AC low side over 100#

[raydav]

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.

[Tim]

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

[raydav]

Are you assuming it is just overcharged?

[Tim]

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

[raydav]

What is 121?

[bohica2xo]

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?

[raydav]

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.