Automotive Air Conditioning Information Forum

I have a 73 Mustang Mach 1. I got the car about thirty years ago. It had AC stock but I got it with no engine. So I pieced the AC together and charged it with R12. I got a 30# cylinder back when it was available. I still have about half of it.

The car has not been used much the last few years. I am prepping it for a road trip. I assumed I would need to charge the AC. The compressor cycles by a temp switch in the evaporator. When the clutch is disengaged both gauges read about 150#. When the clutch engages low side drops but stays well over 100#. It is blowing cold air. The engine idles at 1K RPM. When the clutch engages it drags the engine about 200 RPM.

I piece together AC systems. I have no way of determining proper charge by weight. So I charge until the low side is 30#.

So why is the low side so high? I have difficulty believing that I massively overcharged many years ago, and it has held.

I am in the process of replacing all my old compressors with 508s, but have not yet scheduled this one.

Pull a vacuum and charge with 24 ounces of 121. Then post pressure readings.

Are you assuming it is just overcharged?

Can't tell what's going on without proper refrigerant levels and readings.

What is 121?

121 is a typo. He meant to say R12.

Are the handwheels on the gauge set closed while making your measurements?

What does the high side read while the low side is at 100 & the system is running?

I now think many of my issues were a short between the headsets. But I decided an update was in order. I replaced the original compressor with a 508, made and/or adapted a few hoses, and all is well.