AC will freeze you but defroster willNOT get warm

2000 4Runner. A/C will freeze you out but when trying to use a/c in heat or defrost mode it will not get warm. I have replaced the control unit but still the same.
What might be causing this?

 

Could it be a bad thermostat?
I have not had this in our 4r but in other trucks, if the thermostat goes out the engine takes forever to get warm & barely blows warm air.
The 4r may be different. This is my guess.

 

Welcome to the forum from Nebraska.

 

So, you are saying that if you put your car on defrost, and turn up the heat, there is air coming up through the vents under the windshield but it never gets warm IF the AC is on? If the AC is off, everything works fine?