2001 Peterbilt 379 ac help please

Long story short when I bought the truck the ac wasn’t working. Last August I finally repaired it and replaced the cab evaporator, condenser, compressor, office tube, dryer. That wound up being short lived and the Freon leaked out and the compressor burned up.

I just replaced the compressor, dryer, the schraeder valves (which is where it leaked), all 3 sensors. Because I didn’t want something small to hold out the ac. So I took apart all the lines, flushed each line and component with an ac flush kit. Pulled a vacuum for about two hours. Charged it up, and the compressor will not turn on, I charged it to about 110psi on high and low. The fuse box has a fuse for the ac which is fine, and a relay (don’t know how to test it) (but it should click when I turn the ac button on I assume, which it does nothing) I did swap the relay with one that I know works and it still wouldn’t work.

I have a couple questionable things that I noticed. The plug from the truck to the ac compressor was cut off and butt connected to the ac compressor from previous owner. When I connected the new compressor I did this same method, the ac compressor had a red and black, and from the truck is a white and black. I connected the two blacks and the white to the red. Which I assume would be correct.
The second item of concern, was after throwing in the towel and disconnecting my gauges. When I purged out the lines for the gauges, it had some of the citrus cleaner in it. Which means the vacuum didn’t probably pull out all of the flush chemicals. Does this matter?

My goal at this point is to get it to where it will run by troubleshooting the electrical problem that’s going on, then take it to a shop, have them evacuate the system, flush if necessary, and pull a good vacuum and recharge. Any help is greatly appreciated.

 

The sleeper lines were disconnected and capped off by the previous owner. So I haven’t bothered with adding that system back on.

 

First thing to try is switch the wiring around on the compressor, on the truck side white is ground and black is power, on the compressor red is power and black is ground. many compressors have a diode built in to help with spikes as it kicks in and out and because of this it will only lock the clutch in if hooked up correctly.

 

ill give that a shot. Thank you.

 

well I swapped the wires and still no go.

As a side note I learned how to test relays, all the relays measured about 76 when measured across the two posts 87 and 86 I think it was. Is it possible to have a bad relay even if the energizing section measures normal?

 

It's sometimes possible because of bad contacts inside the relay but rare. Can always swap it with one of the other relays for a quick test.

With key on and A/C set so that it should be on as well what do the pins the relay goes into on the fuse panel show?
For 85 and 86 one should show power and the other ground.
Same goes for 30 and 87 one should show power and the other ground.

 

Make sure the terminals aren't spread apart on the plugs for your pressure switches. Very common on older Paccar products.

You can use a safety pin to tighten them up if they are.

Check your thermostatic switch also. On KWs they supplied the ground for the relay, I would think it would be the same on a Pete.

 

did you flush the system when you put all those parts in? If you didn't, that's why you toasted the compressor. It will also plug up the sensors.

 

Yeah, it matters. A LOT!
Just re-read the OP. Did you blow out the lines, condenser, evaporator with compressed air after you ran that flush through it?
Did you add PAG oil?
Did you mix up the switches when you replaced them? Low pressure switch is N/O, High pressure is N/C.

I hate to say it but, it might be cheaper in the long run to let a shop fix your A/C.

 

Part of an additional problem I have is that the fuse panel cover was not there when I bought the truck. The one I’ve been using for reference is from the internet and seems to be 99% accurate. When I click the ac button there’s a relay below the ac compressor relay that isn’t referenced on the internet schematic that I can physically feel click. The one that’s supposed to be the compressor relay does not click with the ac button. At any rate I pulled the one that’s supposed to be the compressor relay and using a multi meter with the black lead put to ground, I wasn’t able to receive any reading on any of the fuse panel pins.