I recently purchase a 1992 740 wagon. The air doesnt work . Took it for free Ac check they said your not getting power to the compressor . Wanted to replace compressor for 800 and not sure that is the issue . Is there anything simple it could be it's my understanding the 740 has no compressor relay if it does i can't find it . Any suggestions for diagnosing if the low pressure switch is bad or is the control banner i did read they go up on t his module any help appreciated

 

Did they check the pressures in the system. Go to the receiver/dryer and unplug the low pressure switch. Put a jumper wire in it and see if the compressor turns on. If yes then either low pressure switch is bad or you are low/out of freon.

 

Why replace a compressor, it's not getting power! A '92 740 is a 940, keep that in mind, unfortunately it is still with R12 refrigerant unless retrofitted later, does it have a sticker to that effect?

So first turn the car on and bypass the A/C pressure switch by the receiver/drier to see if the compressor kicks in. (Two pronged switch, just connect the two female parts with a short wire.) If it does engage, the pressure switch is bad OR you have no R12 in the system and it needs a charge. R12 is very costly these days if at all available. But at least you'll know if the compressor is OK. Best case you have a bad pressure switch and the system is charged. If the system is empty you have a leak which needs to be found and repaired before charging the system. You may be better off going to an A/C shop if the pressure switch is not the issue, and they won't be gentle with you. They will surely recommend a R132 retrofit and that plus whatever else...