00' yukon xl no heat in front but works fine in back

Hey Dan, this is not for your yukon, BUT - its a great diagnosis guide for GM A/C systems...
1995 Chevy Van G20 Heat Blower Fan Repair ZEDIC COM

Blend Door Actuator Replacement 1999-2007 Chevrolet ...

? 2:25
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

forums.edmunds.com > Chevrolet > Chevrolet Suburban

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

The 4x4 actuator in the front differential may be bad. The older heat actuators were notorious for failing, but when the electric actuators came out they got much more reliable. But that doesn't mean they are infallible. Have it checked.

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 >

ac on a 2005 gmc yukon not blowing and cant here compressor the rear ac of the truck is working fine, are there any fuses i can check?

suspect tempreture sensor on drivers side. it seems to send a signal that this side of the car is too cold.

if you have duel setting so driver can control both sides at same time set also to air and see if it jumps to heat on both sides, if so there seems to be an electical problem with the tempreture contoler.

check and make sure the duct work going to the rear vents are attached and in good condition