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What are correct A/C pressures for a charged system?

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01eddie

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O.K., Here is where I am at the moment....

A/C didn't work, checked to see that compressor would still click on- it did. Bought a can of "EZ Chill" 134a for $18 at Wally world. came in a tall can with lubricant added and leak sealer. also had hose with it that had built-in pressure guage.

I hooked it up to the low pressure side, pressure read zero. I started the truck, turned on the a/c to max and started spraying the can. pressure started building soon, and compressor clicked on. the off. then on. then off......etc.

I added about 3/4 of the 18 oz can. the pressure while running and the a/c on is 47 PSI then the compressor clicks on, slowly drains the pressure down to about 19lbs, at which point the compressor stops, the pressure builds back to 47 PSI, repeat. I thought I must need to add more, and I probably do, but if I turn the truck off the pressure read 125 PSI.

I wanted to make sure that this is O.K.. I havent seen what the pressure is supposed to be if the truck isn't running, but I thought I better ask since I know that the system is sensitive to being over filled.

What should the pressure be while the Compressor is running? how high is the pressure of a correctly charged system when the truck isn't running? could any one check theirs?

thanks again for all your help- I should be driving back in the cool soon!

Brian
 



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Blee1099

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Whats the ambient temperature outside?

At around 90, your low pressure should be 25-30 psi and the high side should be 200-220 psi.
 






manaen

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These are all low side pressure readings with the AC running on Max AC

Ambient Temp in F--------Low Side Reading
65 ---------------------- 25-35 psi
70 ---------------------- 35-40 psi
80 ---------------------- 40-50 psi
90 ---------------------- 45-55 psi
95 ---------------------- 50-55 psi
100 ---------------------- 50-55 psi
110 ---------------------- 50-55 psi



that covers the low side readings
 






Blee1099

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Please go out and purchase the right tools.. Those single port ez-fill systems are junk.. Go out get a set of manifold guages and a tap for the cans. Don't forget about the oil for the lube. Charging using one of those ez-fills often leads to overcharging the system.
 






01eddie

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Thanks for the responses, I don't think that I am fully charged yet.

Unfortunately, the single port cans are all that fits my budget at the moment. I would love to go down and drop 100-200 to get it done correctly, but this is where I am at the moment.

can anyone with functioning A/C tell me what there low pressure side reads when the vehicle is not running?
 






manaen

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It doesn't matter what it reads not running, the system should always be tested and filled with the AC on max. Your pump is shutting off because you don't have enough refrigerant and the low side PSI sensor is dropping below 20psi which turns off your pump. It is always good practice to check the high side pressure as well just to make sure there are no blockages. You should be able to borrow a high side gauge for free from autozone or whatever parts place you have local. You can use the easy fill can you have, just make sure your pressures are good with the system running.
 






01eddie

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I added the remaining quarter of the 18oz. can and then added a full 12 oz can as well. The compressor now stays on and the pressure with the compressor running is about 39 PSI with an outside air temp of 76 degrees F. The Air now works inside the truck and it definately cooler inside with Air set on Max and the climate controller set at 65 Degrees F.

Thanks again to everyone for all your help. It was an easy fix and only cost about $30. It may not have quite the cooling capacity that it would have if the system have been exausted first, but the air now works and that is WONDERFUL!!

And thanks to Manean for that Pressure/ambient temp table! That thing should be a sticky- I'm sure a lot of people have the same question!
 






Cobraguy

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These are all low side pressure readings with the AC running on Max AC

Ambient Temp in F--------Low Side Reading
65 ---------------------- 25-35 psi
70 ---------------------- 35-40 psi
80 ---------------------- 40-50 psi
90 ---------------------- 45-55 psi
95 ---------------------- 50-55 psi
100 ---------------------- 50-55 psi
110 ---------------------- 50-55 psi



that covers the low side readings

If I can't get an R134A low side into the 30's at 95 psi, I would quit. I don't know where that chart came from, but it's horrible. It appears to be one of those manufacturer "cop out" charts. You know...they say, "well, your pressures are where the factory says they should be, so there's nothing we can do about your crappy a/c performance."
 






manaen

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If I can't get an R134A low side into the 30's at 95 psi
I assume you mean around 30psi at 95degs?
And you mention nothing about the high pressure readings, which says little about system performance.

