Chevrolet Repair: 2003 Suburban wont blow warm air in rear, c lines, electrical problem

Question
QUESTION: Hi Tom,  I have a 2003 Suburban 1500, 2 wheel drive with about 110,000 miles.  It's an LT with the leather and all the gadgets except the sunroof.  
The rear air will not get hot as of recently when the weather turned cold in GA (at least that's when we noticed, but it worked fine last winter).  The front right and left both work great.  The rear seems to be blowing very cold as if the AC is on b/c I've tested it on different days, including when the weather was 60's and the air was still blowing quite cold.  I have tried using the front controls for the rear air as well as the rear controls but neither change the problem.  I tried disconnecting the battery to reset the computer but that didn't work either.  
I have read a good bit on line and am suspicious that it could be a rear blend door actuator, but I don't know this for sure.  If you think that sounds likely, I'd love your help locating it.  Please let me know if you need any more info.
Thanks so much,
Josiah

ANSWER: HI JOSIAH,WHAT YOU WILL NEED TO DO IS GET THE TRUCK RUNNING AND WARMED UP.GO UNDER THE TRUCK AND CK THE COOLING LINES GOING TO THE HEATER CORE. BOTH OF THIS LINES SHOULD BE HOT.IF NOT AND JUST ONE LINE IS HOT THE HEATER CORE WILL NEED TO BE FLUSHED.REMOVE ONE HOSE AND PUT A GARDEN HOSE TO AND LET FLOW.. IF BOTH ARE HOT,YOU MAYBE CORRECT ON THE BLEND DOOR. IF THIS IS THE CASE YOU WILL NEED TO REMOVE THE PANEL INSIDE TO SEE IF THE DOOR IS STUCK OR SOLENOID THAT CONTROLS IS BAD..BUT FIRST CK BOTH OF THESE HOSES,NOT THE A/C LINES BUT THE HEATER LINES..SOMETIMES THERE IS A BLOCKAGE IN THESE LINES AT THE CORE..LET ME KNOW HOW YOU MAKE OUT,GOOD LUCK,,TOM..

---------- FOLLOW-UP ----------

QUESTION: Ended up taking it to the mechanic down the street.  He diagnosed is as an electrical problem and had to replace some sort of module and also an actuator that the bad module had burnt up.  Almost $400 for the parts alone b/c the module is only available from the dealer.  

Thanks for your helpful suggestions
-Josiah

Answer
HI JOSIAH,YES THERE IS A MODULE THAT OPERATES THE BLEND DOORS BUT I NEEDED TO KNOW IF WE HAD HEAT GETTING TO THE HEATER CORE FIRST. BUT I GUESS YOU DO..SO THE PROBLEM WAS THE DOOR WAS NOT OPENING AND ALLOWING THE HEAT TO INTO THE TRUCK.. IAM GLAD YOU GOT TO THE BOTTOM OF THIS. THESE MODULES ARE NOT CHEAP !!!!THANKS FOR GETTING BACK TO ME..