AC/heater mode control problem

Tiny
BILL REAVER
  • 2006 GMC SIERRA
  • V8
  • 2WD
  • AUTOMATIC
  • 106,579 MILES

On my 2006 GMC Sierra the a/c heater mode stays on vent even when changing the control to the floor or defrost positions. Also the highest fan speed does not work, all other speeds are ok.

Do you
have the same problem?
Yes
No
Saturday, December 18th, 2010 AT 6:21 PM

4 Replies

Tiny
MIKE4652
  • MEMBER

Its your control unit I belive. Same thing happened to one of my friends 2008 chevy tahoe. You should try that.

Was this
answer
helpful?
Yes
No
Saturday, December 18th, 2010 AT 6:38 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
  • 68,398 POSTS

I need you to check a couple things. First, check if there are vacuum leaks under the dash. The air flow vents are actuated by vacuum. If there is a leak, this can happen. Next, as far as the fan speed, I would recommend checking the blower motor resister.

Let me know what you find.
Joe

Was this
answer
helpful?
Yes
No
Sunday, December 19th, 2010 AT 1:12 AM
Tiny
BILL REAVER
  • MEMBER

Joe,
Thank you for your quick reply.
Where would I look for the vacuum lines under the dash? When I look under the dash no vacuum lines are visable. If it was a vacuum leak wouldent the the engine be running rough? There's no roughness that I notice.
Also a few monthe ago I was running the a/c heater blower on high speed when I started noticing a (electrical) burning smell, then it quit. The blower works on all other ranges but just not on the high speed. Could this be the resistor? Where would I find the resistor.
Bill

Was this
answer
helpful?
Yes
No
Sunday, December 19th, 2010 AT 4:37 AM
Tiny
JACOBANDNICKOLAS
  • EXPERT
  • 68,398 POSTS

I have attached schematics for you to review. The GMC model uses electric and not vacuum for some reason. Review the schematics to see if you can identify where to check under the dash. Also, as far as the high speed, it believe it is a relay rather than the resister. See schematic.

Was this
answer
helpful?
Yes
No
Sunday, December 19th, 2010 AT 11:14 PM

Please login or register to post a reply.

Other Heater Questions