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Photograph of a
commercial air conditioning compressor charging gauge set (C) InspectAPedia.com Air Conditioner Compressor & Refrigerant Pressure Readings
HVAC refrigerant pressures, quantities, boiling points, chemical formulas, Global Warming Impact GWP & ODP data

Refrigerant charge quantity for air conditioners & heat pumps:

This air conditioning repair article series discusses the the diagnosis and correction of abnormal air conditioner refrigerant line pressures as a means for evaluating the condition of the air conditioner compressor motor, which in turn, is a step in how we evaluate and correct lost or reduced air conditioner cooling capacity.

We explain how overcharging or undercharging of refrigerant in an air conditioner or heat pump is detected and we list the effects of overcharged or undercharged refrigerant. We discuss how to diagnose refrigerant pressure problems; how to determine the proper refrigerant charge quantity.

Definitions of Heating Ventilation Air Conditioning & Refrigeration (HVACR) "high side" & "low side" pressures; typical refrigerant pressures; effects of overcharged or under-charged refrigerant are found here as well.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

What are the Typical Air Conditioner or Heat Pump System Pressures During Normal Operation

Photograph of a
commercial air conditioning compressor charging chartMeasuring the refrigerant pressure in air conditioning, heat pump or other refrigerant systems can diagnose a range of operating problems including a refrigerant leak, over charging or under charging.

Refrigerant pressure readings measured at the air conditioning compressor/condenser unit and which are found to be too low on the high pressure side (compressor output) or on the low pressure side (compressor input or suction line) can indicate a problem with the compressor's ability to develop normal operating pressure ranges and thus will affect the cooling capacity of the air conditioning system.

Abnormally high compressor output pressures are possible but less likely.

Refrigerant Pressures & Pressure Diagnosis

Refrigerant Pressure & Leak Correction

If you already know your refrigerant pressures are wrong or that you have a refrigerant leak, please see

Overview of Refrigerant Types - past and current

The types of refrigerants can be a confusing soup of acronyms. Here's a summary of the different types of refrigerants:

In sum there were at least two classes of damage:

Holes in the ozone layer:

Chlorine-containing refrigerants that contributed to the ozone hole (consider getting skin cancer in Australia). These include CFCs and HCFCs.

Greenhouse gases:

Greenhouse gas formation that contributes to global warming. These include HCFCs and HFCs.

Environmental Alternatives

The EU has proposed more climate-friendly alternatives to HFCs. The article below provides a more-extensive list of alternatives to HFC type refrigerants.

In choosing refrigerants that reduce or eliminate the contribution of those products to global warming, alternatives include:

More about environmental concerns updates at

REFRIGERANT TYPE & ENVIRONMENTAL CONCERNS UPDATE

Comparison Table of Refrigerant Gas Properties

Comparison of Refrigerant Gas Properties

Refrigerant Gas Properties Refrigerant
Type
14
Replaces
Substitutes20
Replaced
By20
GWP1 ODP1

Com-
bustibile
1

Pressure Charts & Details

R11 Trichlorofluoromethane
CFC-11 = Freon-11 = R-11.
Banned-1996 Montreal Protocol
CFC     4000 1.0 Y Basis for ODP comparisons
R12 Dichlorodifluoromethane
Freon
No remaining life
Banned-1996 Montreal Protocol
CFC
HFC
  R124
R134a
R401a
R401b
2400 1.0 N n/a
R12 B1   CFC   R124, R142b     N  
R13 B1 Bromotrifluoromethane
Halon 1301 or BTM CBrF3
CFC
Halon
  R410A,
ISCEON®
MO89
R402B?
  10 N  
R22 Chlorodifluoromethane
No remaining life
Do not go to R-410A
HFC
HCFC
R404A R407c ? 1700 0.05 Y R22 REFRIGERANT PRESSURES
R22 pressure chart, high & low side
R23 Additions banned 1 Jan 2020
Reclaimed use permitted
to end of 2029
HFC R13, R503
Halon 131
  18,400 0 N  
R32 Difluoromethane, CH2F2
Use in new equipment
HFC R134A ?
R410A ?
      N ? R32 REFRIGERANT PRESSURES
Eco 32 Blend: Propane R290
+ Ethane R170
reduced-GWP

