Hello Gents. Here is my problem. I have a 01 GT with 170,xxx miles. I have 2 problems. 1st problem is I have no heat. I have replaced the thermostat, and flushed the heater core, as well as check for coolant leaks from the top to bottom and front to back of the car and found nothing leaking. Coolant is full and bubble free. The 2nd problem is when I have the control setting turned to defrost it blows ICE cold air through the defrost with the tempiture knob set to hot. I understand that the compressor is suppose to run in defrost for air drying purposes. What would make the a/c blow when it is set to defrost in the hot position??? Blower blows through all selections when knob is turned and you can feel a slight change in tempiture and a audible change when the tempiture knob is turned
I would explore the possibility that the heater blend door has an issue. In the Mustang the temperature knob is connected to a series of push/pull flexible jacketed cables. These in turn rotate a bell crank of the heater blend door. IF the cables have become disconnected or the bell crank is broken this could leave the blend door closed. The result would be no heat.
If the AC/heater mode controller is removed from the dash the cables are easily visible. Work the cables through their range of motion and trouble shoot from there.