the front vent scuttle. This will preclude the fire hazard and allow MUCH shorter wires to run from the dash controls to the resistor unit. Plus it has the same resistance values as the original Fiat unit had when new.

Here is the VW resistor...

I trimmed the rectangular mounting end a little (arrow above) to allow it to fit in a narrower space. As for wiring the unit in place of the stock one, you can simply plug the original wires into the VW unit if desired. Here is a diagram of how the connections compare to stock...

In my case I also wanted to install relays to take the blower motor load off of the dash control switch and the rest of the stock electrical system. And as already mentioned, by mounting it in the HVAC box I could easily do that while shortening the wire harness.

The AC version of the blower is has 3-speeds and is controlled on the "negative" (ground) side of the circuit. The non-AC blower has 2-speeds and is controlled on the "positive" (hot) side of the circuit. However the same resistor unit can be used for either setup.

To mount the resistor in the HVAC box I cut a rectangular hole in a place where it would not interfere with anything inside, and would be on the "air inlet" side of the box....

I mounted the resistor with a couple of tiny screws...

For now I mounted the relays onto the side of the HVAC box right next to the resistor unit. Once I get the interior ready to go back into the car I will see if I want to keep them there or possibly mount them on the firewall in front of the box....

You can see how short the wires are with this setup. The original wires from the dash switch now only serve to trigger the relays. And the switch is very close to this location so even those wires will be short. Normally I use relay holders (connector base) to attach wires to a relay. And for the VW resistor unit there is a common electrical connector that fits it. But in this case I elected to not use the relay holders nor the resistor connector to save space in a already tight area. You can do it either way.

The red wire at the bottom of that last picture will connect to the blower motor connector ( just seen on the very right side of that pic). The black wires go to a convenient ground. I'll post a generic schematic for adding resistors to a blower motor at the bottom of this post.

That's all there is to it. The VW resistor was $5 (delivered) on eBay (look for part number 64111499121). For you Fiat purests, the exact same part is also installed on some newer Fiats. So if it makes you feel any better you can tell yourself it is a Fiat part going into your Fiat.

This diagram is for a negative controlled (AC version) system. It shows a four speed setup, so I crossed out one section of it for use on a three speed system. For a non-AC blower just swap positive and negative feeds at the relays. And for a 2-speed blower only use two of the connections rather than three on the resistor (i.e. two relays)...

 

[Dr.Jeff]

Something has occured to me about the wiring for the blower motor. As described, the AC version controls the motor's speed through the "negative" lead (ground side of the circuit). Therefore the load of the motor passes through the resistor unit and through the control switch on the dash before grounding the motor. That is why the relays are added, to remove that load off of the dash switch. However that does not address the motor's "positive" lead (power side of the circuit). The power lead comes off of the fuse box directly to the motor. Therefore I believe the same load (from the motor) is also placed on that side, as it is on the ground side? Since the fuse box is run through the ignition key switch on the dash, it seems adding relays on the negative side will not protect the key switch? As noted they do protect the dash switch that selects the blower speed, but am I correct the key switch is still loaded as before?

EDIT: Question answered, I think. See next post.

 

[Dr.Jeff]

I think I answered my question about the load from the motor (previous post, #15).

The positive lead to the motor comes from the "P" fuse (#14) on the fuse box. That is one of the fuses that's supplied directly from the brown wires off the battery. So it does not go through the ignition key switch like many other systems do. Furthermore there is a relay in the stock fuse box (for a AC equipped X) that triggers the power lead to the motor. Therefore there is no load on the key switch due to the blower motor (on a AC equipped X). [Note: It seemed odd to me that Fiat included a relay for this power lead when so many other circuits are not relayed. But without a relay the blower motor could be left running when the key switch (and engine) is off.]

Since the blower speed resistors are on the ground side, all of the added resistance (when slower blower speeds are selected) is put through the dash blower (speed selector) switch, and not the ignition key switch. Hince the benefit of adding relays to only the negative side of the motor.

Remember that on a non-AC equipped X it is the opposite, the blower motor is controlled by the positive side of the circuit.

 

[Dr.Jeff]

A little update on this project. As I finally began to reassemble the interior of this X it became apparent that the location of the relays I did previously (see post #14) wasn't ideal. Really nothing wrong with where they were but I saw that they would be better located at the rear of the box instead of on the side. Overall it makes the whole thing a bit more tidy and easier to connect everything. So I've relocated the relays and the resistor pack to the middle section of the housing at the back side (front of car). This also simplified the wiring connections once my custom harnesses were complete. Here is a pic of the new location: