Our 2002 K1500 Suburban only puts out heat when it is accelerating. The rest of time it blows cold air. What could be wrong?
Probably cause would be the water pump. The impeller wears out over time and it's not pumping enough coolant through the heater core at idle. At higher RPM's, more coolant flows. If you ever used any of the stop leak products, it could be that the heater core is clogged.
Check that your coolant is at the proper level as well, if it is low it may only pump enough during acceleration.
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