Replaced ac compressor, charged ac, no power to compressor

[troywalker83]

I've got a 07 town and country giving me ac problems... it came to my shop with a noisy compressor. Driver said it had been making noise for a while and finally got so hot it almost caught fire..... replaced compressor, filled with oil and freon. Still no power to compressor. Relay and fuse good. Pulled relay and have power in 2 terminals.. jumped power to compressor and turns on and blows cold.... could it be a bad pressure switch? Scanned ac system with scanner, no codes. Looking at the wiring diagram I have, not sure if the other terminal at relay should have power... I've got 2 with power and 1 going to compressor. 4 total.

[GM Tech]

The ECM throws a negative to the relay coil to engage the relay and thus the compressor....so your issue is upstream- as in an ECM input- no codes get set when this happens, either the low temp thermistor is bad, or the high side pressure transducer is amiss- look for 3 wires at the transducer- one is ground, one is probably 5 volts and the other is return or reference..

[troywalker83]

I've got the 5v reference. Ground. The signal voltage is 1.86. Says it should be between .451-4.519

[Jag987]

I replaced a compressor on a caravan once that had be removed and a bypass put in a couple of years before. Same thing, it would not come on. Fuse/relay were good, wiring all liked good, just no power to the compressor. I would have to look it up again, but there is a way to run the control head through a self diagnostic check. I did this two or three times then it started working properly. Might be worth a try.