Chevrolet Repair Questions? Ask a Chevy Mechanic for Answers ASAP
Welcome, I'm Chris (aka-Moose).
The HVAC system and EGR system are 2 different concerns. What sound did the defrost usage make and was the air flow actually coming out of the defrost or elsewhere?
When using defrost, the AC turns on because you need dehumidified air on the glass to remove the fog inside. I believe your rpm and noise concerns are due to a AC compressor concern. Unplug the AC compressor and try defrost again to see if that concern is now resolved.
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Hello, Chris here again,
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