Hello all,

The aux cooling fan on my 81 is not working. Can anyone shed some light on how I can diagnose what the cause is? I don't want to throw parts at it in hopes of fixing it. I want to diagnose the cause and replace as needed. The car is an 81 and is all stock except for the radio.

TIA, IronIvan.

 

how do you know it is not working? i think it is set to come on only above ~235f..
you can ground the temperature switch and see if it comes on..

also see

Wiring expertise 79l82 auxiliary fan control with ac and bypass option - CorvetteForum - Chevrolet Corvette Forum Discussion

 

I believe you can jump the blue and black wires at the switch on the rear of the driver's side head. The blue wire should have 12 volts, while the black completes the circuit to the fan motor.

 

yes and nope ..if 2 wire they complete the ground.. no power at temp switch..at least a 79, also 79 passenger side

 

I stand corrected. The fan is powered by a 30 amp breaker in the fuse box, which supplies power to the fan. The switch grounds the circuit at 238F, But the switch fir 81's is on the right side rear head..

 

Hello all, thanks for the suggestions.

I am not 100% sure that the fan isn't working. I have run the car in park and have watched the temp gauge go from 210-230. I know that the temp gauge may be inaccurate. Since I live in AZ I am concerned about the summer heat.

I will check the fuse and try grounding the switch this weekend, and let you know what I find.

Another question: Does the AC have to be ON in order for the fan to run, or is it only triggered by the switch on the right rear head?

II

 

This information is correctThe fan is powered by a 30 amp breaker in the fuse box, which supplies power to the fan. The switch grounds the circuit at 238F, But the switch for 81's is on the right side rear head..

You can test the fan as suggested by grounding the wires together at the sensor. There is also a disconnect plug that runs along the passenger side front fender. You can test it by powering up through the plug and while you are there check for resistance. With the temp switch set at 238 it is almost useless anyway, you are running too hot already, unless you want to tie it into the AC low pressure switch with a solenoid to turn on every time your AC clutch turns on. But you will also see little benefit, I have tried those options, but the best was to buy a DeWitts radiator for the 81 and replace the existing thermostat with a 180 degree, OEM standard. My 81 always runs cool with those installs and never see it above 195 on the hottest days in Florida. The fan never has a chance to come on at 238 degrees.

Good Luck

 

this is correct..
OP- read the thread i just did with fan and aux AC running..and where to tap without cutting anything..any increased air flow will help lower pressures in the condenser
also i went 180f thermostat, and have dewitt's radiator..and i live in Indiana

 

No A/c does not have to be on.

 

The full circuit is battery positive to the ignition switch, switch in run to the fuse, fuse to the fan, fan to the normally open temperature switch passenger side head near the dipstick, temp switch to ground. So, two things need to happen for the fan to run. Ignition has to be in run and the temperature switch has to close which it will do at 235. To check the fan, I'd start like another said, pull the two wires off the temperature switch and clip them together. Then put the ignition switch in run position. If the fan starts, then it's fine and the only possible problem is the temperature switch. But unless you see your engine temp exceeding 235, then I would not expect the aux fan to come on. If it doesn't start with the ignition in run and the temp switch wires clipped together then possibilities are:

• blown fuse - easy to check
• bad ground on the temp switch ground wire - get a meter and check the ground from the ground wire lead on the switch to a clean spot on the frame
• bad fan motor - leave until ruling everything else out or simply find a good 12 volt positive source nearby, put it on the positive side of the fan and ground the lead that goes from the fan to the switch
• bad connections - either of the contacts in the connector to the temperature switch or a couple others along the circuit
• broken wires

But my guess is it either works fine and just never tripped the temperature switch, a bad motor, or damage on the connector to the temp switch - mine melted and fell off when I had headers on the car.

Now, how rare is it to exceed 235? I've owned a 1980 L82 since 1980. I bought it in south Texas and being 21 years old I gave it a hard youth. I lived in TX for almost 3 years. Then I did a stint in FL one summer. Since then it's been in the NY and PA. In all those years and 90k miles the aux fan came on only once. That was after about 10 miles of hard pedal to the fiberglass binary running - binary being either full throttle or off throttle and hard braking. After that I shut it off behind a barn. But when I shut off the car the interior light came on, and as this was at night it made the car visible from some angles on the road. So I put the car in run without starting it to get the light off. Why it was important to not be seen from the road and what led to the hard driving in the first place has been told in one or more of my past posts so I won't bother with it here.

A minute or two after shutdown, I heard a strange sound. It was the aux fan coming on. Apparently, the heat build up in the engine kept raising the water temp until the temperature switch closed. That is what it took to get that fan to come on in my experience. Typically with a 180 deg thermostat I never see over 190 on the temp gage.