Q: How defroster works when there is no ac

The normal operation of the defroster is for the outside air is drawn into the a/c heater inlet with the system in the defrost position. When the system is in the defrost position the a/c compressor comes on and the air is drawn in and sent through the a/c evaporator to remove moisture from the air before it is sent through the heater core. Once the air goes through the heater core it then is sent to the windshield as warm dry air that will clear the window of fog for you. Since the a/c does not work the air still follows the same path but now when the air goes through the a/c evaporator the moisture is not removed from the air and after the air goes through the heater core and hits the windshield as warm moist air. This warm moist air will cause moisture to collect on the inside of the windshield and form droplets of water. It will not clear the window of moisture and may make fog worse. It will still melt ice off the outside as before.