So I have heard from different people all kinds of different stories about why you shouldn't and others say it doesn't matter. So does it harm anything having your AC on with heat?
Mine as well, I had just heard before that it fubars the condenser. Wiki quote: A condenser unit used in central air conditioning systems typically has a heat exchanger section to cool down and condense incoming refrigerant vapor into liquid, a compressor to raise the pressure of the refrigerant and move it along, and a fan for blowing outside air through the heat exchanger section to cool the refrigerant inside. A typical configuration of such a condenser unit is as follows: The heat exchanger section wraps around the sides of the unit with the compressor inside. In this heat exchanger section, the refrigerant goes through multiple tube passes, which are surrounded by heat transfer fins through which cooling air can move from outside to inside the unit. There is a motorized fan inside the condenser unit near the top, which is covered by some grating to keep any objects from accidentally falling inside on the fan. The fan is used to blow the outside cooling air in through the heat exchange section at the sides and out the top through the grating. These condenser units are located on the outside of the building they are trying to cool, with tubing between the unit and building, one for vapor refrigerant entering and another for liquid refrigerant leaving the unit. Of course, an electric power supply is needed for the compressor and fan inside the unit. So in theory I can see how it might cause damage, by over heating or dissipating more heat inside the engine-cab. Or causing the coolant to loose some of its thermodynamic properties, and it will need to be recharged more often. This is of course in theory.....
The factory designs it such that the AC core is first and the heater core is second. The AC acts as a drier to dry the incoming air. Then the cool dry air hits the heater core to get hot. Now this HOT and DRY air hits the windshield and de-fogs it. With out the AC part, you would have a hard time drying off the windshield with hot MOIST air. It'll work, but it will take longer and if you cant take the heat and turn the temp down, dont expect your windshield to clear up. This also works great when you have the AC on with normal heat as you will keep your vehicle nice and dry. Also, not running the AC system is bad. The oil inside the system will seep off of the rubber parts and the refrigerant will be able to escape via the un-coated rubber parts. The more the AC runs, the better. So dont do like the guys on NASIOC in PRoN and disable the AC-Defrost switch.
I've always found that unless my AC is running when my heat is on, my windows fog up. On drier days its not so much a problem, but if its rainy and cold, my AC AND heat are on.
Yep. AC systems remove moisture from the air. Hence the evaporator drain tube located near the down pipe.