I don't know where that chart came from, but it's horrible
I will admit the chart is rather old, but it is taken from a ford tech manual. If you have an updated chart please take the time to post it and explain why. It does no good say things like that and then not explain you conclusions. If you have useful information to share, then do so...
 






Cobraguy

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I don't care where that chart comes from...I stand by my comment about it. It's horrible and any a/c tech that lives by that shouldn't be in the business. C'mon...think about what that is telling you there. Two weeks ago, I serviced a Lincoln LS, a Nissan Frontier, and two Explorers in my garage. Door was open and it was appx105 to 110 degrees outside. All vehicles had outside air thermometers on them and they all read between 95 and 100 in my garage. Every one had low side pressures under 40 psi. Every single one. Duct temps were all in the mid to low 40's. That is with nothing more than a fan blowing in front of the radiator. Going down the highway, they will go lower.

High side was never brought up. so I didn't mention it. But at 95 to 105 degrees, you can see high side pressures way up there...depending on the amount of airflow across the condenser. 225 to 250 psi are not uncommon with the car in a service bay.

I'm not bitching at you in the least. Far from it. That chart is a cop out. I can promise you that you would not live with an a/c system with some of those readings.
 






omgyouresexy

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I hooked up my manifold set yesterday and recharged with one can. While running, the low side was at 35, high at 230... it was approx 85-90 outside.

I wanted to make sure it wasn't overcharged, or that I didn't need to add more. I think I have a slow leak, but I'm not too sure. I think the pressures while off we're at 110... and I assume I could check the off pressure again a month later and see if it's drop to look for a leak. Sound like an appropriate way to check for a leak?
 






myf16

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My high side only goes to about 145 psi. It doesn't blow very cold and the compressor cycles on and off every 20 seconds or so.

This is a 1996 with R134a. Should I just add a 12 oz can of R134a and measure it again?
 






myf16

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One can brought me to 36 psi and 225 psi high. It's cold and the compressor stays on at idle. I'm declaring success!
 






mike1955geneva

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I assume you mean around 30psi at 95degs?
And you mention nothing about the high pressure readings, which says little about system performance.


I will admit the chart is rather old, but it is taken from a ford tech manual. If you have an updated chart please take the time to post it and explain why. It does no good say things like that and then not explain you conclusions. If you have useful information to share, then do so...

Sounds like R-12 pressures to me. Auto Mechanic since 1973, don't have a current chart but will get one by weekends end and post. Good luck.
 






mike1955geneva

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O.K., Here is where I am at the moment....

A/C didn't work, checked to see that compressor would still click on- it did. Bought a can of "EZ Chill" 134a for $18 at Wally world. came in a tall can with lubricant added and leak sealer. also had hose with it that had built-in pressure guage.

I hooked it up to the low pressure side, pressure read zero. I started the truck, turned on the a/c to max and started spraying the can. pressure started building soon, and compressor clicked on. the off. then on. then off......etc.

I added about 3/4 of the 18 oz can. the pressure while running and the a/c on is 47 PSI then the compressor clicks on, slowly drains the pressure down to about 19lbs, at which point the compressor stops, the pressure builds back to 47 PSI, repeat. I thought I must need to add more, and I probably do, but if I turn the truck off the pressure read 125 PSI.

I wanted to make sure that this is O.K.. I havent seen what the pressure is supposed to be if the truck isn't running, but I thought I better ask since I know that the system is sensitive to being over filled.

What should the pressure be while the Compressor is running? how high is the pressure of a correctly charged system when the truck isn't running? could any one check theirs?

thanks again for all your help- I should be driving back in the cool soon!

