I have a HVAC problem that is difficult to explain. It all started when the AC would not come on; the LED would light for about 3 sec, then go back off again. Just when I was about to take it in to the dealer (hate to; no warranty), I decided to check the DTCs. I found the following error codes on the DTC for the HVAC (99):

U1064 - Loss of communication with PCM
U1096 - Loss of communication with DCM
U1106 - ????
U1255 - Serial Data Line malfunction

So, I decided to clear the codes and try the AC. It worked!! Joyfully, I drove around town for an hour or so, and stopped for gas. When I cranked the car back up and went for the AC, it was busted again! Then and there I decided to clear the codes again. This time, the message I got for HVAC (99) was "No Comm." I tried a couple of more times, but still the same "No Comm" message. The next day I went out to the garage, checked the DTCs again, but this time I got the same codes as listed above! After a couple of experiments, here is my theory. There is something that is heating up, causing the HVAC to lose communication with the main system. I determined this be letting the car sit in the hot sun without cranking it, and I get the "No Comm" error message. Only when the car is cool and sitting in the garage do I get communication with the HVAC and codes that I can clear.

So, gurus of the C5 underworld, any thoughts? Anything I could check/replace that would save me a few hundred $$ ?

Many thanks in advance,

robrobs

 

Control head is shorted... New control head is the fix.

 

Thanks. Is this a DIY job or can I replace it (I'm pretty competent with good instructions)? Since I don't have a service manual as of yet, are there any instructions out there on how to replace it? Any idea on the price of this puppy?

robrobs

 

It is not hard, just have to remove the center console piece. Few screws. Try http://www.gmpartsdirect.com for cheapest price. Our 99 had 3 units put in under warrentry. I can copy pages from manual, scan and e-mail if you run into trouble.

 

If you want the best price for the part, e-mail greg472@bellsouth.net

Greg is a forum member and works for a Chev dealership. He got me a temperature actuator/motor for my dual zone a/c for $15.00 less than GMPartsDirect and his price included shipping via UPS to my door (their price did not include shipping). I also purchased a headlight motor from him and saved major bucks. All parts were new in the box GM or AC Delco.


[Modified by redriverjohn, 11:15 PM 8/28/2002]

 

Think I paid 200 for the last one. Just follow shifter swap directions for trim bezel removal. if you have a manual trans that is... Just plug and swap very straight forward.

 

Would a loss of communication with the HVAC module cause a loss of communication with the TCS module?