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Hi All! I'm new here. For my first post I've got a mystery involving a non-working climate control system in which all the relays and fuses test good, the blower motor works, the speed selection dial works (therefore the resistor also works), and yet I have no climate control whatsoever.

So first off, the truck sat for a few months while I ditched the 6.4 turd that I spent $7k rebuilding last fall due to cracked rings on cylinders #7 and #8 only to have the lift pump fail and take out the all-new fuel system ~6k miles later. Anywho, I decided to put a 12-valve Cummins in it because I value ease of maintenance, fuel economy, and, most of all, reliability. In the end, even the deleted, single turbo'd, rebuilt 6.4 couldn't deliver on those. But that's not why I'm here.

Prior to the 6.4 fuel system going down, the climate controls worked exactly as they should. AC blew cold, recirc worked, the air came out wherever the dial indicated it was supposed to, and the fan worked on all four speeds.

Fast forward six weeks, and one Cummins swap in my time off from running my pressure washing business and finishing my last term of college, and the truck fired right up but had absolutely zero climate control functionality. I used the swap kit sold by DCS, which included a conversion engine harness to connect the 12-valve and a few of its key sensors to the original PCM, but no wiring was modified inside the cab, aside from punching a hole in the firewall to install some gauges. I found some of the wire diagrams posted here on the forums and was able to use them to identify some of the wires that plug into the back of the climate control module (below the stereo). I discovered that if I ground out the purple w/green stripe wire the fan runs and I am able to select the speed with the leftmost dial, but I still have absolutely zero control over where the air comes out or what the temperature is.

I tested the appropriate fuses under the hood and down behind the passenger kick panel in the SJB, as well as the blower motor relay, all of which turned out to be okay. The climate control module itself is okay because I swapped out a known working unit with no change.

As far as I can tell, my issue must be in the wiring between the 26-pin plug on the back of the control module and wherever those twenty-something wires go.

My question is this:

Does anyone know how I can test these wires? I need to know where I can find all the other ends of these wires to test for a short. Although, since it seems everything in these trucks has some degree of PCM involvement, I figured perhaps there's a chance someone might be able to confirm that or point me in a more efficient troubleshooting direction.

The wire diagrams are great for showing how the circuit is assembled, but they are worthless when it comes to indicating whether a certain wire should have resistance or voltage, etc.

Miscellaneous (possibly helpful) info:
-I have yet to recharge the AC system post-swap. Since the lines are just sitting until I can adapt them to the Cummins AC compressor, the lines have no pressure in them and the compressor plug is unhooked to prevent accidentally engaging the magnetic clutch and running it without lube. Is there possibly a system-wide emergency HVAC shutoff in the computer that turns off the climate controls when the pressure switch shows no line pressure? (I'm just spitballing here).

Any and all insight is greatly appreciated. This truck is emptying my wallet and I'm eventually going to run out of hair to pull out.

Thanks!
-Jacob
 
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