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I have an 02 Avalanche with auto climate control. This summer my AC stopped working because my blower would not kick on. I dealt with it, but now its winter and I have no heat, more importantly no defrost, not to mention my 2 month old baby. I have replaced the blower, the blower control module and the hvac control module in the dash. Everyone Ive asked said it had to be one of these 3 things, wells its not. Anyone have any ideas, or experience with this type of problem? Oh yeah, its not a fuse and the wiring in the dash is fine, no burns. Only other thing I can think of is a relay. If you know something I can provide more information on whats been done, thanks. I have an 02 Avalanche with auto climate control. This summer my AC stopped working because my blower would not kick on. I dealt with it, but now its winter and I have no heat, more importantly no defrost, not to mention my 2 month old baby. I have replaced the blower, the blower control module and the hvac control module in the dash. Everyone Ive asked said it had to be one of these 3 things, wells its not. Anyone have any ideas, or experience with this type of problem? Oh yeah, its not a fuse and the wiring in the dash is fine, no burns. Only other thing I can think of is a relay. If you know something I can provide more information on whats been done, thanks. I checked the wiring harness connections and everything is routed the correct way. I have been told that the blk/gry wire coming out of the hvac controller going into the blower control module is 0-4 volts positive. Mine is 0-12 volts negative. How could that just change on its own? I checked the wiring harness connections and everything is routed the correct way. I have been told that the blk/gry wire coming out of the hvac controller going into the blower control module is variable 0-4 volts positive. Mine is variable 0-12 volts negative. How could that just change on its own. Basically… A/C – Loss of Mode or Temperature Control Notes Bulletin No. : 04-01-39-007 Date: June 17, 2004 TECHNICAL Subject: Loss Of HVAC System Mode and/or Temperature Control (Replace HVAC Control Module) Models: 2002 Cadillac Escalade, Escalade EXT 1999-2002 Chevrolet Silverado, Suburban, Tahoe 2002 Chevrolet Avalanche 1999-2002 GMC Denali, Sierra, Yukon, Yukon XL 2001 GMC Sierra C3 2002 GMC Sierra Denali with Automatic HVAC System (RPO C68) Condition Some customers may comment that they cannot control the HVAC system modes and/or the temperature. These concerns may be intermittent. Cause An HVAC control module logic lock-up may be the cause of these conditions. Correction I’mportant: Prior to replacing the HVAC control head, review Corporate Bulletin Number 01-01-39-007. Replace the HVAC control module. Refer to the HVAC Control Module Replacement procedure in the HVAC System – Automatic sub-section of the Service Manual. A/C – Loss of Mode/Temperature Control Notes File In Section: 01 – HVAC Bulletin No. : 01-01-39-007 Date: January, 2002 TECHNICAL Subject: Loss Of HVAC System Mode and/or Temperature Control (Reroute Wiring Harness) Models: 1999-2002 Chevrolet and GMC C/K Pickup Models (Silverado and Sierra) 1999-2002 Chevrolet and GMC C/K Utility Models (Avalanche, Suburban, Tahoe, Yukon, Yukon XL, Denali) 2001 GMC Sierra C3 2002 GMC Sierra Denali 2002 Cadillac Escalade, Escalade EXT Condition Some customers may comment that they cannot control the HVAC system modes and/or the temperature. These concerns may be intermittent. Cause There may be poor terminal contact and/or bent terminals in connectors C206 (RPO C68 automatic HVAC controls) or C296 (RPO C60 manual HVAC controls). Excessive tension on the wires due to the wiring harness being misrouted in the instrument panel carrier may cause these conditions. Correction 1. Remove the Air Bag fuse. 2. Disconnect the steering wheel and instrument panel (IP) air bag connectors. Refer to the SIR subsection of the Restraints section of the Service Manual for connector locations. 3. Remove the IP upper trim pad. 4. Locate connector C206 (6 cavities) or C296 (8 cavities). The connector is attached to a metal brace on the far right side of the IP carrier above the IP air distributor duct. 5. Inspect the routing of the wiring harness to the connector. The proper routing of the wiring harness is above the air distributor duct with no tension on the terminals in the connector. The routing is improper if the wiring harness is below the air distributor duct with excessive tension on the terminals in the connector. The excessive tension may cause poor terminal contact, resulting in open circuits, in the connector. The wires may also pull the terminals out of the connector or pull out of the terminal itself. 6. If the harness is routed properly, contact Technical Assistance for further information. 7. If the harness is misrouted, remove the connector from the brace. 8. Disconnect the connector. 9. Perform a pin drag test on the female terminals. 10. Inspect the male terminals for straightness. 11. Inspect the wire to terminal connection to insure that no wires have pulled out of the terminals. 12. Reroute the wiring harness above the air distributor duct. 13. Firmly reconnect and reseat the connector. 14. Reattach the connector to the metal brace. 15. Reinstall the IP upper trim pad. 16. Turn Off the ignition and reconnect the steering wheel and IP air bags. 17. Reinstall the Air Bag fuse. 18. Turn ON the ignition and verify that the air bag light flashes seven times and goes out. 19. Clear any diagnostic trouble codes that may have been set. 20. Verify proper operation of the HVAC system mode and temperature controls. May this will help. This is GM TSB’s.

Do not try this at home. HVAC training is required. In this video I troubleshoot a Trane BWC150 RTU.


Updated: May 15, 2014 — 11:50 am
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