73 Valiant R12 AC system pressures

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C2ndLTpigeon

C2ndLTpigeon

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I am still running R12 in my 73 Valiant with factory AC, I have a little bit less than 3 12oz cans of R12 in it now. Seems like it could get a little bit colder.

With my manifold gauges hooked up what pressures should I be aiming for? I still see some bubbles in the sight glass. I would rather go by pressure than the sight glass.
 
Needs a little more if it still has bubbles. I use 50/250 as a guideline but the sight glass will tell you when it gets full and the duct temp will tell you if it's working properly. Many things effect pressures. Many variables. Ambient temperature being a big one. Plugged condenser or bad air flow is another. I don't have a service manual to look up capacity. Are there any underhood stickers with system capacity marked on them? You're at 2.25#. Another 1/4 to half pound might be what you need.
 
How was it pulling down when you evacuated it? Did you check the compressor shaft seal?

I usually pressure test my systems with nitrogen. For the average guy to do that you'd have to invest in a nitrogen regulator and cylinder, commonly available at commercial HVAC suppliers such as R E Michel's and Aireco, etc.
Suction pressure should be in the 30-42 psi range, and anything under 30 psi could result in evaporator icing. Discharge pressure is a bit subjective, depends on load and outdoor ambient. The FSM has an excellent section in the back for checking load. To do it like a pro you need to know the humidity, aka wet bulb temp for old timers.
 
toolmanmike said:
I use 50/250 as a guideline b .
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Mike what are you talking about??? We are talking about R12 here. Discharge should not be anywhere near that high and low side should be "in the 20's"
 
Demonic said:
How was it pulling down when you evacuated it? Did you check the compressor shaft seal?

I usually pressure test my systems with nitrogen. For the average guy to do that you'd have to invest in a nitrogen regulator and cylinder, commonly available at commercial HVAC suppliers such as R E Michel's and Aireco, etc.
Suction pressure should be in the 30-42 psi range, and anything under 30 psi could result in evaporator icing. Discharge pressure is a bit subjective, depends on load and outdoor ambient. The FSM has an excellent section in the back for checking load. To do it like a pro you need to know the humidity, aka wet bulb temp for old timers.
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Im here in CA and if I were to check it in the morning like today its 77 degrees out at 8 AM with 30% humidity.

The system had no Freon when I bought the car 4 weeks ago, we pressurized it with Air and showed a good system with no restrictions. Then I used a Vac pump to suck the moisture and make sure the system had no leaks, it held Vac for over 2 hours.
 
toolmanmike said:
Needs a little more if it still has bubbles. I use 50/250 as a guideline but the sight glass will tell you when it gets full and the duct temp will tell you if it's working properly. Many things effect pressures. Many variables. Ambient temperature being a big one. Plugged condenser or bad air flow is another. I don't have a service manual to look up capacity. Are there any underhood stickers with system capacity marked on them? You're at 2.25#. Another 1/4 to half pound might be what you need.
Click to expand...

I believe the factory manual I have calls for 2 lbs 14oz for Valiants.
 
67Dart273 said:
Mike what are you talking about??? We are talking about R12 here. Discharge should not be anywhere near that high and low side should be "in the 20's"
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Probably from a temp chart like this.
ac temp chart.jpg
 
C2ndLTpigeon said:
I believe the factory manual I have calls for 2 lbs 14oz for Valiants.
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If that is the case you need 10 more oz. I would introduce another can until the sight glass clears up. Make sure your cooling fan/fan clutch is working properly. I often aim a box fan into the condenser to help it cool. Watch your duct temp. Depending on your outside temp and humidity today it should cool into the low 40's to mid 30's if is working properly.
 
Im getting a fluctuating low side. Here is video of the system running, sorry for the bad quality, I was trying to give it some throttle while recording. Temp outside is 85 with 21% humidity now.

 
C2ndLTpigeon said:
Im getting a fluctuating low side. Here is video of the system running, sorry for the bad quality, I was trying to give it some throttle while recording. Temp outside is 85 with 21% humidity now.

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Is it charged? does it cool? Is the compressor excessively noisy? You're good. Silicone dampened gauges aren't as steady as the liquid filled gauges. What is your ac duct temperature?
 
toolmanmike said:
Is it charged? does it cool? Is the compressor excessively noisy? You're good. Silicone dampened gauges aren't as steady as the liquid filled gauges. What is your ac duct temperature?
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Compressor is not noisy, inside AC duct was blowing 70 when it was 85 outside.
 