HC

R32, R410a   ? ? Y Eco-32 REFRIGERANT PRESSURES [PDF] 17
R32 Difluoromethane
R 410A replacement in
new equipment
Not to be used as a retrofit
HFC R410A 650 77119 0 Y R32 REFRIGERANT PRESSURES
R113

Trichlorotrifluoroethane
Banned-1996 Montreal Protocol

CFC     4800 0.8    
R114 Dichlorotetrafluoroethane
Banned-1996 Montreal Protocol
CFC   R124, R142b 3.9 1.0    
R123 Dichlorotrifluoroethane HCFC R11   0.02 0.02    
R1234YF Automotive AC
2,3,3,3-Tetrafluoropropene
HFO R134A   4   Y R1234YF PRESSURE CHART [PDF] 10
R1234ZW [citation needed]              
R124 Chlorotetrafluoroethane HCFC R12, R114   620 002    
R125 Pentafluoroethane       3400 0    
R134A

Tetrafluoroethane
Domestic HVAC, "Freon"
CFC Substitute
Short remaining life
Banned as of 2024

HFC R12
1234yf
R-152a
R-744
1300-
1430
0 N R134 REFRIGERANT PRESSURE CHART
R143A Trifluoroethane       4300 0    
R152A Difluoroethane       120 0 Y  
R245A Pentafluoropropane       ? 0 N Flammable under pressure
R290 Pure HC Propane, CARE® 40 HC

R12, R22,
R134A

R502 ?

  3 ? Y R290 PRESSURE CHART [PDF] 3
R401A Blend
53% R-22, 34% R-124,
13% R-152a
HCFC R12, R500?   1100 0.037 N  
R401B Blend
61% R-22, 28% R-124,
11% R-152a
HCFC     1200 0.04 N  
R402A / HP80 Blend of R-22 & R-125 w/
hydrocarbon R-290 (propane)
38% R-22, 60% R-125,
2% R-290
HCFC R502   2600 0.02 N R402A PRESSURE CHART [PDF] 13
R402B Blend of R-22 and R-218 w/
R-290 (propane)
HCFC R502
R-13B1?
      N  
R403B Blend of R-22 and R-218 w/
R-290 (propane)
HCFC R502       N  
R404A Blend, replaces R502 & R22
Short remaining life2
44% R-125, 52% R-143a,
R-134a
HFC R502, R22   3300
3922 ?
0 N R404A PRESSURE CHART [PDF] 4
Flammable under pressure
R407A Blend
20% R-32, 40% R-125,
40% R-134a
HFC R22   2000 0 N  
R407C Blend
23% R-32, 25% R-125,
52% R-134a
HFC R22   1600 0 N  
R407H Mixture of R32, R125, R134A,
not ozone resistant
HFC

R22, R-404A?,
R507

  1490
1495
- N

R407H PRESSURE CHART [PDF] 5 16

R408A / FX10 Blend, Forane® HCFC R502   3152 0.024 N R408A PRESSURE CHART [PDF] 13
R409A Blend of R-22, R-142b HCFC R12       N  
R410A

Domestic HVAC
Short remaining life
50:50 blend R32 + R125
Banned as of 2024

  R-22 R-32
Eco-32
2088   N R410A REFRIGERANT PRESSURE CHART
R414B Blend of R-22, R-124, R-142b
w/hydrocarbon R-600a
(isobutane)
HCFC

