Chevrolet Repair: 02 GMC Yukon XL 1500 5.3L (Heater), gmc yukon xl, gmc yukon

Question
Ok, the heater in my 02' GMC Yukon XL 1500 5.3L still blows air but when the dial is on hot it still blows cool. At other times the heater will blow hot air, when set too. What would cause the heater to work sometimes but not all the time?

Answer
MR PETERSON,THERE ARE A FEW THINGS THAT CAN CAUSE THIS. THE HEATER CONTROL HEAD ON THE DASH COULD BE GETTING FAULTY..THE DOOR THAT MOVES TO BLOCK OFF THE HEATER CORE AND EVAPORATOR COULD ALSO BE STICKING..THERE MAY ALSO BE A VACUUM LEAK TO ONE THESE BLEND DOORS. ON MY 2004 CHEVY PICK UP IT TURNED OUT THAT IT WAS THE CONTOL HEAD THAT WAS BAD..THIS IS NOT EASY TO DIAGNOSE WITHOUT REMOVING HALF OF YOUR LOWER DASH. IF YOU FEEL YOU ARE UP TO THE TASK YOU CAN SEE WHAT IS OR IS NOT MOVING WHEN YOU MOVE THE CONTROL PANEL LEVER. I WISH I COULD HELP YOU MORE BUT THERE IS NO EASY ANSWER ON THIS ONE. GET BACK TO ME WITH MORE INFO IF YOU CAN AFTER YOU REMOVE THE LOWER DASH IF YOU ARE THAT IS..WOULD YOU PLEASE RATE THIS ANSWER FOR ME WHEN YOU LEAVE THIS SITE,THIS WILL HELP ME,, THANKS TOM...