After I installed a power FC into my FD, I noticed that the AC compressor only seems to work reliably when the fan speed is set to positions 1 or 2. The compressor sometimes engages on fan speed 3 but not at all on speed position 4. The AC compressor seems to work normally on all fan speed settings when I have the stock ECM or a Pettit remapped ECM installed. So I’m guessing that my car is affected by the Power FC grounding issue that is documented in some other posts.

I would like to continue using the Power FC, but also need the AC to work on all fan speeds so I am wondering what the best fix is. I have read a couple different posts, one suggests using diodes and the other uses a relay to provide a better ground path. I hate to make modifications if they can be avoided, I am wondering if anybody has figured out why this problem is actually occurring in the first place so that a fix could be made without cutting wires? If the issue is marginal grounds, then which one? I know the grounds from the main engine harness are in good condition, and everything else in the AC circuit seems to work correctly.

I’d appreciate any feedback on what direction to go with this to resolve the problem.

 

Search power fc ac fix. Its usually an issue with the computer not seeing the ground from the climate control panel. Some cars do it, some don't. Basically you wire in a relay to boost the signal so the ecu sees it and kicks on the compressor.

 

Thanks, I saw that post and I guess I will implement that patch. It would be great to get to the root of the problem but maybe that would be more trouble than its worth.