My daughter has a 1999 gmc sierra. Heater and air cond. work fine and So does the blower motor work on all settings. It will blow air to the floor and insrument panel just no air to the dash to defrost the windshield.What could be the problem
2007-01-12 12:05:42 · 4 answers · asked by James Dodge Boy 3 in Cars & Transportation ➔ Car Makes ➔ GMC
You either have a jammed door, that is something like a pencil jamming the door, or you could have a door stuck by a liquid spilled into the dash that has stuck the door to the duct. These HVAC systems are fairly simple, but extremely hard to get at. GM has gone away from individual vacuum actuators for each door inside the old HVAC to a one motor electric drive that powers several of the doors to proper positions. You will have to start by inspecting what is going on. You say that the other modes are working so I will assume that something is jammed or stuck or the motor has lost its memory. This has happened to me with several of these trucks. What I did to relearn the memory was drive the motor as far as it could go one way. Then I would uplug the AC control head and the motor drive and let them sleep for ten seconds or so. Then reconnect both and try driving the motor from far end to far end to set the sensor voltages inside the control head. This often fixed most of the trucks. There was some that required a new motor however and this is not a fun job as it is located somewhat behind the dash. Check for obstructions as best you can as this is the most common problem. Good luck.
2007-01-13 04:13:56 · answer #1 · answered by Deano 7 · 0⤊ 0⤋
Look for holes or a disconnected hose going up to the dash/windshield.
2007-01-12 23:58:35 · answer #2 · answered by Jerry B 1 · 0⤊ 0⤋
Mode door actuator is bad or door could be broken.
2007-01-12 20:41:11 · answer #3 · answered by TonynNC 5 · 0⤊ 0⤋
the flap inside the vent is getting jammed!
2007-01-12 20:29:15 · answer #4 · answered by italianpanther7 4 · 0⤊ 0⤋