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GM heater help needed

Discussion in 'Uncategorized Threads' started by Cooper, Jan 7, 2008.

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  1. Cooper

    Cooper TS Member

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    This is a trap related issue because this is the vehicle I use to transport myself to and from the trap club! I have a 1998 GMC Jimmy SLT. For the last few months I have not been able to regulate the temperature inside the vehicle, the temp control mixer seems to be stuck on hot. The fan works O.K., the vent selector works O.K. and the inside or outside air selector works. Even when I run the AC the air stays hot. I replaced the heat sensor found in the duct work and it didn't fix the problem. To regulate the temperature is there a flap in the duct work to mix hot/cold air or is the coolant regulated at the heater core? The diaphrams I can find under the dash seem to be working but I wonder if I'm not finding the right one. If there is a diaphram that controls the temp mix what color is the vacuum line? I know there are some good wrench turners on this site so any help would be appreciated.Thank you, Cooper
     
  2. 1Ljutic1

    1Ljutic1 TS Member

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    Had the same problem a few years back. I took it to the mechanic and he fixed it for $50. It was even the GM dealer mechanic! Saved me a few hours. Steve
     
  3. maclellan1911

    maclellan1911 TS Member

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    Electric blend door motor on top of the heater box, possible access through glove box? I personally have not seen to many of these fail? I have replaced a lot of control heads(dash controls) on gms. A scan tool that can communicate with body control/heater control PCM may help narrow your search. I am assuming you have automatic climate control?
     
  4. Cooper

    Cooper TS Member

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    Jan 29, 1998
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    The only things I see behind the glove box are the flap for outside/inside air selection and the controls for the vent selection(floor/window defrost/upper vents etc.) The car does have climate control, If I knew what color the vacuum hose off that control was I could better trace the problem. I will work on again this weekend. Thanks for your help, Cooper
     
  5. cmptrwz1

    cmptrwz1 TS Member

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    Jan 29, 1998
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    HI cooper the problem sound like the heater water control value that controls the flow of water to the heater core is not wroking right if you turn the a/c on the control value shut off the water from the engine to the heater core via heater hoses which then let's the a/c get cold and work in reverce went you want heat the value is vacum controled and it's in the engine compartment on one of the heater hose that goes to the heater some times it's in between the hose and some times it is located on the intake manifold were the heater hose hook up to the manifold it looks like a L fitting with a vacum diaphragm which has a vacum hose going to it that control the flow of hot water to the heater core it sound that the value is stuck open and that is why you only get heat coming out went the a/c is on the value will need to be replaced.If you do replace it do it went the engine is cold because the water/anti freeze will to hot and you mite get burned also you have to drain so water out of the cooling system so you can take the heater hose off to change the value and then refill the cooling system.on some modles thay located the value near the heater core on the inside of the truck it look the same hose going to it and then to the heater but on your modle I think it's on the manifold so you will have look for it.Hope this helps Mike
     
  6. maclellan1911

    maclellan1911 TS Member

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    <a href="http://s160.photobucket.com/albums/t196/jrm7800/?action=view&current=7893651198jimmyheaterboxwithECC.gif" target="_blank">[​IMG]</a> Maybe this will help. You may have to pull dash back to access?
     
  7. maclellan1911

    maclellan1911 TS Member

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    How did you make out?
     
  8. Cooper

    Cooper TS Member

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    Jan 29, 1998
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    I havn't had a chance to work on it again. I removed the bottom plastic covers from the dash last weekend but got hung up trying to get the ash tray out. I was going to finish this weekend but the nice weather keep me out of the garage today and tomorrow I won't have any time. Being winter in Ohio I figure I have a couple of months before to much heat becomes a problem!
    Thanks for your help, Cooper
     
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