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My ac control unit blows cold but when I roll the temp control to gain heat I don't get any heat. Any thoughts?
Thanks
Bob
 

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Bad aux water pump which is not sending coolant to the heater core, or a non functioning heater core valve which is not allowing the hot coolant into the heater core.
 

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Bad aux water pump which is not sending coolant to the heater core, or a non functioning heater core valve which is not allowing the hot coolant into the heater core.
I would say the latter is far more likely, aux pump failures are fairly rare, although certainly not unheard of.
 

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With a bad auxiliary pump, you should get some heat eventually, with a bad valve, you won't.
 
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