My m1200 16 seer havc unit when in defrost mode why does the fan blow cold air only

i had a new m1200 16 seer ac/heat pump unit installed but the defrost mode comes on and the fan only blows cold air

The idea is, your windows frost from a difference between air temperature inside and outside the car, so when you have the defroster on, it blows the air at the windshield from outside the car, it doesn't heat or cool it. The idea there is it is trying to heat or cool the inside of the windshield to match the temperature it is outside the car, this will get rid of the frost. Do you see what I'm saying?