Carb cooling fan wiring

[Luckyd77]

I've been trying to get my carb cooling fan operational before the summer gets here. I ran a wire from the broken off wire to the sensor and it didn't make the fan operational. I then grounded the wire and that didn't do the trick either. I was looking at the fan and noticed a place where there seems to be a wire missing. Am I wrong?

 

[CornbreadJR]

Mine looks similar and it doesn't work either. I have multiple connectors that lead no where. Post your results as I'd like to get mine working too.

James

 

[Slow Left]

Check the "Dome" fuse in the main fusebox in the vehicle cabin. The carb fan and the dome light are on the same fuse circuit.

 

[Luckyd77]

Will do! My dome light doesn't work either...

 

[Luckyd77]

It was the DOME fuse. I changed it and now when hooked to the sensor or grounded, the fan blows. Just in time for the summer. Thanks!!!

 

[Slow Left]

Are you worried about overheating?

How long have you had the vehicle?
Any idea how old the radiator, water pump, thermostat and hoses (including all the heater hoses) are?

High mileage and original parts...You might consider, if the funds allow it, to go ahead an replace the cooling system in a single shot, instead of nickle and diming it and blowing hoses every other month. It's what I ended up doing after getting tired of replacing each 30 year old heater hose after the other (after having installed a new radiator, water pump and thermostat). After you replace one, the weak link in the system becomes another 30 year old hose...and so on...

 

[Luckyd77]

I'm not overheating anymore. I replaced the thermostat, the worst of the hoses and did a coolant flush. I was however getting the typical hard restarts after going on extended drives.

 

[ModisetteJ]

Hey guys, any idea what to do if the carb cooling fan still isn't coming on after you've replaced the blown fuse?

 

[Slow Left]

Hey guys, any idea what to do if the carb cooling fan still isn't coming on after you've replaced the blown fuse?

There are several other components in the "Carb Cooling Fan" circuit that might be responsible for the fan not functioning.

You might consider first temporarily grounding the circuit to see if the fan comes on. For instructions on how to run this test, see post #4 in this thread:
https://forum.ih8mud.com/threads/carb-fan-is-it-working.801129/#post-9274583

When you run that test, what you essentially are doing is controlling the ground of the circuit. Normally the temperature sensor near the exhaust manifold is responsible for grounding the circuit. When the temperature at the sensor is hot enough (i.e. the exhaust manifold is hot enough, so the air around the temperature sensor is hot enough), the electrical resistance inside the sensor material changes and allows the circuit to 'see' ground (when the ignition switch is turned off, too). When the circuit grounds, current flows through the circuit and the fan will kick on. There is a timer on the circuit too (see post #11 in the link above...it shows the "Carb Fan Computer"...which I believe is just the 'timer', but I'd have to double check the FSM...) which will interrupt the flow of current after a certain amount of time with the ignition in the 'off' position, regardless of the state of the temperature sensor...

So, if you run and pass the test, then all your components are working, except the temperature sensor. If you don't pass the test, then the temperature sensor is or isn't functional, but in addition, another one of the components is not functional...I'd pull and check the "Cooling Fan Relay" (see post #11)...check FSM for field test of the relay...

 

[Output Shaft]

Hey guys, any idea what to do if the carb cooling fan still isn't coming on after you've replaced the blown fuse?

Follow Slow's instructions carefully...
Then, if your head explodes and it still doesn't work, just do this instead and be done with the headache. Spring wound mechanical timer. 12V is fine

 

[ModisetteJ]

There are several other components in the "Carb Cooling Fan" circuit that might be responsible for the fan not functioning.

You might consider first temporarily grounding the circuit to see if the fan comes on. For instructions on how to run this test, see post #4 in this thread:
https://forum.ih8mud.com/threads/carb-fan-is-it-working.801129/#post-9274583

When you run that test, what you essentially are doing is controlling the ground of the circuit. Normally the temperature sensor near the exhaust manifold is responsible for grounding the circuit. When the temperature at the sensor is hot enough (i.e. the exhaust manifold is hot enough, so the air around the temperature sensor is hot enough), the electrical resistance inside the sensor material changes and allows the circuit to 'see' ground (when the ignition switch is turned off, too). When the circuit grounds, current flows through the circuit and the fan will kick on. There is a timer on the circuit too (see post #11 in the link above...it shows the "Carb Fan Computer"...which I believe is just the 'timer', but I'd have to double check the FSM...) which will interrupt the flow of current after a certain amount of time with the ignition in the 'off' position, regardless of the state of the temperature sensor...

So, if you run and pass the test, then all your components are working, except the temperature sensor. If you don't pass the test, then the temperature sensor is or isn't functional, but in addition, another one of the components is not functional...I'd pull and check the "Cooling Fan Relay" (see post #11)...check FSM for field test of the relay...

You're the man. Thank you so much.

Follow Slow's instructions carefully...
Then, if your head explodes and it still doesn't work, just do this instead and be done with the headache. Spring wound mechanical timer. 12V is fine

View attachment 1048912

View attachment 1048913

I might end up doing that at some point! Right now it's just grounded and running off its own timer (~20 minutes)

 

[Cruzerman]

Don't get the timer thing. As its been noted, the unit already has a built in timer.

 

[Output Shaft]

and it works great... if it works.

 

[ModisetteJ]

I just grounded the wire and it runs for about 20 minutes then shuts off. This won't drain my battery will it? I use my cruiser as a DD.

 

[Output Shaft]

The carb cooling fan draws 2 amps when running (per hour).
In 20 minutes it'll pull 666 mA from the battery before it shuts down..... Almost nothing.

 

[DFXR]

Mine has been grounded to the body with an alligator clip for almost 3 years. Runs for 20 every time I shut it off. No issues with the battery at all. And the working fan has a definite positive effect on hot starts.

 

[Output Shaft]

When my carb fan used to work properly with the thermosensor on the manifold bracket, on hot days (engine hot but not overheated) the fan would sometimes run for 45 mins. On cool days it would run less.

 

[Output Shaft]

The carb fan also serves an additional function besides improving hot starts. The cool air blowing into the engine compartment cools down the carb, manifold & engine compartment after engine shutdown which slows down the evaporation of the fuel in the float bowl of the carb.

As anyone with a 2F has noticed, if the engine is not run for several days, the fuel in the float bowl disappears and subsequent start up takes a few tries to fill the bowl. So where does the fuel go? It evaporates and the vapors drain out of that big pipe near the top of the carb which end up in the charcoal canister.

A large percentage of the fuel evaporation out of the bowl occurs during the first few hours after the engine has shut down, when everything is as hot as the sun. The quicker you can get the carb, manifold and engine cooled down, the slower the fuel will evaporate out of the bowl... and maybe (if you're lucky) you'll be able to start the car on the first try four days later.

 

[ColtCruiser13]

Hey guys, any idea what to do if the carb cooling fan still isn't coming on after you've replaced the blown fuse?

Try grounding the wire that goes to the senor out it should turn on if not you have a power supply problem, if it's not the fuse perhaps the power got cut or is shorted out somewhere.

 

[chuckost]

Since we're on the subject of cooling fans! 78fj40. Sorta got the controller to work. Previously nothing. Resoldered all joints on the pic board. Then, yay! Sorta... Turn off key, it comes on always, hot or not. And never shuts off! Gonna keep tinkering until I get this working. It's just a matter of pride now! Next step, take to electronics shop not too far and see if I can get them to figure it out.