R12
Automotive

      N  
R448A Blend
R32, R125, R134A,
R1234YF, R1234ZW
HFC
HFO
R404A or R507   1273   N R448A / N40 PRESSURE CHART [PDF] 6
R449A Blend HFC
HFO
R404A   1282   N R449A PRESSURE CHART [PDF] 7
R452A Blend HFC
HFO
R404A, R507   1945   N R452A PRESSURE CHART [PDF] 8
R452B Blend
blend R32 + R125+ R1234yf?
HFC
HFO
R410A       Y  
R454B Blend HFO R410A       Y  
R500 Blend
R-12 / R-152a
Banned-1996 Montreal Protocol
CFC R12       N  
R502

Freon
(Chloropentafluoroethane)
Blend
48.8% R-22, 51.2% R-115
Banned-1996 Montreal Protocol

CFC R-22 / R115 R404A 4.1 0.283 N R502 PRESSURE CHART [PDF] 12
Becomes flammable under pressure
R507 Blend
50%-50% R-125 & R-143A - or
45% R-125, 55% R-143
HFC R22, R502   3300 0 N R507 PRESSURE CHART [PDF] 11
Becomes flammable under pressure
R600A Iso-butane   R12, R134   3   Y R600A PRESSURE CHART [PDF] 9
R717 Ammonia - NH3
Among oldest refrigerants

  R134A-?
R32-?
0 0 Y Flammable at high temp.
R718 Water - H20         0 N  
R729 Air         0 N  
R744 Carbon Dioxide - CO2
GWP REFERENCE GAS
      1 0 N  

Notes to the table above

  1. GWP = Global Warming Potential, relative contribution to global warming by contributing to greenhouse gases that trap heat in the earth's atmosphere. CO2 (Carbon dioxide) has a GWP of 1.0.

    By 2025, high Global Warming Potential (GWP) refrigerants with a GWP of over 750, will be banned together along with HVACR equipment that uses that gas. Note that GWP ratings are controversial.

    ODP = Ozone Depletion Potential - relative damage to the earth's ozone layer.

    ODP is defined as the total amount of ozone destroyed by that substance compared with the amount of ozone that would be destroyed by the same mass of CFC-11 = Freon-11 = R-11.

    Combustible or flammable: refrigerants are rated as
    1 - not flammable,
    2L - very low flammability,
    2 - low flammability,
    3 - high flammability

    - Source:
    ASHRAE: ASHRAE Standard 34 describes a shorthand way of naming refrigerants and assigns safety classifications based on toxicity and flammability data
    ASHRAE Standard 15 establishes procedures for operating equipment and systems when using those refrigerants.
  2. R404A, commercial use banned after 2020 is replaced by R448A, R449A, R452A, R407H.
  3. R290 PT Chart, A-Gas, Units 7 & 8 Gordano Court Serbert Close Portishead, Bristol BS20 7FS UK, +44 1275 376600 Offices world wide, Website: www.agas.com, retrieved 2020/02/10 original source: https://www.agas.com/media/2422/r290-propane-pt-chart.pdf

    Linde, R290 REFRIGERANT GRADE PROPANE [PDF] Linde AG Linde Gases Division, Seitnerstrasse 70, 82049 Pullach, Germany Phone +49.89.7446-0, Fax +49.89.7446-1230, www.linde-gas.com/refrigerants, refrigerants@lindegas.com retrieved 2021/12/22 original source: http://hydrocarbons21.com/files/refrigeration_R290.pdf
    Excerpt:

    R290 is the common name for high purity propane (C3H8) suitable for use in the refrigeration and air conditioning industry. It is also known as CARE® 40.
  4. R490 PT Chart, A-Gas, op. cit. retrieved 2020/02/10 original source: https://www.agas.com/media/2405/r404a-pt-chart.pdf
  5. R407 Data, Daikin Chemical Europe GmbH Am Wehrhahn 50 40211 Düsseldorf, Germany Phone: +49 211-179225-0 Fax: +49 211-179225-39 daikinchem.de, retrieved 2020/02/10 original source: https://www.daikinchem.de/sites/default/files/pdf/Refrigerants/Daikin_R407H_Handling_Brochure_EN.pdf

