What is the voltage in and out of the resistor?

Must be the hvac control unit, good news they are eaay and cheap to replace.

 

Ok the saga continues. I swapped the ATC unit from an 04 that worked, still didn't fix mine. The issue I am seeing is the output voltage from the ATC to the resistor isn't correct. I don't recall exact numbers but I measured the values off the 04 and as expected that changed with each press of the fan speed button. I think they ranged from 2.3V on low to 11 on max. Mine seem to stay around .5v until I reach max at which point it jumps to 10ish. I've now tried 3 different ATC's, 3 different resistor combos, new relay for both the power and resistor. What else could cause the ATC not to send the correct voltage to the resistor pack? I measured the Voltage at the connector coming out of the ATC. According to the RAVE the ATC receives input from the SLABS unit. I tried to measure that voltage but it jumps all over the place on both my slabs and the 04 donner truck I've been comparing against.

 

I dont really know, other than from chasing my own electric gremlins, but check the fuse box. See if it has corrosion or other damage. If it is the SLABS, you could probably get it repaired. Not sure where you are, but If you wanted to ship it to NJ, I gotta guy.

 

Sounds like it could be a wiring mistake, could have been modified? Maybe double check the wiring and compare to the diagram in the ETM.

 

All the wiring is correct, nothing appears to be modified. Everything checks out except the output voltage from the ATC to the Resistor pack.

 

Well after hours of tracing wires, troubleshooting, brain scratching... I swapped the resistor pack out of the 04 and plugged it into my truck and it worked fine. The 04 doesn't fit as it's a different style. Thankfully AB is going to send a replacement! So somehow I've managed to get two resistor packs that were defective!

 

Glad you got to the bottom of it.

 

Well the plot thickens. I got another resistor pack from AB and it did not solve the issue. Found a local 2000 parts truck to try one of my resistors in and it functioned properly. I pulled the ATC from that truck and installed it in my early vin 03 along with the resistor and it still doesn't work. If you install my resistor in an 04 it doesn't work. If I plug the later vin 03/04 resistor into my harness it works but doesn't fit in the blower housing. Seems my only resolution is to swap out the blower housing from a later model Discovery and use the later model resistor.

 

While the why still alludes me, I successfully transplanted an 04 blower assembly into my early vin 03 and have a fully functioning climate control.

 

IIRC, the full voltage goes into the resistor and the output reduced voltage depends on the AC control fan speed setting. Only FULL speed will ' 'bypass' the resistor for full voltage to the fan motor. Other speeds run through the resistor. So it sounds like you are only 'bypassing' the resistor. I don't remember which side of the motor the resistor is on...ground or Pos.... There are also two relays up high on the motor mounting case. And the brown wire is key. Follow the wiring diagrams for each wire. Someone messed with mine and it took a while to track down the faulty wiring (hidden in black tape)...