Solved!! At least for now.

I need some help from the hive mind. I inherited a C6 (with 9700 miles on it) at the beginning of the year. When I got it it had some pretty significant issues and was shipped across the country as it was in "limp mode" and could even pull out the driveway where it had been stored for many years in the garage. My local Chevy dealer had the car for a week and found a lot of wiring had been eaten by rodents. They patched up the wiring and then told me the TCM was shot and they can't get one so I should come and fetch it. Long story short I got somebody to replace the TCM with a refurb and the car is running.

Now on to my issue with the HVAC. For a while the AC would blow cold intermittently which I put down to needing a regal which I took it in for. They added a half pound to bring it up to spec and it blew cold during the test and on my drive home. A day or so later I get into the car and it doesn't blow cold anymore. I take it back to the shop and they say there's a slow leak on the high side and we need to replace a pipe. 500 bucks later I get a call and they say after the pipe replacement it still didn't work so they replaced the HVAC relay and still no joy BUT engaging the compressor clutch from the OBD equipment and it works. Their conclusion is there is no call for the compressor clutch from the HVAC module and I need to source once as GM stopped making them.

Now before I go and blow another $500 what can I check to make sure that a new HVAC module will actually fix the AC? I know my way around a multimeter but I have no idea where to start? Anybody got some ideas or the wiring diagrams for a 2005 base model c6 for me to work from? Anybody in the Raleigh NC area willing to help me out maybe??

 

The attached PDF is from a 2007 model, but should be no different for your 2005.

Good luck on your diagnostics and be sure and update this thread with what you learn and the resolution so others may learn from your experience.

GD

 

Thanks for that. It was about to be very useful to me until I was checking all the fuses and relays and noticed that if I pushed down pretty hard on the HVAC clutch relay that it relay engaged. I let it go and it would stop again. I swapped the relay out with the horn one and same thing. Works if I push hard on the relay and stops again when I release it. I pulled the whole fuse/relay section out of the fuse box (under the hood) and just checked all the wiring was not snagged on anything and the middle bunch of cables was very taught. I pulled up on the cables a little and reseated everything, put the fuse box back together and tried the A/C again and no joy. I leant on top of the fuse box to try and see if the clutch engaged and as I lean on it I hear a click and the clutch engages. So my conclusion is I have a dodgy joint/connector in the middle section of my fuse box where the HVAC relay is and now I'm looking for instructions on how to open this up and check it out. In the meantime I have everything closed up and I gently pulled up on the middle cable again and it seems to be holding but I just know I'm once pothole or speed bump away from having to pup the lid and fiddle with the wiring again. On the bright side I am not looking for a new HVAC control module.

 

You probably have some burned or dislocated fuse box pins underneath the top fuse panel. There are four bolts that run down the middle and secure the top & bottom sections of the fuse box together. Separate the box and look for burnt or pushed in pins where the connection is lost between the two sections. You should be able to straighten and pull them out enough to connect. PIC of the bottom section with burnt pins is below. Good luck & let us know if this helps...GD