    R407H: zeotropic mixture of 32.5 weight% R32, 15 % R125, and 52.5% R134a. It is a drop-In refrigerant for R404A / R507 and a retrofit refrigerant for R22.
  6. R448A Data, (N40) Pressure & Temperature, FSW op. cit. retrieved 2020/02/10 original source: https://www.fsw.uk.com/sites/www.fsw.uk.com/files/r448a-n40-pt-chart.pdf

    Alternative Chart: R448A Data Honeywell's Solstice® N40 = R448A [PDF] Honeywell Advanced Materials 115 Tabor Road Morris Plains, NJ 07950 honeywell-refrigerants.com retrieved 2020/02/10 original source: https://www.fluorineproducts-honeywell.com/refrigerants/wp-content/uploads/2018/02/SPM-FLP-00643-PT-Chart-Solstice-N40_3x5_LR.pdf
  7. R449A / XP40 Data, FSW Cannock Delta House,Fairway, Bridgtown, Cannock, Staffordshire, WS11 0DJ Email Sales@fsw.uk.com Tel: 01543 437 010 retrieved 2020/02/10 original source: https://www.fsw.uk.com/sites/www.fsw.uk.com/files/r449a-xp40-pt-chart.pdf
  8. R452 Data, FSW, Op. Cit., retrieved 2020/02/10 original source: https://www.fsw.uk.com/sites/www.fsw.uk.com/files/r452a-xp44-pt-chart_0.pdf
  9. R600A Data, Iso-Butane, A-Gas, op. cit. retrieved 2020/02/10 original source: https://www.agas.com/media/2423/r600a-iso-butane-pt-chart.pdf
  10. R600A Data, Iso-Butane, A-Gas, op. cit. retrieved 2020/02/10 original source: https://www.agas.com/media/6742/r1234yf-pt-chart-2.pdf
  11. R507 Data, Agas, Op. Cit., https://www.agas.com/media/2421/r507-pt-chart.pdf
  12. R502 Datra, R502 is replaced by R402A / R-408A, retrieved 2020/02/10 original source: http://www.pchetz.com/_Uploads/dbsAttachedFiles/R502PressureEnthalpy.pdf
  13. R402A Data, REFRIGERANT CHANGEOVER GUIDELINES R-502 TO R-402A/R-408A [PDF] (2005) Copeland / Emerson Climate Technologies, 1675 W. Campbell Road Sidney, OH 45365-0669 (937) 498-3011 copeland-corp.com

    Excerpts: Copeland does not advocate the wholesale changeover of CFC refrigerants to HCFCs or HFCs. If a system is not leaking refrigerant to the atmosphere, and is operating properly, there is no technical reason to replace the CFC refrigerant.

    In fact, changing the refrigerant may void the U.L. listing of the unit. However, once the decision has been made to make the change from R-502 to the interim R-402A or R-408A, the following guidelines are recommended.

    R-402A/R-408A should be used only in systems that currently use R-502. It should not be mixed with R-502 or any other refrigerant nor should it be used to replace CFC-12 or HCFC-22
  14. R408A Data, see #13 above.
  15. Daikin, R407H PROPERTIES, USE & HANDLING [PDF] Daikin Chemical Europe GmbH Am Wehrhahn 50 40211 Düsseldorf, Germany Phone: +49 211-179225-0 Fax: +49 211-179225-39 daikinchem.de
    Excerpt:
    R407H can be used as a Drop-In refrigerant in R404A / R507 systems. A Drop-In is the easiest way to convert a refrigeration system to another refrigerant. It is linked with minor changes and it usually uses the same oil type.
  16. Eco Freeze, E.F. International bvba Boombekelaan 11E B-2660 Hoboken (Antwerp) Belgium + 32 498 648 933 – Arya Mohadjerin arya@eco-freeze.com source of our Eco-32 pressure chart given in the table above, retrieved 2021/12/22 original source: https://eco-freeze.com/resources/#32chart
  17. Engineering Toolbox, "Refrigerants - Environmental Properties, Refrigerants - Ozone Depletion (ODP) and Global Warming Potential (GWP)", retrieved 2021/12/22 original source: https://www.engineeringtoolbox.com/Refrigerants-Environment-Properties-d_1220.html
    This article provided data for some of the gas properties entered in the table above.
  18. The GWP of R32 was increased from 675 to 771 in August, 2021 by the Intergovernmental Panel on Climate Change (IPCC), sixth assessment report “Climate Change 2021 – The Physical Science Basis.”
  19. US EPA UNACCEPTABLE SUBSTITUTE REFRIGERANTS [PDF] U.S. EPA, retrieved 2021/12/22 original source: https://www.epa.gov/snap/unacceptable-substitute-refrigerants

