Heater hot or cold nothing else

1999 CHEVROLET TRACKER
123,000 MILES • 1.6L • 4 CYL • 4WD • MANUAL
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ZIGGYZ
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  • 1 POST
My car has a heater problem. The temperature is either full hot or full cold. I say cold but it does not have an air conditioning system just the heater and vent. I have traced the temperature control slider cable down to the damper box and it moves the levers and seems adjusted properly. Even if I manually move the lever I never get anything but full hot or full cold. it is random. Moving the lever never makes any difference . it either turns on hot , or cold. some times I hear a thump and I know then it will work. everything else on the heater works fine, blower , re-circulation vent etc., seems fine.
any ideas would be great.
Sep 24, 2017 at 9:03 PM
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STEVE W.
  • CERTIFIED EXPERT
  • 15,118 POSTS
Best guess is a broken blend door inside the case or the shaft sheared at the control. They are plastic and can break. Items tagged with 3 in the picture. I would try removing the cable and see if you can move the door manually right at the shaft. If you have a bore scope you could snake it into the system and look at the doors themselves. If they are broken, it depends on where. I have repaired a couple that the shaft was broken by drilling through the shaft from the end and installing a long small screw coated with epoxy.
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Sep 26, 2017 at 4:35 AM