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#1 |
Registered User
Join Date: Apr 2007
Location: pasadena,TEXAS
Posts: 880
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AC pressure question with r12
What should the pressures be with a correctly filled system of r12? I put in the correct amount according to the manual but it is only about 70* at the vents. the gauges show 26 on the low side and 265 on the high side at 2000 rpms. what are the correct pressures ? about the system new evap. condenser dryer & hoses. remanufactured compressor. just trying to get it right
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1971 Cheyenne SWB 402BB, 700R4, 3.73 posi, PS, PB, A/C, Tilt, Tach "Wanda" Don't argue with idiots, People watching may not be able to tell the difference... There's someone in my head........But it's not me...... cheap tricks thread great info here!! http://67-72chevytrucks.com/vboard/s...d.php?t=489394 |
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#2 | |
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Join Date: Dec 2015
Location: Pasadena, MD
Posts: 344
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Re: AC pressure question with r12
Quote:
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1972 K-20 Custom Camper 1971 K2500 Custom Camper (Sold) 2014 GMC 2500HD DMAX |
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#3 |
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Join Date: Apr 2007
Location: pasadena,TEXAS
Posts: 880
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Re: AC pressure question with r12
Pasadena texas is i'm sure like Pasadena Maryland about 20 feet above sea level. hum wonder why my low is lower than yours and my high is higher at this point. since I don't know a whole lot about ac's, is that normal???
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1971 Cheyenne SWB 402BB, 700R4, 3.73 posi, PS, PB, A/C, Tilt, Tach "Wanda" Don't argue with idiots, People watching may not be able to tell the difference... There's someone in my head........But it's not me...... cheap tricks thread great info here!! http://67-72chevytrucks.com/vboard/s...d.php?t=489394 |
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#4 |
Registered User
Join Date: Dec 2015
Location: Pasadena, MD
Posts: 344
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Re: AC pressure question with r12
Again, Im not an expert...lol, but I believe low readings on the low side would usually be a result of the orifice tube being dirty. Pretty sure that tube being restricted can cause higher readings on the high side too. Maybe replace the orifice tube and since you are opening the system anyway....replace the dryer and expansion valve. Vacuum it down and recharge it. That's what I did anyway.
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1972 K-20 Custom Camper 1971 K2500 Custom Camper (Sold) 2014 GMC 2500HD DMAX |
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#5 | |
Registered User
Join Date: Apr 2007
Location: pasadena,TEXAS
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Re: AC pressure question with r12
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1971 Cheyenne SWB 402BB, 700R4, 3.73 posi, PS, PB, A/C, Tilt, Tach "Wanda" Don't argue with idiots, People watching may not be able to tell the difference... There's someone in my head........But it's not me...... cheap tricks thread great info here!! http://67-72chevytrucks.com/vboard/s...d.php?t=489394 |
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#6 | |
Registered User
Join Date: Dec 2015
Location: Pasadena, MD
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Re: AC pressure question with r12
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1972 K-20 Custom Camper 1971 K2500 Custom Camper (Sold) 2014 GMC 2500HD DMAX |
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#7 |
Registered User
Join Date: Jun 2014
Location: Ingleside, IL
Posts: 56
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Re: AC pressure question with r12
When assembling the system was it purged with nitrogen and evacuated to at least 100 microns? If not then the non condensables would account for the high head pressures. Need this info before moving forward.
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#8 |
Registered User
Join Date: Jun 2016
Location: Chino Hills, CA
Posts: 2
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Re: AC pressure question with r12
Sounds like either air in the system or a restriction somewhere. Might be a combination of things but you would not expect to see 265 psi (160F) on the high side unless it was really hot outside or the condensing coil was not getting air flow. 26 psi # is 27 degrees on the evaporator coil, check out a R12 PT chart. With a 27 degree coil you should have cold air. The elevation has nothing to do with the pressure of a refrigeration system. Like SJLenz is getting to, the most important question, did you pull a vacuum before charging the system with refrigerant?
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#9 |
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Join Date: Dec 2015
Location: Pasadena, MD
Posts: 344
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Re: AC pressure question with r12
According to the GM service manual it does. The POA is where the low readings are taken i'm pretty certain.
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#10 |
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Location: Harrison, Arkansas
Posts: 9,815
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Re: AC pressure question with r12
Are you sure the heat/air diverter door is adjusted, or is closing? Is the valve in the heater hose working?
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other Larry Build thread, Arkansas K10 https://67-72chevytrucks.com/vboard/...=755797&page=5 The ability to speak several languages is an asset, but the ability to keep your mouth shut in any language is priceless. |
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#11 | |
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Join Date: Apr 2007
Location: pasadena,TEXAS
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Re: AC pressure question with r12
Quote:
It was pressured up with N2 and a vacuum was pulled but the on the first can which was oil the part that pierces the top of the can broke so we had to stop and it was a few days before I got the freon in, so that may be where I screwed up. The AC guy that refurbished and rebuild the poa called me and we talked for a while about it. I'm going to talk to some old ac guys at a shop near me. But a transmission problem came up this weekend that I need to address before I can drive it over there
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1971 Cheyenne SWB 402BB, 700R4, 3.73 posi, PS, PB, A/C, Tilt, Tach "Wanda" Don't argue with idiots, People watching may not be able to tell the difference... There's someone in my head........But it's not me...... cheap tricks thread great info here!! http://67-72chevytrucks.com/vboard/s...d.php?t=489394 |
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#12 | |
Registered User
Join Date: Dec 2015
Location: Pasadena, MD
Posts: 344
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Re: AC pressure question with r12
Quote:
I would let it sit in vacuum for at least 4hrs to verify everything is good. I let mine sit in vacuum over night. I did not charge mine with N because I did not have access to it, but you can if you like. Good luck!
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1972 K-20 Custom Camper 1971 K2500 Custom Camper (Sold) 2014 GMC 2500HD DMAX |
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#13 |
Registered User
Join Date: Mar 2001
Location: Paradise TX USA
Posts: 1,200
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Re: AC pressure question with r12
This system doesn't use an orifice tube. It has a Thermostatic expansion valve which has a small screen in the inlet that can get plugged up causing problems. If you haven't replaced it, that would be a good place to start.
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#14 |
Senior Member
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Location: Harrison, Arkansas
Posts: 9,815
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Re: AC pressure question with r12
I agree with pretty much everything that has been suggested, but don't forget, if that diverter door that changes from heater to air conditioning, is not letting air blow across the evaporator it will throw all readings off.
Have you checked temps at the back side of the POA valve, and below the expansion valve?
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other Larry Build thread, Arkansas K10 https://67-72chevytrucks.com/vboard/...=755797&page=5 The ability to speak several languages is an asset, but the ability to keep your mouth shut in any language is priceless. |
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#15 |
Registered User
Join Date: Mar 2001
Location: Paradise TX USA
Posts: 1,200
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Re: AC pressure question with r12
Yep, the blend air door has to be working properly, or it will never cool like it is supposed to. It has to block off the flow or air through the heater core and divert it through the evaporator core. Loosen the temperature control cable and move the door manually to make sure it is working right.
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#16 | |
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Join Date: Dec 2015
Location: Pasadena, MD
Posts: 344
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Re: AC pressure question with r12
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