Question about 1999 GMC Jimmy

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Heater isn't working (blowing cold air)....and it's overheating as well. Tried flushing heater core but that didn't help. Truck is running rough too. Any ideas as to what the problem might be?

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Check for a thermostat that is stuck open and will not let the block warm up when running,if it can't warm up to operational temperatures,it will tell the computer to keep the fuel/air mixture rich and this will will make it run rough, like having the choke on partway in an engine with a carburetor controlled engine

Posted on Feb 07, 2010

  • danny Hendrickson Feb 08, 2010

    also,these are double cross flow radiators and plug very easily due to the small tubes used in the radiator core,check that the fans are running when it overheats or the block feels warm,maybe a radiator fan sensor in the block is bad and not starting fan

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To troubleshoot this types of problem,click the link below :----http://howtobyme.blogspot.in/2012/02/heater-blows-only-from-defrost.html
--------Go through the procedure to confirm the issue.

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Engine Overheats and heater blowing cold?

http://howtobyme.blogspot.com/2011/11/engine-overheats-and-heater-blowing.html

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http://schematicsdiagram.blogspot.com/2011/12/heat-blows-cold-on-drivers-side-and-hot.html

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This will help.Thanks.

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