I think you have two issues. The AC should work when the defroster is on and when you have the AC on. The most common reason the compressor will cycle like that is when it is low on freon.
As far as the heater, I need you to check something. Start the engine, let it get hot, have the heater on high, and feel both heater core hoses to see if they are both hot. Also, I need to know if the engine is running at a normal operating temp.
Let me know.
Joe
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Thursday, January 7th, 2010 AT 6:49 PM