HVAC: a/c works only on defrost

JeeplessInGB · 08-06-2010, 07:07 PM

Please read before posting that it is a vacuum leak.

My '00 JGC Laredo had air moving only out of the defrost vents. I traced the leak to a hole drilled in the vacuum tank done by the dealer when they put in a new fan relay. (A$$holes.) I fiberglassed the hole and reinstalled everything.

However; the A/C light only comes on when the mode selector is on defrost or blend defrost/floor. If you turn the knob to floor, recirc, panel vents, etc, the A/C light shuts off. Here's the interesting part. If i push the rear window defrost button in hard enough, I can make the A/C light come on regardless of the position of the mode knob.

I've got the dash apart right now, and have located the power/ground for the HVAC panel, but without a diagram, i'm not sure what i should be looking for. I have read of other people having this problem, but none of them have posted a solution.

Please help !

JeeplessInGB · 08-07-2010, 12:15 AM

bump-

Anybody ever hear of this ?
I got it working briefly by pushing the rear window defrost button twice quickly. Shortly thereafter it went back to not working unless defrost button was held in.

Milewsky80 · 08-08-2010, 09:03 PM

Check for a broken/unhooked vacuum line by the firewall in the engine bay. Not sure where to look exactly with the 4.0

JeeplessInGB · 08-08-2010, 11:07 PM

negative. i pressure tested that line. it's solid. this is more of an electrical issue... you have to push down on the defrost button hard to make the AC come on.

e043656 · 02-18-2011, 06:10 PM

I am having the exact same problem - the A/C light only comes on with the knob on the defroster settings, or if I press the rear defog button hard or multiple times.

What did you do to fix yours? I assume a new control panel with the knobs and switches?

RiverMCK · 07-24-2011, 08:56 AM

I'm experiencing the same problem with the wife's 2003 WJ. Anyone come up with a diagnosis?

JeeplessInGB · 07-24-2011, 01:53 PM

Quote:

Originally Posted by RiverMCK

I'm experiencing the same problem with the wife's 2003 WJ. Anyone come up with a diagnosis?

#1, make sure you have the manual climate control. Automatic has a whole other set of gremlins.

#2, pressure test your vac lines for leaks. I had a hole in my vac resivoir box under the pass side headlight that was causing the majority of my problems. If you're a smoker, this is fun. Take a big drag and blow it into the line that comes off the intake manifold. look for smoke rising from random spots in the engine bay. Thats how i found my leak. Don't smoke? Call a smoker or pay $30 for your shop to hook it up to a smoke machine.

#3, if all else is good, buy a new climate control panel. I paid $20 for mine at a yard. My issue was an electrical fault within the panel that would only direct air to the proper place when holding the defrost button. It was wierd. If all of the above fails, PM or email me your phone number.