I have a gmc yukon , front a/c works fine, thou the rear a/c does not blow cold air. The fan still works thou once engine is heated up, rear air blows heat.

Blend Door Actuator Replacement 1999-2007 Chevrolet ...

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https://www.youtube.com/watch?v=Eqf-H3COtSo
Nov 4, 2013 - Uploaded by 2CarPros
My problem in my 2004 chevy tahoe is that it will not blow out of the dash or ... onto the vent door gears ...

GMC Yukon AC and Heat Questions - Car Forums at Edmunds.com

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Jul 20, 2010 - 30 posts - ‎16 authors
I just don't get why that doesn't work right in the first place. ... I have 99 Yukon that has a problem with the front air. .... $55,000 for my GMC, I guess expecting cold air when we push A/C and getting 90 degree blast ... 2001 Yukon XL 1500 Front heat & air fine, rear ac blows hot as if heater is on in all settings. More results from forums.edmunds.com

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

I have a 2000 GMC Savana Van SLT with front and rear AC/Heat. My front would blow hot while the rear blew cold with AC on. It turned out to be low on Freon. It's hard to know if you have the right amount of freon installed because pressures vary depending on the ambient temperatures. So the best way is to remove all the freon then reinstall the recommended amount as listed on the evaporator housing near the firewall. This worked fine for me... works like new after installing the correct amount of freon.

There is a climate control module in the head liner of that vehicle. IT needs to be checked or replaced

Rear heat not working ? The blower motor isn't working ? No air coming from the rear vent's ? Is it just a yukon or XL or denali ? What size engine ? 4.8 , 5.3 or 6.0 l Manual or automatic climate control ? Does the blower motor work on any speed ? The front an rear heater system are seperate , have there own electrical circuits . Could have a couple of different systems ,could have a control processor or relay's an a resistor block . Do you know how to test automotive electrical circuit's using a wiring diagram and a DVOM - digital volt ohm meter ? Plus to get at the rear heater-A/C unit you would need to take the right rear trim panel off .
2003 Tahoe No Rear Heat Fix Suburban Yukon XL Repair

Sounds like a bad blend door actuator. That's the motor that diverts air between the heater core and AC

Does the front blow cold ? Diagnosing rear problems
Taking to a qualified repair shop an having it diagnosed would be your best bet >

If you still get cold air out of the rear vents but the front only blows hot air you may have a bad temp door actuator in the dash, it may be stuck on hot and not able to move to cold air. However if you are low on freon with a truck that has front and rear ac then there will be a temp diff between the two. If it is hot air out the front like the heat is on then you have that actuator problem but if it is cool air about the same as the outside air temp then you may be low on freon.

first off make sure you have no blown fuse. but front blower motor may be bad. if it does not work in any speedyou can check for power at the wires going to the blower. under dash on passenger side

check you antifreeze level and make sure its full