i have a 1991 TBI 305, when im running my A/C, my temperature gauge remains cooler, for instance, when im in a drive through...but if i turn off the A/C, then the engine slowly starts to overheat.

also note, my electric fan no longer kicks on at 220 degrees anymore. the fan switch was the problem in the past, but it keeps getting burned up or something, so its just a waste of money trying to fix it (been done twice) ......

basically, the A/C is my new 'electric fan', because its cooling my engine, but why?

 

Isnt the secondary fan supposed to kick in while the ac is on...

That would explain the drop in engine temps.

 

when you turn on your a/c the fan turns on anyways, so turning on your a/c might cool the engine more than if there was no a/c on because there would also be no fan on.

BUT.....generally with a/c on it should eventually overheat if you have a mediocre or average radiator or fan....whilst going up hills with a/c on at higher alts, or sitting in the heat with the car running and a/c on

if i were you id get the fans working, bypass the relay and make your own switch and set the degrees to what you want it to, this is what i had to do for mine cuz fans weren't turning on at all

or wire them to be on all the time

 

There are 3 ways to test circuit falure in the cooling fan, and youve narrowed it down to the fan switch. Your options are run the wire that goes to the fan switch directly to a ground (fan runs when ignition is on), run a toggle switch, or get an aftermarket switch such as a hypertech 165 degree switch. They run about 40.00 but have a better warranty. I just grounded mine until I can get a better setup.

 

oh duuur, ya, guess your right, when the A/C is running the electric fan kicks on too...you guys are brilliant, or im just a retard that was never paying attention

 

Nah youre good, I had to read it before it sank in too.