Comparison of Ambient Pressure/Temperature for Refrigerants

Comparison of Refrigerant Pressures at 30°C / 86°F Ambient Temperature

Refrigerant Gas Gauge Pressure - BAR Gauge Pressure - PSIG

Pressure Charts & Details

R22 10.9 158.2 R22 REFRIGERANT PRESSURES
R32 18.26 264.80 R32 REFRIGERANT PRESSURES
R134A 6.69 96.00 R134 REFRIGERANT PRESSURES
R290 9.78 141.77 R290 PRESSURE CHART [PDF]3
R404A 13.3 190.40 R404A PRESSURE CHART [PDF]4
R407H see R404A / R507 R407H PRESSURE CHART [PDF]5
R410A 17.82 258.42 R410A REFRIGERANT PRESSURES
R448A 11.18 162.07 R448A / N40 PRESSURE CHART [PDF] 6
R449A 10.83 157.02 R449A PRESSURE CHART [PDF] 7
R452A 12.00 173.97 R452A PRESSURE CHART [PDF] 8
R502 12.00 173.97 R502 PRESSURE CHART [PDF] 12
R507 13.57 196.82 R507 PRESSURE CHART [PDF] 11
R600A 3.03 44.00 R600A PRESSURE CHART [PDF] 9
R1234YF 6.82 98.92 R1234YF PRESSURE CHART [PDF] 10
R1234ZW      

Notes to the table above

Definition of Air Conditioner High Side and Low Side Pressures

First let's explain "low-side" and "high-side" air conditioner compressor motor pressures and what they mean.

Air conditioning service manuals and training refer to:

Refrigerant Pressure / Temperature Chart & Table Downloads

 

Typical HVAC Refrigerant Pressures

Photograph of a
commercial air conditioning compressor charging chart

Typical residential air conditioning refrigerant pressures vary depending on the model, compressor motor size and design, and the refrigerant used.

The design pressures may be provided on labels attached to the equipment but the actual air conditioner operating pressure will vary in part as a function of the incoming air temperatures.

"Charging Charts" (such as the commercial unit charging chart shown here) are provided in service manuals to determine the target suction vacuum (negative) pressure and output pressure for a given compressor motor.

Use of the charging chart for the specific compressor is the correct way to service it. The following example pressures are based on "rules of thumb" that get you in the right "ballpark" if no charging chart is at hand.

Example of actual air conditioner compressor high side output pressure:

Using R-22 refrigerant and assuming an outside air temperature of 85 °F called for 120 °F inside the compressor (add 35 °F to incoming air temperature) and an output high-side compressor pressure of about 260 psi.

Example of actual air conditioner low side input or suction line pressure during operation:

Low-side pressure during normal operation of the same compressor model and refrigerant and the same outdoor air temperature of 85 °F called for 45 °F temperature entering the compressor (subtract 40 °F from incoming air temperature) which on the service chart indicates that the incoming or suction line pressure would be about 75 psi.

Example of a more theoretical air conditioner or heat pump pressure and temperature at the compressor and at the cap tube or thermostatic expansion valve: 

During normal operation: at an outdoor temperature of 72 °F, liquid refrigerant (R12 for example) leaving the outdoor condensing coil and entering the cap tube or TEV might be at 100 psi and 95 °F.

