Hi, My cars dual electric fans are not working like they used to. I just had a shop rebuild the motor. It is a 305 TPI. When they rebuilt the engine, 200 miles ago, they replaced the coolant temp sensor and also the cooling fan switch. I don't know which of the dual fans on my 91TPI is the main fan, and which is the auxiliary. I know that before the rebuild if I had my AC on or my defroster on. One of the cooling fans would come on early, at about 160 to 170 degrees. If I had the heater on or everything off, the main fan would come on at about 230 degrees. Right now only the smaller fan on the driver side comes on regardless of whether I am running the AC or not. It comes on only at about 230 degrees. The fan on the drivers side never comes on, regardless of whether or not I have the AC on or what the engine temperature is. The car never over heats, but behaves as if my AC is never on. Also, my AC compressor does not seem to cycle as it should. With the AC on it comes on for like a second every couple of seconds. Needless to say the AC no longer blows cold. Could anyone explain to me which fan is supposed to come when, and what my problems might be. I have an appointment to take my car back to the shop after the first 500 miles. I plan on asking them to address the issue then. In the mean time, they told me to keep an eye on the temp gauge and make sure that the temp doesn't spike above the 230 degrees. Any help in understanding how the electric fans on my car work would be greatly appreciated. I know that I did not have this problem prior to the engine rebuild. In fact other than this cooling fan issue and lack of AC, my car is running beautifully. Thanks a lot in advance.

The primary fan is controlled by the ECM and comes on around 220 degrees. The auxilary fan comes on when the engine temp reaches 238 degrees OR when A/C line pressure goes above a certain PSI(can't remember exact number) The auxilary fan is completely independent of the ECM. It sounds like the shop that did the engine work lost the freon charge on your A/C.

Thanks a lot for your reply. Would a loss in freon cause the AC compressor to stop cycling as well?
Also, do you know how difficult it is to re-charge my AC system? I think that autozone sells the freon and a recharge nozzle for it, but I have never done this.
Thanks again for your help.

Yes, when the charge is low but not enough to open the cycling/low charge safety switch continuously the compressor will cycle on and off rapidly. Eventually it will get low enough that compressor won't come on at all.

I've never done A/C work but the original charge on 3rd-gen F-bodies is R12 which the tree huggers got the EPA to outlaw sales to the public. An A/C tech with and EPA license can still get it but its pricey. If your car has been converted to R134A then you could try throwing in a bottle and see if that helps. It would be best to have an A/C tech do it to make sure the right amount and pressures are correct.

Thanks a lot for your help. I think my car has already been converted to the r134.