Carb thermo switch / relay

C

Caper X1/9

'78 Original owner
While hooking up the carb cooling fan to the thermo switch I was surprised when the fan kicked in (cold engine, '78 1300). Checked for continuity and the switch is closed, do I need a new switch, is it repairable? Changed out the thermo switch relay with the horn relay, both worked on the horn but the original horn relay when used with the carb thermo switch, the fan did not turn on. Which is at fault, switch or relay and let's not forget the obvious, me.
 
I had identical problem

Hey
that happened to me 3 days ago. The fan wouldnt stop even with ignition turned off. I disconnected the red wire that goes to the fan to quick fix it and then went hunting the cause. What I did notice is that the relay was real hot even though i had disconnected the red wire.. meaning the carb switch was closed allowing the relay to energise ( it is in the spare wheel compartment)
I wiggled the wires to the carby switch and the fan turned off... ergo the switch is shagged.It can be nothing else
15 bucks from midwest bayless.. dont buy the last one as I need one too!!!
 
Your switch might be okay

The circuit is designed to come on or stay on until the carb is cooled. Mighty surprised the first time that I was walking away from the car with the keys in my hand and the fan started up; a short time later it stopped.

David
 
Was the key on or off when it kicked in? The way I understand, it should only come on with the key off to prevent fuel from boiling in the carb when parked. I've never had one work right, so they always came out and went in a box....
 
Mine wouldnt turn off at all

Till I jiggled the contacts on the switch.. I think it is Furked so for 15 bucks I will swap it out
Nick
 
After the car has been sitting

for a few hours does the fan kick in? What happens when the engine is cold and you jiggle the contacts on the switch, does it come on?

David
 
Yes

I disconnected the fan the day before.. went back the next morning and remounted the relay and noted it was quite hot, drawing the conclusion that the relay was still energised even though I had disconnected the red fan wire. Once I reconnected the fan wire (engine not run for 12 hours) it went again so it was not turning off at all.. Thats when I jiggled the switch wires and got it to turn off.. i just left one of the carby switch wires off for now
 
Relay ground circuit

The relay on the F.I. version gets power all the time, the switching is on the ground side. The ground goes through the thermo switch and then the oil pressure switch, both have to be closed for it to come on. This is why it only works when the key is off. If the oil pressure warning light switch is working (goes out after startup) then suspect the fan thermo switch.
 
I dont think my oil pressure switch works

I havent noticed my oil pressure light on come to think of it..
The way i noticed the problem is during revving the car to see if i had bled the cooling system (the thermo fans were not coming on since i had done the cooloing system) I noticed a frenzied clicking coming from the spare wheel well and put my finger on top of the relay and is was turning of and on as if some posessed morse code was being transmitted.
If my oil pressure switch doesnt work, then it stands to reason that it may play a part but why then did jigglem the carby switch relay turn it off?
 
Now both relays are acting the same

I believe the one that was used for the fan needed some exercise. Removed the thermo switch attached the wire and clipped a ground to the threads. Now the fan does not come on, however if I momentarily bypass the switch (screwdriver between case and wire) the fan will continue to stay on until I remove the ground clips. Sounds like we are in the same boat. :sigh:

David
 
Fan would start with engine running

Hello Greg, in the past if I was sitting in traffic for any length of time with the engine running, the carb cooling fan would startup.

David
 
I found this while digging around in the various manuals I have on hand...
carbcoolingtroubleshoot.jpg


I couldn't find anything showing or saying that the CARB cooling fan is routed through the oil pressure switch, but that would make sense. I know that the FI cooling fan is routed that way, though. Run through these quick steps to troubleshoot that thing and let us know what you find.

EDIT-- I noticed that there was nothing about what to do if it runs all the time. I had to consult a different manual to find that info. I don't have it in digital format, so here it is - verbatim...

CARBURETOR COOLING FAN RUNS ALL THE TIME
NOTE
The carburetor cooling fan will run after the engine is shut off, even with the ingition key removed. This is normal.
1a. Disconnect gray/red wire from thermostatic switch. If fan stops, replace switch.
b. If the fan still runs, go to carburetor cooling fan relay.
c. Disconnect gray/red wire from terminal 85 of relay. If fan still runs, replace relay.
d. If fan stops, repair gray/red wire from relay to switch.

Interesting that there's a "1" and not a "2" in there...
 
The ground goes through the thermo switch and then the oil pressure switch, both have to be closed for it to come on.
Click to expand...
This is true for the fuel injector cooling fan, but AFAIK not the carb cooling fan. The wiring diagrams I have seen show the carb fan relay being controlled by the thermo switch only.
 
No worries Greg

Just think how much further ahead I am when I get a FI X. All knowledge is good. I think I see a new switch in my future. David
 
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