C2ndLTpigeon said:
Compressor is not noisy, inside AC duct was blowing 70 when it was 85 outside.
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What is the suction line temp returning to compressor? Could be a bit low on charge, something plugged, or evap cold and fan not high speed I like to at least get an estimate on supercooling which is given by low side pressure and low side temp. Are windows up? Some of those systems have that oddball suction pressure regulator but I don't think the little cars normally use it.
 
C2ndLTpigeon said:
Compressor is not noisy, inside AC duct was blowing 70 when it was 85 outside.
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Let's go back to basics before we go any further. Tell us the story. Is the car new to you? Did it cool before? Did you do any repairs?
 
C2ndLTpigeon said:
Im getting a fluctuating low side. Here is video of the system running, sorry for the bad quality, I was trying to give it some throttle while recording. Temp outside is 85 with 21% humidity now.

Click to expand...


The system is still low. See how fast the compressor is cycling? It needs more refrigerant.

...and as for the "50/250" rule, I've used that all my life charging R12. 134 takes more pressure on the high side. It usually ends up "somewhere" around 30/300. All dependent on ambient temperature and humidity and "all that". If it's a real hot and humid day, I've seen 134 pressure reach out and touch 375 "or so".
 
Low side showing the low pressure switch cutting power to the clutch. At a slightly higher than idle I would shoot for 30-35 on the low side and 200-250 on high side.
 
If it is the old RV-2 compressor, it should bring the duct temp to 34-40 with the windows up and fan on high. Make sure your moving enough air across the condenser. I use a fan.
 
The car is new to me as of April 13th, prev owner said the expansion valve was replaced which it has. To check for leaks I filled the system with air from my compressor, there are no leaks by sound and on the gauges. So I then Vacuumed the system for an hour and let it sit for 2 more and it held about 28 hg. Filled the system with about 3 12 oz cans of R12. I believe it is still a little low as the Factory manual calls for 2lbs 14oz Which would be 46oz. I have 1 12oz can left. My main question is what were normal pressures as I usually go off of that when filling my 134a systems. R12 is new to me as this is the only car I own that uses it still and I know it runs at different pressures than 134a. My main concern is I do not want to over pressurize the system.

The coldest duct temp inside the car I was able to get it at was 97 degrees outside temp and blowing 68 inside the car this was while driving and getting the speed up to 50+ MPH. The condenser is clean with no blockages.

The other thing in regards to the pressure surge, when the AC is on the Max AC setting the compressor always stays on and I never hear it click on and off. It will however click on and off it is on the AC setting. So that video I posted with the bouncing low side, the compressor clutch was engaged the whole time.
 
C2ndLTpigeon said:
So based on the info I provided, How are the pressures and should I add more R12?
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You know, there's some smart guys on here but with a/c it will tell you when it needs more. If the system is healthy and the duct temp is low, add a little more freon, let it stabilize and monitor the duct temp. Take it for a drive if need be with the thermometer in the duct. AC to me is a lot of common sense. If the temp goes up sitting at idle or at a stop sign, check the fan and condenser and radiator for restrictions. If the compressor is noisy, it needs oil or replacement. If a line is cold and all of a sudden warm (and a expansion valve isn't inline) there is a restriction. I have charged dozens of systems without any gauges and just a thermometer.
 
toolmanmike said:
You know, there's some smart guys on here but with a/c it will tell you when it needs more. If the system is healthy and the duct temp is low, add a little more freon, let it stabilize and monitor the duct temp. Take it for a drive if need be with the thermometer in the duct. AC to me is a lot of common sense. If the temp goes up sitting at idle or at a stop sign, check the fan and condenser and radiator for restrictions. If the compressor is noisy, it needs oil or replacement. If a line is cold and all of a sudden warm (and a expansion valve isn't inline) there is a restriction. I have charged dozens of systems without any gauges and just a thermometer.
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I think it will need a little more then, Seems to only be 20-25 degrees cooler than ambient temp. The line is cold and the other hot and the compressor is good with no noise. My main concern is the pressures with R12, I have learned they are lower than 134a, I mainly don't want to over pressurize the system. I will do as mentioned and pay attention to the duct temp and add freon and keep an eye on the sight glass.
 
If the compressor's cycling on and off quickly and the ambient temperature is above 80*, it needs more.
 
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