2004 Jeep Cherokee hea or AC stuck on defrost or off

CLAYTON1931

MEMBER
2004 JEEP CHEROKEE
6 CYL
4WD
AUTOMATIC
84,000 MILES

Hello, I have a jeep grand cherokee and one day all of a sudden I could not change the air flow to select vent, floor, or anything in between. The knob, no matter what posistion is always on defrost or off. The temp knob and fan level knob still work fine. I took the whole assembly out and I believe the problem is not in the knob. I also have checked all fuses. I suspect that there is a vacuum stuck somewhere. Do you have any suggestions? I dont want to pay dealership prices to get this fixed. Thanks.

Tuesday, November 24th, 2009 AT 4:55 PM

3 Replies

BMRFIXIT

MECHANIC
19,053 POSTS

The mode control knob on the a/c heater control panel is used to direct the conditioned air to the selected system outlets. On manual temperature control systems, the mode control knob switches engine vacuum to control the mode doors, which are operated by vacuum actuators. On AZC systems, the mode control knob switches electrical current to control the mode doors, which are operated by electronic actuators need to check for codes

vacuum supply line is connected at the engine intake manifold for the manual temperature control system.

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Wednesday, November 25th, 2009 AT 5:58 AM

CLAYTON1931

MEMBER
10 POSTS

Thanks a lot for the advice. Would an error code come up on the manual vacuum system if something non-computer based was wrong? After the supply from the intake manifold, where does it meet with the accuators? Thanks.

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Wednesday, November 25th, 2009 AT 2:57 PM

BMRFIXIT

MECHANIC
19,053 POSTS

Manual with vacuum will not set any codes and have to check for vacuum leaks
black line under the dash should have vacuum all the time with engine running
check the diagram in the above post it shows how to check

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Wednesday, November 25th, 2009 AT 6:42 PM