R12 pressure? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Mike Bradbury · 07-24-2009, 08:02 PM

I searched the archives for the answer and most dealt with the conversion to 134a. My question is how much pressure is in the '69 truck R12 system? I have a friend in the AC business and he has R12 and the compatible replacement as well, he needed to know how much pressure was in the system in order for him to recharge it. All else works fine just low on charge, I would rather fix it for free rather than convert to 134a for now, I know it will probably be inevitable though.

chevroletrucks · 07-24-2009, 09:47 PM

I'm pretty sure your talking about static pressure, I dont know if you will find a spec. for that? At our shop we either read the gauges (compressor running) or did a complete evac to see how low it was. If memory serves decent typical running pressures for R-12 were 40psi (low side) 200psi (High side) This will vary depending on ambient temperature and humidity.
Hope that helps some?

**El Jay** · 07-24-2009, 09:52 PM

The high side pressure will vary depending upon the ambient temperature.

For example, at 80 degrees the high side pressure should be in the 150-170 psig range.
At 100 degrees, it will be in the 210-230 psig range.
No 2 systems will register exactly the same.
The low pressure side should be between 15-30 psig, again depending upon ambient.

These are just rough examples out of a 35+ year old Motor's Manual.

I know that's not exactly what you were looking for, but I hope it helped you a bit.

Mike Bradbury · 07-24-2009, 10:46 PM

I know very little about the system, so I will tell him this info and hopefully it is what he needs. I think he was talking about with the compressor off, but not sure.

**WorkinLonghorn** · 07-24-2009, 10:49 PM

Maybe he was asking what the R-12 "charge" is ,which is how many lbs. and onces it takes to charge an empty system.
The charge is listed as 3 Lbs.,4 ozs. in the 1969 mamual.
Here is how you determine if there is enough refrigerant in the system;

Mike Bradbury · 07-24-2009, 11:01 PM

Yes, sorry that is what I am looking for. How many # to re charge. The manual was very helpful, so if I am reading your post correctly the whole system only takes 3 pounds 4 oz to fill.

**WorkinLonghorn** · 07-24-2009, 11:17 PM

Yes,here is the actual article,with some other usefull info;

Mike Bradbury · 07-24-2009, 11:21 PM

Perfect, that I think exactly what I need thanks!

07-24-2009, 08:02 PM	#1
Mike Bradbury Registered User Join Date: Apr 2008 Location: San Diego California Posts: 1,316	R12 pressure? I searched the archives for the answer and most dealt with the conversion to 134a. My question is how much pressure is in the '69 truck R12 system? I have a friend in the AC business and he has R12 and the compatible replacement as well, he needed to know how much pressure was in the system in order for him to recharge it. All else works fine just low on charge, I would rather fix it for free rather than convert to 134a for now, I know it will probably be inevitable though. __________________ I'd rather attempt something great and fail.. than try something ordinary and succeed. Norman Vincent Peale Project: Barn Raising http://67-72chevytrucks.com/vboard/s...d.php?t=414961 Project: 30 Be Low https://67-72chevytrucks.com/vboard/...d.php?t=830583

07-24-2009, 09:47 PM	#2
chevroletrucks Registered User Join Date: Sep 2002 Location: Northwest,Indiana Posts: 128	Re: R12 pressure? I'm pretty sure your talking about static pressure, I dont know if you will find a spec. for that? At our shop we either read the gauges (compressor running) or did a complete evac to see how low it was. If memory serves decent typical running pressures for R-12 were 40psi (low side) 200psi (High side) This will vary depending on ambient temperature and humidity. Hope that helps some? __________________ 67' Chevy C10 Lwb small rear window 71' Gmc 1500 custom 4x4 72' Gmc Grande Sierra