These numbers vary by changes in ambient temperature, compressor model, and refrigerant gas used.

On the low side of the TEV or cap tube (in the cooling coil in the air handler) where the liquid refrigerant is changing state to a gas, it may be cooled down to 10 °F. and by the time the refrigerant leaves the cooling coil (evaporator coil) and gets back to the compressor motor it will be all vapor and may be at just 15 psi. [R12 refrigerant changes from liquid to vapor at 14.6 psi at 10 °F.]

Air Conditioner or Heat Pump Refrigerant Equalization Pressure - System-OFF refrigerant pressures

When you measure heat pump or cooling system pressures makes as much difference as where you measure it. When an air conditioning or heat pump system has turned off and been off for some time (30 minutes or more) pressures equalize throughout the system between the high and low sides.

At that point the refrigerant pressure in both the high side and low side of the air conditioner or heat pump system will be in accordance with the ambient air temperature and the properties of the particular refrigerant gas present.

The static or equalized system refrigerant pressure will be defined by the refrigerant gas type (which defines its boiling point and pressure at various temperatures).

For example with that cute old R12 refrigerant, as long as there is just about any refrigerant in the system - enough so that there is some liquid refrigerant, i.e. it's not all just gas) then in equalized condition at 70 psi ambient temperature the refrigerant pressure will be 70 psi.

With a temperature correction chart you can read the static or equalized refrigerant pressure for any refrigerant gas and the actual ambient temperature.

Reminder: this refrigerant gas behavior means that if you use pressure test gauges to measure the refrigerant pressure in the static or equalized air conditioning or heat pump system, the gauges only tell you the refrigerant pressure, not the quantity of refrigerant that is present in the system.

See GAUGE, REFRIGERATION PRESSURE TEST

Correcting Refrigerant Pressure & Leaks

If after review of the above article, you have determined that you have a refrigerant pressure problem or a refrigerant leak, there are procedures to address those issues. These corrections will include getting the right refrigerant charge by any of several means (weight or volume measurements or some techs monitor refrigerant line temperature).

It also means finding and fixing the refrigerant leak if the problem was simply lost refrigerant.

For help with these corrections, see:

Refrigerant Type & Environmental Concerns Update

US HFC Emissions in 2014 - U.S. EPA cited & discussed at InspectApedia.com

Illustration, excerpted from TRANSITIONING TO LOW-GWP ALTERNATIVES in Residential & Light Commercial Air Conditioning [PDF] (live link given just below), U.S. EPA, accounts for an estimated 36.7 metric tons of CO2 equivalent released into the atmosphere by residential and light commercial A/C equipment in 2014.

At COMPARISON of REFRIGERANT GAS PROPERTIES we explained the two most widely-used measures of environmental impact of refrigerant gases, GWP and ODP, and that table makes clear that there are significant differences in both Global Warming Potential and Ozone Depletion Potential among refrigerants.

More about environmental concerns among refrigerants and the move towards refrigerants that offer less contribution to global warming and its costs is in the following articles:

 




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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2023-05-30 by InspectApedia Publisher - NEVER just attach refrigerant gauges to your HVAC compressor/condenser unit if you're not trained and equipped to do so

@Steve Tomms,

Sure.

First, NEVER just attach refrigerant gauges to your HVAC compressor/condenser unit if you're not trained and equipped to do so. It's not just a matter of attaching the gauges and reading pressure.

Proper gauge use procedure requires that you purge air from the gauge set lines before attaching them to the condenser unit - else you may push air (or dirt) into the unit and contaminate it, interfering with proper operation.

Now what the pressures mean depend on the specific refrigerant being used, the ambient temperatures, elevation, and operating state of the machine.

The High and LO pressures on your system might be normal. Nobody can say from just the data in your note. But above on this page you'll see typical pressures for most refrigerants under ambient and other conditions.

When you say that your new AC unit has never worked well, we need to get more specific.

Is airflow inadequate?
Does the supply air never feel cool?

Those are usually rather different problems.

