Cold air in front not in the rear. Could be several things. If freon level is low, the front will cool but not the back. The rear ac has blend doors to mix cold air with warm, This could be a problem. Also the rear air has an expansion valve that may not be working.
Try to back wash the heater core first if it doesnt work then its clogged up try to turn the heater on the front with the heater off for the back keep an eye on the temp guage if it goes up than normal then its clogged....
Fyi u have to run the engine for awhile with the heater fan on
SOURCE: rear heat in 2004 gmc
I have a 2006 yukon and have had to replace the actuator in the rear heat/ac twice. It moves a valve that closes the cold/hot ducts. It is a cheap defective part/design.
SOURCE: 2002 GMC Yukon front A/C blowing warm air
Here is a TSB (Technical Service Bulletin) for your vehicle for loss of temp control.
File In Section: 01 - HVAC
Bulletin No.: 01-01-39-007
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
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 miss routed in the instrument panel carrier may cause these conditions.
If the warranty campaign is over i am sure they can or may have in the system on how to correct the problem.
Good luck and hope this helps, keep me posted if you need help on to the repair procedure.
SOURCE: Air Conditioner Problem
the most common problem here is a defective air temperature control blend door actuator, this is what moves the door that controls air flow across the heater core or the ac evaporator core, to replace this requires u remove the dash assembly.
Testimonial: "good"
SOURCE: Heater fan on 2002 Yukon does not operate in front, only rear.
The front blower motor is controlled by the blower resistor module.This is usually the problem with the front blower not working.I looked up the schecmatics and I don`t see separate fuses for the front and rear.But the fuse for the front blower is in the under hood fuse block.If this is good then The problem is probably the resistor module.It is next to the blower motor.The connector from the resistor connects to the blower motor.If you want to confirm this you can check for power and ground at the blower motor connector when you activating the blower switch on.This can be done with a test light.Make sure you have power going into the resistor module also.If you have power going in and no power at the blower motor then replace the resistor.Hope this helps.Good luck.
SOURCE: 2002 GMC YUKON XL 1500 MOTOR DIES AFTER GOING
Check the fuel cap!! If the vacuum relief is not working it can impede the fuel flow and cause the engine to shut down or not restart after a stop. Waiting usually gives things a chance to stabalize and the engine will restsrt. When this happens again try loosening the cap and see if the engine will restart.....If it restarts immediately, REPLACE the fuel cap..Do Not leave it loose because this will cause other problems. If it is not the fuel cap the problem may be the filter, the fuel pump, or aome other fuel system malfunction.
Testimonial: "Great will try it "
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