a/c

Typically the compressor clutch is controlled by the high, low and thermostatic switch. I'm just thinking out loud here. Low pressure switch should keep the clutch from activating from low ambient temps or low charge. High pressure switch is a safety to prevent excessively high pressures. Thermostatic switch should open when the evap core cools to just above freezing. Now you say all 3 are new and the clutch disengages when you turn the A/C off. That should rule out a short to power in the clutch circuit. Without having the truck in front of me my guess would be that maybe there is an issue with the thermostatic switch in the core. Cuts and sharp bends can damage the probe and the switch won't work right.

 

A truck I drove 6 years ago had an a/c problem. After changing all the switches, the mechanic thought it might be in the loom, so he bypassed it, but forgot to wire in the tthermostat, so it iced over. He wired in the thermostat, then it worked well.

Maybe there is a broken wire for the thermostat?

 

It's a plugged evap. Just went over this in class today. If your evap can't collect heat by air going through it then the evap outlet (suction line) will freeze up.

 

I think it's the trinary switch on top of your air dryer. That's what controls the compressor turning on and off based on pressure.

 

Yeah the fins. It shouldn't be the heater core cause the plenum should have a blend door that blocks the air flow from it when you want a/c.