07-24-2009, 09:52 PM	#3
El Jay Gone to greener pastures Join Date: May 2007 Location: Gateway to the Delta Posts: 7,354	Re: R12 pressure? The high side pressure will vary depending upon the ambient temperature. For example, at 80 degrees the high side pressure should be in the 150-170 psig range. At 100 degrees, it will be in the 210-230 psig range. No 2 systems will register exactly the same. The low pressure side should be between 15-30 psig, again depending upon ambient. These are just rough examples out of a 35+ year old Motor's Manual. I know that's not exactly what you were looking for, but I hope it helped you a bit. __________________ '69 Chevy 1/2 T LWB Stepper: Daily Beater '72 GMC 3/4 T Fleet: Another Daily Beater '72 Plymouth Gran Coupe: ? "Ah women. They make the highs higher and the lows more frequent." Friedrich Nietzsche "Never kick a fresh turd on a hot day." Harry S. Truman GUN CONTROL: Never having to say, "I missed you." Always fire two warning shots into your attacker's chest area before putting a bullet between his eyes. Paraphrased from Louis Awerbuck

07-24-2009, 10:46 PM	#4
Mike Bradbury Registered User Join Date: Apr 2008 Location: San Diego California Posts: 1,316	Re: R12 pressure? I know very little about the system, so I will tell him this info and hopefully it is what he needs. I think he was talking about with the compressor off, but not sure. __________________ I'd rather attempt something great and fail.. than try something ordinary and succeed. Norman Vincent Peale Project: Barn Raising http://67-72chevytrucks.com/vboard/s...d.php?t=414961 Project: 30 Be Low https://67-72chevytrucks.com/vboard/...d.php?t=830583

07-24-2009, 10:49 PM	#5
WorkinLonghorn Senior Member Join Date: Dec 2006 Location: Studio City, Calif. Posts: 2,861	Re: R12 pressure? Maybe he was asking what the R-12 "charge" is ,which is how many lbs. and onces it takes to charge an empty system. The charge is listed as 3 Lbs.,4 ozs. in the 1969 mamual. Here is how you determine if there is enough refrigerant in the system; Attached Images __________________ '69 GMC C2500 Custom Camper, 8 1/2' bed, New GM 350, NP 435 Close Ratio 4spd. Trans., 3.73 Dana-60 open.Camper and Trailer wiring, PS, PB, AC, tach , three gas tanks, 2nd owner, Work-Truck supreme. Best $300 I ever spent.

07-24-2009, 11:01 PM	#6
Mike Bradbury Registered User Join Date: Apr 2008 Location: San Diego California Posts: 1,316	Re: R12 pressure? Yes, sorry that is what I am looking for. How many # to re charge. The manual was very helpful, so if I am reading your post correctly the whole system only takes 3 pounds 4 oz to fill. __________________ I'd rather attempt something great and fail.. than try something ordinary and succeed. Norman Vincent Peale Project: Barn Raising http://67-72chevytrucks.com/vboard/s...d.php?t=414961 Project: 30 Be Low https://67-72chevytrucks.com/vboard/...d.php?t=830583

07-24-2009, 11:17 PM	#7
WorkinLonghorn Senior Member Join Date: Dec 2006 Location: Studio City, Calif. Posts: 2,861	Re: R12 pressure? Yes,here is the actual article,with some other usefull info; Attached Images __________________ '69 GMC C2500 Custom Camper, 8 1/2' bed, New GM 350, NP 435 Close Ratio 4spd. Trans., 3.73 Dana-60 open.Camper and Trailer wiring, PS, PB, AC, tach , three gas tanks, 2nd owner, Work-Truck supreme. Best $300 I ever spent.

07-24-2009, 11:21 PM	#8
Mike Bradbury Registered User Join Date: Apr 2008 Location: San Diego California Posts: 1,316	Re: R12 pressure? Perfect, that I think exactly what I need thanks! __________________ I'd rather attempt something great and fail.. than try something ordinary and succeed. Norman Vincent Peale Project: Barn Raising http://67-72chevytrucks.com/vboard/s...d.php?t=414961 Project: 30 Be Low https://67-72chevytrucks.com/vboard/...d.php?t=830583



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