Heater Problems

[jgulserian]

Hello - I have a 1999 Jimmy and the heater does not work all the time. Additionally, when I adjust from defrost to floor heat it does not transfer or comes out front vents.

 

[Molson02536]

Hello - I have a 1999 Jimmy and the heater does not work all the time. Additionally, when I adjust from defrost to floor heat it does not transfer or comes out front vents.

Check your vacuum hose from the engine on the diver's side to the vacuum canister, then to the fire wall to address the vent selection issue. When inspecting the vacuum lines, take them apart and see if there is any transmission oil in the lines.

The 4wd vacuum switch on top of the transfer-case is known to go bad and leak transmission fluid throughout the vacuum lines and in to your vent selection switch, which is a vacuum selection switch it self.

As for the heater issue it self, try flushing out your coolant with http://www.prestone.com/choose?next=index.php coolant flush and replacing your thermostat also with the OEM rating of 195".

If your heater hoses are both hot to the touch once the engine is up to operating temperature, your going to have to replace your heater vent actuator. You can replace after you take your glove compartment out and it will be on top of the heater duct.

Good luck and keep is posted. Here is 2 links for you to read.
http://gmcowners.com/gmc-forum/showthread.php?t=15262
http://gmcowners.com/gmc-forum/showthread.php?t=16185