At REPAIR GUIDES A/C / HEAT PUMP - home

we give some typical problem descriptions and diagnostic guides. Take a look there and also let us know what's going on and we can perhaps offer more specific suggestions.

On 2023-05-29 by Steve tomms

Hi, I just had a system installed a week ago. It never worked well. I’m getting the run around from the HVAC company. Today I put a set of gages on that I borrowed. It’s 82 degrees out. On my low side I have 42 and on the high side it’s 220.

Any advice I’d appreciated.

On 2022-05-21 by InspectApedia-911 (mod) - an over-charge could be causing liquid slugging at the compressor: a condition that will destroy it

@Bill Hammer,

Watch out: you might want to turn off the A/C or heat pump unit IMMEDIATELY.

I'm concerned that an over-charge could be causing liquid slugging at the compressor: a condition that will destroy it.

That done,

Let's start by noting just what refrigerant is in-use in your equipment; then you can use the refrigerant tables listed here to see what are the normal and proper operating pressure ranges for the refrigerant in your equipment.

And I'd want an on-site tech to track down the banging: is it a compressor problem, an expansion valve issue, another control?

On 2022-05-21 by Bill Hammer

new air condition units increased the pressure in the lines from approximately 300 PSI to 400 PSI causing the pipes to make a heck of a banging noise inside the wall.. Any solutions

On 2022-05-21 by InspectApedia-911 (mod) - Set the refrigerant charge to the specifications for the heat pump per its IO manual, NOT the compressor's data tag

@Toby Bo,

I hesitated to reply earlier because, frankly, I don't want to pretend to know more than I do about this topic.

My first thought was to say "Set the refrigerant charge to the specifications for the heat pump per its IO manual, NOT the compressor's data tag. The compressor may be used in a wide range of cooling systems while the whole heat pump assembly has properties and thus specifications that are model-dependent and are specified by its manufacturer.

Here are more detailed thoughts about your question:

In general, the refrigerant charge pressures MUST be read in the context of:

- the ambient temperatures
- altitude in some locations
- empirical data: such as your observation of gas bubbles in the refrigerant line
- temperature measurements at specific locations on the high and low side refrigerant lines

While I agree that it sounds as if the refrigerant charge was low, in diagnosing your complaint that it takes too long to cool down the building interior, I would want some more objective data such as

- the temperature drop across the cooling coil
- the air velocity measured at the supply registers in the poorly-cooled area
- a check of the poorly-cooled area for other problems such as abnormal heat gain, air leaks, an open window that nobody noticed, etc.
- a check for a malfunctioning refrigerant-metering device like a TEV

It'll be embarrassing if we go to a lot of trouble fooling with refrigerants only to find later that the air filter was clogged or a supply duct crushed or disconnected.

I like the diagnostic steps at LOST COOLING CAPACITY inspectapedia.com/aircond/Air_Conditioner_Diagnosis.php

Once we've got what appears to be a proper refrigerant charge I'd still go back for those objective data measurements.

Note on refrigerant charge: OPINION - while techs commonly use temperature measurements on the suction line to adjust the refrigerant charge, the ONLY way to put exactly the right refrigerant quantity into an HVACR system is to evacuate it and then put in the specific refrigerant quantity specified by the manufacturer, adjusted if necessary for extra lengths of refrigerant piping.

On a commercial or larger residential cooling system that uses a refrigerant receiver, the charge can be imprecise and below factory-specified, but sufficient to work. On smaller equipment including home appliances like refrigerators, freezers, window A/C units, the charge needs to be more-precise.

Finally: if your system used to work adequately but has stopped doing so, and if you trace the problem to an actual loss of refrigerant, then you need to find and fix the leak. Just adding refrigerant from time to time is a poor (if common) practice, contaminates the environment, and in some situations may be illegal.

Keep me posted - what you find will help other readers.

On 2022-05-21 by Toby Bo

Hello-My R22 heatpump condenser with a scroll compressor has a label on the service plate that states 278/144 psi charge. The install manual for the exact model 10HPB24-11P has a table that states 210/74 psi charge @ 85F.This is quite a difference on the suction pressure.

