Question about 1997 GMC Jimmy

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Ca/heater controls **** in vent mode

Ac controls stuck in vent mode. no vacuum to control head. where does vacuum line tap into under the hood?
Comment by schochiometr, posted on Aug 24, 2008 No changes to fuses. I rechecked all fuses and they're good. Comment by schochiometr, posted on Aug 25, 2008 To clarify, I have a 1999 GMC Jimmy, 2 wheel drive. I checked for vacuum at the ac/heater contol and there is no vacuum. I found where the vacuum line comes out under the center of the dashboard to the left of the console. It runs back to the firewall and into a large wire bundle. I can't see where it goes from that point. I've looked under the hood at the firewall and can't see the vacuum line. I'm trying to find the vacuum source to determine what the problem is. Is there a switch or relay I'm not aware of? I have a Haynes manual but it's no help for this problem.

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  • Anonymous Sep 09, 2008

    I have a 1996 gmc 4X4 sle jimmy. I had the same problem, it cost me about $25.00 to fix. I went to my local salvage yard and took out one from another jimmy. Replaced and it is working fine. The problem was not the vaccuum but the switch. The switch is made up of 1 part plastic, 1 part steel ball bearing and 1 part plastic. The steel ball bearing is sandwitched in between. Where the ball bearing rides there are small triangles that increase in size. The more you turn on and off the switch the more it wears out. I hope this fixes your problem.

  • tyoung250 Nov 10, 2008

    I have the same problem, but mine is stuck on defrost and floorboard. I have taken the switch apart, and it's fine. I blow air through the vacuum controls, and all of the dampers operate. There is no vacuum at the switch to control the air directional settings.



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Just fixed same problem with my '98 Jimmy for under $3. The vacuum line comes thru firewall (semi-rigid 3/32" hose) with the main wire bundle just below the brake powerbooster. After about 7" this line goes to the first 3-way 'T' connector with an inline adapter going up to 5-32". Hose 2 from the tee goes to connection on the inside of left front fender. Hose 3 from the tee goes to another 3-way fitting where the system gets vacuum ultimatley from a larger hose going to the plenum where the PCV hose attaches. Check ALL these hoses for rot or splits.

Posted on Jan 17, 2010


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