I’ll try to make this as short and sweet as possible.
Two weeks ago my a/c gradually moved from blowing cold to blowing warm over the course of three days. Initially I figured it was low on refrigerant so I bought a can, opened the hood, and the clutch on the compressor wasn’t engaged. I assumed the low pressure switch was functioning properly so the next step was to fill the system and search for a leak later. Upon removing my low port cap, after two turns, it blew off like a rocket!! Lots of pressure in the low side! I knew that wasn’t good but I wanted to make sure the compressor was “ok” so I jumped the clutch through the WOT relay at pins 87-31, and like magic, the clutch engaged and the a/c was blowing cold! I put gauges to the system with the system jumped and running and it was low on refrigerant. I knew I had that bad schrader valve but wanted to see if it would take refrigerant and hold it long enough to disengage the jump and run the compressor for even just a second. It didn’t!!! As soon as I got it full, replaced the low port cap(no check valve yet) and removed the jump wire, the clutch disengaged and the system was once again blowing warm.
My question is, what the heck is going on here!?
I failed to mention that I did replace the WOT relay.
Not all A/C systems are the same. What year Explorer?
It’s thate @$%&*ed R134.
You already know that you have a leaking schrader valve, I would suggest you replace that first before going on with other testing. It’s only a few $$.
I replaced the valve, refilled the system, and the issue persists. Cold air when I jump it but warm air once the wire comes out and relay put back in.
The year and sub model is 1997 XLT 5.0
I’m not really sure where to go next in the diagnosis process. It couldn’t be an expansion valve because it blows cold when jumped. It couldn’t be a blend door issue because it blows cold and through the correct vents. It couldn’t be low pressure switch, since I jumped from the WOT relay and didn’t bypass the low pressure switch, could it? I’ve spoken with several mechanics and nobody wants to deal with a diagnosis. They’re all quoting me $800+ for a new system. I don’t have $800 and if I did, a new system seems completely unnecessary at this point. Thanks!
Excuse me if I misunderstand, but have you swapped relays?
I swapped the WOT relay but that’s the only a/c related relay I could find in the book. I know there has to be another but I don’t know where to look. I’m not a mechanic by any definition. My only experience is in commercial and residential hvac which I no longer do.
There’s nothing wrong with compressor if the clutch engaged and it was blowing cold air out the vents.
Try swapping the WOT relay with another relay with the same part number. If the clutch engages, replace the WOT relay.
Tester
That was the first thing I swapped before I put in the new schrader.
Well then, you’re not going to like what I’m going to tell you.
The Power Train Control Module is what controls the WOT relay.
Tester
Ouch. So even though I jumped the compressor through the 87-31 pins of the WOT relay, it could still be the pcm?
Yes.
You just substituted the contacts in the relay that the PTCM isn’t closing with the jumper wire.
Tester
Honestly, it’s not that bad of news. It would cost me about $200 to do a new system job myself at home and a rebuilt pcm is about the same. I’ll mark this one up as a win. Thanks!
Check the cavity for pin 85 of the WOT relay for power, it should have power when the engine is running. The PCM controls the ground on pin 86 to switch the relay on.
Just in case check interior fuse 18 says heater-ac eatc module, no idea what it means, it was for an explorer, but maybe yours is the same.
Yes sir I replaced that fuse even though it looked fine. Should I use a multimeter or test-light for the 85 pin?
