fred 2/27/2012

1998 GMC C1500 Sierra SL 6Cyl4.3L - Engine

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HEATER BLOWS OUT HOT AIR WHEN ON LOW SETTING COLD AIR ON HIGH SETTING

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  jdl 2/27/2012

  Maybe you have sufficient flow through the heater core? With it on high are the heater hoses hot?

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  fred 3/1/2012

  one hot one cool, ac wont shut off,running all the time.

  

  jdl 3/1/2012

  Is your compressor running?
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  fred 3/1/2012

  yes,took ac relay out , have heat on high now. but which switch should i replace?

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  jdl 3/2/2012

  You shouldn't have ac unless the hvac control is set on ac. Any applicable trouble codes?

  

  fred 3/2/2012

  just for O2 sensor, ac button on control panel turned off ,