06 M1165 AC Issue

[Nethawk86]

Just picked her up. Owner said he never messed with the AC but when he connected the 3 wires under the passenger side dash and turned the key, it started smoking, so he unplugged it. Vehicle is in very nice condition, and besides a very hard shifting transmission from 1st to 2nd (will figure that out next after fluid changes), its killer! I took off the dash vent shroud cover to repair all the heat cracks in the plastic (since everyone wants $700+ for it) and figured id try and see myself what he was talking about. The 3 wires only connect 1 way, so there wasn't any chance he connected something wrong (which he did with the tail lights when he upgraded to LEDs). Factory AC, 6.5 Turbo Diesel, 4L80E.

Plugged them together, turned the truck over into RUN, not starting the engine. Then flipped the fan switch to High and I could hear the fan pulsing a few times before smoke came out followed by a "PFFFFT" sound. Smoke was definitely electrical in smell. Immediately turned off and let it sit for a few minutes. Checked over everything and nothing seemed burned on the outside (but will check thermal next). Unplugged the wires, turned the vehicle back over to RUN again and flipped the fan switch to HIGH and then LOW. Both working fine now, not pulsing or anything. So fan/blower motor works fine when not connected. And the smoke/sound came from the unit under the passenger dash where the blower motor is.

 

[DREDnot]

How was your rear AC evaporator/blower box acting during all this?
What were the numbers on the metal tags on the wires you were unplugging?

 

[Nethawk86]

Honestly, I didnt even look/hear/feel what the back box was doing. I was focused on making sure the front didnt catch fire....darn. Tags are 435 and 438

 

[DREDnot]

Those go into a small black box on the side of the evaporator assembly, correct?

That is the "temperature switch" that senses if the evaporator core ices up and shuts off the compressor till it thaws out. The two skinny white wires are for the temperature probe.

When the wires are unplugged the fans (front and rear) run, but the air that comes out is not cold because your compressor is not engaging, correct?









If you plug the two wires 438A and 435D together it effectively bypasses the switch and your compressor should kick on and make cold air.