With my 2nd gens, the a.c. would be on when in defrost - but not if I had the fan control set to zero. Im not sure the 3rd gens are wired that way.
Basically the heater and a.c. controls are set up on purpose, to have the a.c. running when the lever is in the defrost position and you have the fan control on any position except "off". The reason is to give the a.c. compressor some use during the months of the year when you wont be using the a.c. to cool the interior. This gets oil lubing the shaft seal inside the compressor, and extends its life dramatically' i.e. its done on purpose. Most folks arent even aware the a.c. works when you are using the defrost function.
If you went 6 months without using the a.c. compressor, it would likely start to leak after 2 or 3 years - instead of maybe lasting for 8 to 10 years.
To defeat it I think you would need to add a switch in the line going to the compressor.
I wanted to add that A/C helps the car defrost the INSIDE. The outside, not so much. If Ice is your issue, ac will hurt, but if the interior is moist, ac will help you. You just need to move the temperature lever more towards full hot.
is your A/C really good, or your heat really bad? Ha ha
Maybe a coolant flush is what's really best right now. I avoid the defrost and a/c issue in most cars by moving the lever to feet only, and inch it over until I get some airflow on he windshield, and more on my feet. Or vice versa, whichever is a good blend with no a/c.
I smoke so biasing towards the floor with a high fan speed ventilates the car best as far as smoke odor is concerned. The draft blows smoke everywhere, instead of out the slightly cracked window. But if you have moisture, your shoes and carpet may be wet, and contributing most to humidity. You can get away with some defrost, good dehumidification, and no A/C this way.
the puddle that forms under cars with the a/c running is a testament to how much moisture the a/c removes.