2004 Peterbilt 379, Ok so I am a bit confused on this, AC not working in truck, no power to compresoor, if I jump across the high and low pressure switch (which both have been replaced) I get power to the compressor, however I can not turn it off by the AC switch on dash it's just constantly on. I have power to the switch but as soon as I turn the switch on I have no power anywhere, including the power running into it. As far as I can tell no blown fuses just no power running out of the switch. But from my understanding of the wiring diagram I also should not have power running to the high and low pressure switches without power running out of the switch.
check for a melted "fusible link"...that is a wire, that is actually a fuse, in line and many times has a tag molded on it, specifying "fusible link"...sometimes they are purple in color, sometimes red. it could also be the a/c is low on refrigerant, and this is why it will not turn on. check for an oily hose, indicating a leak, check all fittings for oily wetness as well. given the age of the truck, and miles on it, i highly doubt its all in great shape.
Everything in the system was replaced 3 years ago, I am working on wiring, system shows it is full on refrigerant. I will check that again, that was my one thought also, but I still think it is going to be something in the wiring, I will check for any fusible links, thank you.
Unless they changed later models, the switch when turned on sends a ground to the thermostatic switch, to low pressure, to high pressure then to the relay, where it grounds the relay, which then sends power to the clutch. So, there would be no power through those switches, just grounds
Since I have power to the switches and no power running out of the dash switch, I am assuming the relay is bad or something to do with the relay. Will tear into it further after this week, thankfully the temp drops tomorrow and I can do with out for one more week, but today has been a hot sob in here.
