I've got a 2002 MCS which had a problem with the low-speed fan not turning on with the a/c or with temp. Instead, only the high speed fan will come on for brief moments when the engine temp gets high. I replaced the fan assembly, and can now get the fan to run at low and high speeds by jumping the relays. However, the low speed fan still will not come on in normal operation when the temp rises or the a/c button is pushed. I'm pretty sure the electrical system from the relays to the fan is operating correctly.

Is there something on the control side of the relay that could cause this problem? Since it is failing with two separate inputs (engine temp and a/c), I'm wondering if there is a common ground that might be bad.

 

There is a resistor that fails on our cars that results in the low speed not working as needed. Unfortunately on the early cars the resistor is located on the fan housing, and can only be replaced by removing the assembly. Detroittuned has a replacement or the whole assembly is reasonably priced. If you just changed the fan, then you'd need to dig into it again. I assume your fan assembly has two electrical connections on the right side of the assembly as view from in front of the car which would indicate that you have the early setup. On later cars the resistor can be replaced by a new one you can locate elsewhere in the engine bay.

 

Sorry, I should have explained that I changed out the whole fan assembly, including the resistor. Now the low speed fan is working, but it looks like it mighty be iffy because the a/c compressor appears to be failing and can't keep the pressure above the set point for the fan to kick on. In fact the compressor just died on a second test drive and won't hold pressure, so seeing as it is original to the car I guess I'll swap in a new compressor and see if that fixes both the a/c and low speed fan mystery.

 

Please post your progress on the AC issue because I recently had low Freon and no cooling. It was topped up, no leaks found with dye, but if it fails again I may be looking at repair parts. Thanks.