Author Topic: A/C system pressures  (Read 336 times)

Offline preaction

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A/C system pressures
« on: May 03, 2017, 12:56:27 AM »
Im working with a 67 system using r12 and after charging the system with about 80% of a full charge, it doesn't want to take the last 20% Im getting 96 to 98psi on the low side and a very steady 175 on the high side, with the air being cooled to 62* I realize I need to get that last bit of r12 in there but are these pressures sound about right ?
8R02S125064- January 6 1968  SJ   7F93S591808 - April 28 1967  Dearborn   7F91S544039 - December 17 1966 Dearborn

Offline 67gtasanjose

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Re: A/C system pressures
« Reply #1 on: May 03, 2017, 05:25:43 AM »
The beauty of the early system is the site glass...if yo see no bubbles passing by on occasion, you are full. It doesn't get any easier than that ;)
Richard Urch

1967 (11/2/66, S.J.) Luxury Coupe, 289-4V w/Thermactor Emissions, C-4, Well Optioned
2005 (04/05) GT Premium Convertible, Windveil Blue, Parchment Top w/Med. Parchment interior,  Roush Body Appointments

Offline preaction

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Re: A/C system pressures
« Reply #2 on: May 03, 2017, 02:36:17 PM »
Thanks Richard.
8R02S125064- January 6 1968  SJ   7F93S591808 - April 28 1967  Dearborn   7F91S544039 - December 17 1966 Dearborn

Offline COSix7

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Re: A/C system pressures
« Reply #3 on: May 03, 2017, 02:46:23 PM »
Those pressures don't seem right according to the manual.  Low side should be between 12-50 psi under normal conditions, high side 80-300 psi (rule of thumb is about 6-7 times the low side).  96 psi is way high regardless of close you are getting to a full charge, assuming your gauge setup is correct.  There's lots of permutations of pressure readings and possible causes but here's a couple from the manual related to the low side reading too high:

Having low side above normal, but high side normal, it often points toward expansion valve problems. Is your expansion valve good and its sensing element installed right and clamped tight? If not, too much R12 flows, and your low and high pressures become closer together.

Having low side above normal, but high side below normal, it often points to compressor weakness/failure.

In the heat of Texas, it seemed like it was always 100 degrees and 98% humidity anytime you wanted to do A/C work or get paint to dry.  On my 67, I always called mine "good" when the pressures were well within ranges, when the bubbles in the sight glass disappeared/reappeared quickly when the compressor kicked on/off, when only the right parts got darned cold, and when the system "cycled" properly without being annoying.  That thing would spit snowflakes out the chrome vents when charged properly!
67 Coupe Sports Sprint 289 2V, 3 Speed
19 June 67 San Jose build
Maroon Met exterior, Red interior with console
PS, Selectaire A/C, AM Radio
7R01C223XXX