Mhpautos means, will the inner part of the compressor turn?
The pulley may free-wheel just fine, until the A/C or heat is turned on. Then the clutch locks the pulley to the compressor!
If the compressor is locked up, the pulley cannot spin freely, and the inner part sorta grinds on the pulley.
The reason "heat" makes it engage is because the "defrost mode" uses the A/C evaporator to remove moisture, before the air is blown on your windshield
If you disconnect the wire to the compressor, it should not come on. You may be able to get by a while, and still have heat, until you can get it fixed. Only if the pulley will spin free.
Thursday, October 6th, 2011 AT 5:11 AM