99 Yukon ac compressor not getting power

[akgriffith]

I've got a 99 GMC yukon SLE. Recently the blower has had a mind of it's own. It will work one minute and not the next, doesn't seem to matter what setting the switch is on. And now the A/C compressor is not getting any power. I have not used the A/C in a while so I'm not sure how long this has been going on. I have tested the relay and it works(switched the starter and a/c relays since they are the same). The light that turns on when you push the a/c button does not come on no matter what. The system is fully charged with coolant. Any ideas on how to get the a/c up and running?

 

[SunlitComet]

See if this applies to you first if not we can run down the system to find your fault:

A/C - Loss of Mode or Temperature Control 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
Important: 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.

---------- Post added at 01:09 PM ---------- Previous post was at 01:07 PM ----------

Also this one as well:

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. Warranty Information

For vehicles repaired under warranty. use the table as shown.

 

[akgriffith]

I don't think those are my problem. The heat works just fine and the hvac system dosen't switch systems randomly. I just can't seem to get power to the compreesor. After a little searching I think I may need to swich out the A/C & heater controls, part #
AC DELCO # 15-72547. Any thoughts on that?

 

[SunlitComet]

How about a freon charge inspection first to make sure you have enough in there. I am not in to just throwing parts at it. But since you fan is acting up to remove the module and inspect the connectors and terminals for electrical damage first. If you light comes on then your head unit appears to be working so it is up to the PCM to determine if it is safe to run the compressor and that involve high, low and cycling switches for proper control.

Please refer to post #6 in the link below for the diagrams to you system to help trouble shooting. Any other questions feel free to ask.
http://www.tahoeyukonforum.com/forum/showthread.php?t=28851

---------- Post added at 02:08 PM ---------- Previous post was at 02:07 PM ----------

Make sure when you turn fan of the a/c goes out automatically but lights up in any other fan speed position.

 

[akgriffith]

I'll pull the module tonight and inspect for damage. the system is fully charged with freon, 55 lbs at low port at 90 degree outside temp.

---------- Post added at 05:09 PM ---------- Previous post was at 04:24 PM ----------

i've had a chance to pull the module, here is what i found.
the light that indicates the a/c is on was just burned out. There does not seem to be any damage or melted wires. i rechecked to freon level just to make sure and it was way too high....over 100 PSI! any idea what would cause such a jump? and still the compressor just sits there doing nothing. bad compressor?

 

[gpracer1]

My light is burned out too. Some day Ill get around to replacing it.

100 psi when the system is off is normal when hot.

It does not matter if you have 2.75 lbs of 134a in the system or 7 lbs.......when the system is not running the pressure will always be the same for a given temp of the freon.

When your can of freon is full, or 3/4 empty, it has the same pressure in the can untill there is no more liquid.

Your 100 psi could mean you have way too much, just the right amount or barely just enough liquid freon in the system....only way to find out is with gauges and ac running.

 

[SunlitComet]

If you have a 100+ psi in the system and the system does not even attempt to engage then either a low pressure switch, cycling switch, clutch or the output signal from head unit to Pcm requesting a/c is not there. With system set to run probe clutch for volts. if not seen then unplug and jumper connectors of low pressure switch (top of compressor) and cycling switch(accumulator on the firewall) one at a time to look for activation. Post results back here.