I have a 1991 Z28 with the dual electric fans. The fan wiring has not been altered. My passenger fan will turn on as soon as my key is in the on position (just like diagnostic mode) and will NEVER turn off. This is making my car run colder than desired, in the 130-140 range. At one time my car did not do this, but I noticed it after I got my AC recharged and a custom PROM. I just can't figure out what could cause the passenger fan to continually run.

 

Bad temp switch (shorted to ground)??

 

I initially thought it was a bad prom, but I put another one in and it still does it. I find it strange that it started around the time I put a new prom in and got the AC serviced.

 

there is a switch in the aircon system, maby that is faulty?

 

That is a possibility. When I got the AC serviced there was a bad switch up near the firewall on top of that bundle of wires. We just jumped it with a wire until I got a new switch, but maybe the new one isn't correct and makes it stay on? I'm going to go disconnect that switch and see what happens.

 

if that switch was just wired up (allwase on) it will make the second fan run nonstop because that is what turnes the fan on when the aircon is on.

EDIT: I THINK!

 

I just went and unplugged the switch from the AC and it still runs as long as the key is in "On". Man this is annoying, I wish I noticed the EXACT moment this started happening. I just know it happened sometime after I got my AC serviced.

 

I just did a search and found a wiring diagram hope it helps

https://www.thirdgen.org/forums/atta...ng-fans-wiring

 

At this point maybe I should trace the fan wiring system. It is just strange that one week it was fine, then next week I noticed the fan was always on. I've ruled out the PROM change as a cause by swapping PROMs. I thought then it MUST be AC related, but I just unplugged that switch and it still runs. I'm stumped. No alterations to fan wiring have been done since the fan was ok.

 

1 FAN RUNNING
My 91 Z also started to have the 1 fan run all the time.
Its hot in Texas so I didn't notice exactly when it started. I have changed the a/c to R134, some sensors, the engine has been in and out several times and the chip re-burned. I had a lot to go over and check. I have checked just about everything. I am still not 100% sure but, I think I might have a ground issue as I have measured a micro voltage at the relay trigger. This could still be a bad sensor. My current thinking is that there must just be enough voltage to get the relay to latch.
I have not had a chance but, I am thinking of trying a resistor on the relay trigger to see if I can get it to stop latching with anything less than a full 12 volts.
RUNNING COLD
As for your car running cold I think you may have another problem like a stuck thermostat or inaccurate sender/gauge. I recently moved to Canada. I still run a 160f thermostat and have never had the car unable to warm to at least 160f in sub zero weather with my 1 fan running all the time. I didn't trust my gauge so I had it checked. As it turns out my gauge is reasonably accurate.
Keep us posted I'd love to know how you finally get the fan to stop running.

 

There is a gray wire in the harness that runs to the relay for that fan and for some reason it is always grounded which results in the fan always running. So if I want to fix the problem then I'd have to pull the harness and trace the problem in that wire, so the hell with that. I just installed a new Be-Cool 180* thermostat and it must have been bad out of the box. I agree that the fan alone will not cause it to run so cold, and with the fan unplugged it barely gets to 160 just sitting at idle. I'm going to swap in a new 180* thermostat and make the pass fan run off the driver fan trigger.

 

Pull the wire off the temp sensor on the passenger side of the engine. I'll bet the fan stops. If it does, that sensor shorted to ground.

Don't wire it into the other fan. They're separated for a reason: If one system fails, the other one will keep your car from overheating.

Drain about half the radiator before you remove that temp sensor to replace it, or it will all land on you! (don't ask)

Rayvan

 

I had the exact same problem, my secondary fan ran constantly. Turns out it was my fan temp swtich between the 6 & 8 plugs. The connector fell apart in my hands, it was the original. I replaced the connector & fan temp switch and it stopped running all the time.

 

That isn't the cause. I just replaced that but in the process of locating the error I disconnected it to verify it was wired in correctly. It is the gray wire running from that fan's relay into the harness. It is corroded, torn, or damaged somewhere within the harness and is grounded constantly.