# Pressure temperature chart for refrigerants



## Samart (Apr 18, 2011)

Hi guys,

I have couple of questions.
1)The pressure values listed on this chart are suction pressure or discharge pressure?
2)Is the temperature listed is ambient temperature.

Thanks for your help!

Sam


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## yuri (Nov 29, 2008)

What chart? Click on Go Advanced and follow instructions to upload a jpeg etc.


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## Samart (Apr 18, 2011)

yuri said:


> What chart? Click on Go Advanced and follow instructions to upload a jpeg etc.


I got the chart but what to understand the following:
1)The pressure values listed on this chart are suction pressure or discharge pressure?
2)Is the temperature listed is ambient temperature.

Thanks for your help!

Sam


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## JJboy (Oct 12, 2010)

The temperature is related to the pressure. When the temperature changes the pressure increase or decrease.


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## Samart (Apr 18, 2011)

JJboy said:


> The temperature is related to the pressure. When the temperature changes the pressure increase or decrease.


Thanks for the reply. I understand that, but not sure if the pressure values listed on the pressure temperature chart are suction pressure values or discharge pressure.


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## Marty S. (Oct 31, 2009)

So long as there's a saturated mix of both liquid and gas present it covers everything. Look at your chart and tell me what the R22 temp shows with a suction pressure of 60. Now look at the chart and tell me what it is on a 180 psig liquid line. How about a R22 tank with vapor and liquid in it at a room temp of 70 degrees?


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## Samart (Apr 18, 2011)

Marty S. said:


> So long as there's a saturated mix of both liquid and gas present it covers everything. Look at your chart and tell me what the R22 temp shows with a suction pressure of 60. Now look at the chart and tell me what it is on a 180 psig liquid line. How about a R22 tank with vapor and liquid in it at a room temp of 70 degrees?


R22 shows 34 F at 60psi and 93F at 180psi. At 70F the pressur is showing around 120psi. 
Please put some more light.
Thanks


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## Samart (Apr 18, 2011)

Marty S. said:


> So long as there's a saturated mix of both liquid and gas present it covers everything. Look at your chart and tell me what the R22 temp shows with a suction pressure of 60. Now look at the chart and tell me what it is on a 180 psig liquid line. How about a R22 tank with vapor and liquid in it at a room temp of 70 degrees?


I will wait for your response.
Thanks a lot


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## JJboy (Oct 12, 2010)

1)The pressure values listed on this chart are suction pressure or discharge pressure?


Compressor does the change low pressure to high pressure. So the temp changes low to high temp..... What is your question?


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## Marty S. (Oct 31, 2009)

That's all there is to it,a relationship between pressure and temp for a given refrigerant. You have a system running 60/180. The suction line measures 50 degrees so how much is the refrigerant super heated ? The liquid line measures 80 which means you have what for subcool?


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## Samart (Apr 18, 2011)

JJboy said:


> 1)The pressure values listed on this chart are suction pressure or discharge pressure?
> 
> Compressor does the change low pressure to high pressure. So the temp changes low to high temp..... What is your question?


I mean when to compare the pressure values on the PT chart with the actual suction pressure reading on the ac and when to compare with the actual discharge pressure reading


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## Samart (Apr 18, 2011)

Marty S. said:


> That's all there is to it,a relationship between pressure and temp for a given refrigerant. You have a system running 60/180. The suction line measures 50 degrees so how much is the refrigerant super heated ? The liquid line measures 80 which means you have what for subcool?


I mean when to compare the pressure values on the PT chart with the actual suction pressure reading on the air conditioner and when to compare with the actual discharge pressure reading


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## JJboy (Oct 12, 2010)

The difference between the temps that you are ​​measuring with a thermometer and the values ​​of PT chart are due to the SH and SC


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## Samart (Apr 18, 2011)

JJboy said:


> The difference between the temps that you are ​​measuring with a thermometer and the values ​​of PT chart are due to the SH and SC


Does the temperatures on the PT chart indicate the ambient temperature or the pipe temperature? 
Thanks for your help


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## JJboy (Oct 12, 2010)

