Electrical Ac Compressor Clutch Is Acting Weird...

The ac clutch is supposed to cycle on and off during normal operation. Are you seeing something abnormal about the normal, intermittent operation or simply unfamiliar with how the system works?

As long as the clutch is engaging and disengaging rythmically, it's fine. The fan will stay on because it's supposed to when the ac is on to draw air through the condenser coil.

Stop by a shop and have them check the system pressure. It's normal for a system low on refrigerant to cool uncommonly well and then not at all when the evaporator coil freezes up.

Did you vacuum test the system? What are your high and low side pressures?

Your pressures will tell you if there's something wrong with the system like being over or undercharged, clogged, etc. The vacuum test is for finding leaks.

Unplug the low pressure sensor and see if the clutch disengages.

For your Model year Mustang the high pressure compressor turn off is 425 PSI.

Also your Model year Mustang will engage the high speed fan at 325 PSI head pressure. When the head pressure drops below 275 the high pressure switch will re-open. However the PCM will hold over the high speed fan for 20 additional seconds. This is done to prevent short cycling of the high speed fan.

Your high side pressure seems a little high to me even for the high outside temperatures. If this were my car I would make sure that the outside coil is super clean. Use a garden hose running water from the front and back. Double check that all fan shrouds and air dams are in place. Double check there aren't any dented AC lines.

But if you know that the high side pressure is not exceeding 400 PSI and you think that the high side pressure switch is the cause, that is very easy to test for. Test the high pressure switch DB/V and DG/O wires to confirm the switch is closed. If the high pressure clutch switch is opening too low (below 425 PSI) this could be your problem.

It helps to know the low side readings as well as the temperature of the cool air coming from the vents. Understanding the low pressure side can help determine IF your AC system is over charged.