the fan switch probelm is null. my car is a 94 with a new fan switch and I just installed my PFC and I get no AC in any setting. The commander says it's on but it's not. the wierd thing is the commander thinks it's on. in my last car whatever setting the AC would not work on the commander would not show it on. Now in this car the commander thinks its on all the time every setting but it's actuallt never on. stock ECU and all it well.

Zerobanger.
the reason your AC is blowing colder than ever. the stock ECU uses a thermoswitch input to cycle the compressor on and off. This keeps teh evaporator temperature in is's most efficent range. this way whe you are not using the A/C much say setting 1 the compressor will only be on 1/4 the time it'll be on in setting 4.
the logic to operate the A/C compressor is simple yet a bit complicated.

Ill have to do some testing to see why mine is not working at all.
im at the point where Ill be making a little simple ttl board to rin the logic just like the ECU to get it all working.

 

This is a great thread.

 

is this thermoswitch normally open or normally closed? i'm trying to integrate a/c control with my haltech....

also, is it simply closing/opening a circuit that is grounded to kick on the a/c relay, or is it running some sort of voltage?

the haltech wants an "a/c request" input with a voltage range from 0-5v, 0 being low mode, 5v being high mode

so confusing!

 

found out thermoswitch is normally closed

 

I find the solution logical to a point. The evidence is there because it works now. No problem there. I wonder is how much does the switch have to degrade before it fails again. I see how the PFC could be looking for a different reading altogether. I think and its just my nature to be careful, the problem is more complex and a buffer may need to be installed in-between. Each circuit in the fan control has an overall different resistance. The common thread is the activation of the compressor and speed 3 and 4 do generate a pulse to adjust the idle speed up. Something for me to think too long about once again.