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AC low side over 100#

Posted: Thu May 03, 2018 9:11 pm
by 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.

Re: AC low side over 100#

Posted: Fri May 04, 2018 7:31 am
by Tim
Pull a vacuum and charge with 24 ounces of 121. Then post pressure readings.

Re: AC low side over 100#

Posted: Mon May 07, 2018 8:25 am
by raydav
Are you assuming it is just overcharged?

Re: AC low side over 100#

Posted: Wed May 09, 2018 9:48 am
by Tim
Can't tell what's going on without proper refrigerant levels and readings.

Re: AC low side over 100#

Posted: Wed May 09, 2018 5:08 pm
by raydav
What is 121?

Re: AC low side over 100#

Posted: Thu May 17, 2018 4:53 pm
by 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?