Brian

The pressures will equalize when the vehicle is not running. If you were on zero when you started you have a leak. Look for an area that has oil around it [ there will be dirt or dust in the area where the oil is at. Oil means leak ] This is a tell tell sign. If its a small leak the leak sealant may fix it. About a 50/50 chance. I don't have a current R-134A chart, but I will have one by weekends end and post it. Good luck, will post back later on this weekend.
 






garye

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Sounds like R-12 pressures to me. Auto Mechanic since 1973, don't have a current chart but will get one by weekends end and post. Good luck.

So can you post a current pressure chart?
Thanks
 






Mesozoic

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We just measured high side pressures at over 320 psi. My buddy thinks the A/C system is overcharged a bit. Sure enough, he removed a few ounces of refrigerant and it's blowing cold again. Anyone have a better explanation regarding high side pressures? Granted, it was around 117 degrees F when the system exhibited issues.
 






ice_cold1011

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Thanks for the responses, I don't think that I am fully charged yet.

Unfortunately, the single port cans are all that fits my budget at the moment. I would love to go down and drop 100-200 to get it done correctly, but this is where I am at the moment.

can anyone with functioning A/C tell me what there low pressure side reads when the vehicle is not running?
You probably don't need to know this any longer but when the vehicle is off the high and low side equalize, so yes it is normal.
 






James Thompson 7

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I added the remaining quarter of the 18oz. can and then added a full 12 oz can as well. The compressor now stays on and the pressure with the compressor running is about 39 PSI with an outside air temp of 76 degrees F. The Air now works inside the truck and it definately cooler inside with Air set on Max and the climate controller set at 65 Degrees F.

Thanks again to everyone for all your help. It was an easy fix and only cost about $30. It may not have quite the cooling capacity that it would have if the system have been exausted first, but the air now works and that is WONDERFUL!!

And thanks to Manean for that Pressure/ambient temp table! That thing should be a sticky- I'm sure a lot of people have the same question!
Since you added leak detector, get a UV pen light and look at all the connections in a dark space with motor on for a few to pump up pressures, then off to examine it for the leak glow. Glad you got it working!
 



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James Thompson 7

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Here is a pressure list I found for R138a
R-134a TEMPERATURE PRESSURE CHART
Ambient
Temperature °F / °C
(Temperatura Ambiental) Low-Pressure Gauge High-Pressure Gauge
65°F (18°C) 25-35 psi / 172-241 kPa 135-155 psi / 931-1069 kPa
70°F (21°C) 35-40 psi / 241-276 kPa 145-160 psi / 1000-1103 kPa
75°F (24°C) 35-40 psi / 241-310 kPa 150-170 psi / 1034-1172 kPa
80°F (27°C) 40-50 psi / 276-345 kPa 175-210 psi / 1207-1448 kPa
85°F (29°C) 45-55 psi / 310-379 kPa 225-250 psi / 1551-1724 kPa
90°F (32°C) 45-55 psi / 310-379 kPa 250-270 psi / 1724-1862 kPa
95°F (35°C) 50-55 psi / 345-379 kPa 275-300 psi / 1896-2068 kPa
100°F (38°C) 50-55 psi / 345-379 kPa 315-325 psi / 2172-2241 kPa
105°F (41°C) 50-55 psi / 345-379 kPa 330-335 psi / 2275-2310 kPa
110°F (43°C) 50-55 psi / 345-379 kPa 340-345 psi / 2344-2379 kPa
Ambient temp is the outside atmospheric temperature.
INTERPRETING PRESSURE READINGS
Low-Pressure Gauge High-Pressure
Gauge Action Required
IN RANGE IN RANGE A/C is working properly.
LOW LOW Add Refrigerant.
LOW HIGH Need service, possible blockage of the
expansion valve or orifice tube.
HIGH LOW Needs service, possibly faulty compressor.
HIGH HIGH System is overcharged. Slowly remove
refrigerant. Venting is illegal in USA.
 






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