[Peter7307]

With most a/c set ups the air is first sent over the a/c condenser to make it dry and also cold and then if needed it is sent through the heater matrix / core to add whatever heat is deemed necessary.

Many drivers want both warm air and dry air in a humid environment to defog windows etc.

Also auto a/c compressors are notoriously inefficient due to the operating rev range they are needed to work over.
If they were even close to the efficiency levels in household a/c units they would not last at speeds much above idle.

Pete.