I'll try and make this short, 04 s40 AC started blowing warm air. I noticed cooling fan was not turning on when ac was switched on.
Ok, so now i figure system is getting hot and one of the ac pressure switch is killing the ac. So now im looking at the fan, I also noticed
that the fan wasn't switching on at all, but the car never overheated. temp gauge is working properly. I jumped fan it started right up, so now im thinking
its the fan module, nope that's not it. So does the high pressure switch control the fan? and the low pressure switch kill the ac when there is too much
pressure built up? If it's not one of the pressure switches what else could it be? I have checked all fuses, is there a relay somewhere not in the fuze box?

 

The fan will be controlled by the pressure switch the same way the A/C compressor clutch is. My guess is that you simply have too-low pressure in your system, so the pressure switch is keeping both from starting.

 

AC is working properly, fan does not turn on, ac gets hot builds pressure and shuts off.

 

It would be interesting to verify that if you jump the fan and have it running, will the A/C continue to operate normally (I'm guessing it will).

I don't have access to any wiring diagrams for your car, but it sounds like you're going to be chasing the "turn on signal" from the A/C system to the fan controller (relay?).

Hopefully someone who has the info can chime in here...