PT chart indicate the temp of the environment where is the refrigerant. The pipe temperature it's the measured temp


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## Samart (Apr 18, 2011)

JJboy said:


> PT chart indicate the temp of the environment where is the refrigerant. The pipe temperature it's the measured temp


I think technicians check the suction pressure on the system and compare it with the pressure on the PT chart to see if their actual reading on the system is off and they do the same thing with the discharge pressure. Am I right sir?
I mean for example at 72F ambient/environment temperature the PT chart for R22 shows the pressure as 125 but when the tech actual reading is way below 125, this means that the suction pressure in the system is low. May be there is some restriction in the system. Please correct me if I am wrong. Again, thanks for all ur help.


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## JJboy (Oct 12, 2010)

Yes, with these values ​​we can determine if the unit is undercharge, overcharge, with restrictions, contaminated. etc


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## beenthere (Oct 11, 2008)

The pressure and temps on the PT charts are saturation pressures and temps. They are not suction or discharge temps or pressure. this is the pressure the refrigerant will exert at X degrees provided that both liquid and vapor are in the container(as said earlier).

The chart is used to determine the amount of subcool or superheat the system is operating at. Not what it should be operating at. 

Take a new cylinder of R22, at 32°F it will have 58PSIG in it. At 83°F the same tank with the same amount of refrigerant in it will have a PSIG of 180. The reason is that it is a saturated refrigerant. Meaning that the refrigerant is existing in the cylinder as both liquid and vapor. As the refrigerant warmed up, more of the liquid boiled off to vapor, and the vapor takes up more space then the liquid did, so the pressure increased. But the total mass in the cylinder remained the same.

You may want to read up on "saturation".


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## Samart (Apr 18, 2011)

beenthere said:


> The pressure and temps on the PT charts are saturation pressures and temps. They are not suction or discharge temps or pressure. this is the pressure the refrigerant will exert at X degrees provided that both liquid and vapor are in the container(as said earlier).
> 
> The chart is used to determine the amount of subcool or superheat the system is operating at. Not what it should be operating at.
> 
> ...


Thanks beenthere for the detailed explanation. One question: when does the ambient temperature used on the PT chart? I mean for an ac system in a room.


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## Hubcap626 (Feb 12, 2011)

Samart said:


> Thanks beenthere for the detailed explanation. One question: when does the ambient temperature used on the PT chart? I mean for an ac system in a room.


Ambient temperature has nothing to do with a PT chart. It has to do with the refrigeration pressure and temperature. 

The only real reason I use a PT chart for is when my gauges are on a circuit and it's a refrigerant that my gauges don't give me a temperature for. Say 407c. I get my pressure because that will always be the same on any Gage. I then go to my PT chart and find the corresponding temperature for that pressure under that refrigerant.

You may be talking about a psychometric chart? Where you have dry bulb, wet bulb, enthalpy and other items on the chart.


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## HVACDave (Oct 16, 2007)

When we put guages on your system and check the pressures we are seeing what the operating characteristics are in your system. 

When my suction guage says 60 Psi on an r-22 system in an outdoor ambient of 75F it is telling me that the refrigerant in the evaporator is boiling off at about 34 F. This tells me that you are getting pretty close to max cooling out of the coil. As the load on the evaporator rises the suction pressure will also rise. Airflow through the evaporator is key for this to work properly. 

The discharge pressure tells me how hard the compressor is working. Typically the discharge should be approximately 30F above ambient temps on the chart, so if it were 75F outside I would add 30 F to make it 105 F and the corresponding pressure would be about 210 psi. of course the condition of the condenser coil (clean or dirty) would impact this pressure significantly. 

I would also use these pressures and temps to calculate subcooling and superheat values to check the charge in your system as well as things like compression ratio of the compressor, which would give an indication of it's efficiency etc. Getting too deep. Hope this is what you were looking for.


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## beenthere (Oct 11, 2008)

As the others said, ambient temp and the PT chart don't really get used together with a refrigeration system/circuit. The only time it is really used with ambient temp, is when your checking the calibration of your gauges.

Perhaps if you explain what type of charging problems concerns you have, we can better tell you how to check charge of a system.


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