Auto Air Conditioning & Heater Repair: car a/c, insulation tape, heater core

Question
i have a 1990 mustang the compressor kick on and the a/c line get cold going into the car put the air is still warm

Answer
James,
This could be a couple of things. The first being that your system is low on refrigerant. While the line may be cold, it may not be cold enough. Check your pressures and this will tell you whether or not you need to add some.
The other thing that comes to mind is your blend door possibly being stuck inthe slightly open position. Your blend door is the door that separates the heat from your heater core and the cold from your evaporator. If this is open even the slightest bit it can counteract the cool air that you are wanting. This could be caused by a couple different things. The first is that your door actuator may be weakening and not allowing it to close fully. Or you could have foreign matter or a strip of the insulation tape that seals it separating and causing it to be slightly open. Or the vaccuum line that connects to the actuator has developed a pinhole leak and is not allowing the full vaccuum to be pulled on the actuator.
The first check though should be your pressures, don't go digging around with the actuators until you are certain your charge is correct. Getting to the actuators can turn into a time consuming process.

Thank you for the question, I hope I was of some assistance. If I can do anything further during this process, or in the future, please do not hesitate to ask. If you found this response to be of some assistance, please remember to rate this answer. Thanks again and good luck in everything.