The plate says R22 and was installed in 2005 when R22 was available. I do not know the original pressure at install. The sightglass was full of bubbles until I raised pressure to 185/70 @ 75F.The air temp drop inside is a wimpy 13F from intake to outlet and runs way too long 50-90 minutes.

Can I increase suction pressure that much?

On 2022-05-11 by Inspectapedia Com Moderator - My home AC system is short cycling

@Peter,

Just a couple of guesses,

your service tech might look at the thermostatic expansion valve to make sure that it's not freezing or frosting up.

Then of course she'll probably check the refrigerant charge.

On 2022-05-10 by Peter

Question. My home AC system is short cycling. The low pressure is around 70psi system off. When system runs pressure drops below 30 and system turns off. That cycle repeats

Any thoughts?

On 2021-12-23 by Inspectapedia Com Moderator - Is r32 gas ozone friendly?

@George,

Check the ODL and GWP ratings in the first table on this page.

On 2021-10-20 by George

is r32 gas ozone friendly

On 2021-09-21 by inspectapedia.com.moderator

@Khan,

Sorry I'm not familiar with that phrase - "back pressure" - and out of context am not sure what to make of it.

But on this page you'll find

R32 REFRIGERANT PRESSURE / TEMPERATURE CHARTS

that probably give you the pressure ranges about which you're asking.

On 2021-09-21 by Khan

R32 back pressure ?

On 2021-09-02 by inspectapedia.com.moderator (mod) - convert any temperature expressed in degF or Farenheit to degC or Celsius

@decha chatngern,

A simple formula that lets you convert any temperature expressed in degF or Farenheit to degC or Celsius is

(Temp°F − 32) × 5/9 = Temp°C

Example:

If the temperature is 32F:

(32°F − 32) × 5/9 = 0°C

On 2021-09-02 by decha chatngern

Hello, how can we convert a table to Celsius?

On 2021-07-16 by inspectapedia.com.moderator (mod) - pressures and temps are too high

@rich,

I agree that your pressures don't look right;

For an R22 system, high-side pressure is typically about twice the ambient temperature, plus 50 PSI.

At 98 degF ambient outdoor air temperature that would be (98 x 2 ) + 50 or 196 + 50 = 246 psi. high side pressure

The low side pressure for R22 at 98 degF ambient air temp ought to be just a bit above 30 psi.

1. First and most common cause for abnormally high high side or "head pressure" in an A/C or heat pump system is abnormally-hot air entering the compressor/condenser unit.

Where is your installation: country, city, climate, and what is it sun exposure;

After all in many countries including the U.S., global warming has led to some extreme conditions recently, reaching record of 134F in Death Valley.

Aside from that number one cause of high head pressure, check for the following:

2. Is the condensing coil blocked by crud? I've seen leaves, mown grass, even locust tree blossom fibres completely blocking an evaporator coil air inlet.

3. see our complete list of causes of high head pressure at REFRIGERANT HIGH HEAD PRESSURE DIAGNOSIS

On 2021-07-16 by rich

I have a Trane condenser and furnace. I have a 3 ton condenser. my low side pressure is 85psi/50 degree temp., high side is 415psi/156 degree temp., its r-22 system my wet bulb is 71 degrees, my air temp. at the condenser is 98 degrees,temp. is 72 degrees at the vapor line. that gives me the propper subcooling but the pressures and temps. are too high. 415psi is too high so is 85psi on the low side isnt it.

On 2020-10-25 by (mod) - What is the working gas pressure for R22 in the air conditioner?

R22 REFRIGERANT PRESSURES will show what pressures are found with R22 refrigerant

On 2020-10-25 by Kenny Mkandawi

What is the working gas pressure for R22 in the aircon

On 2020-07-19 - by (mod) -

Anon

You can find your refrigerant pressure in the article and references above, but you'll see you have to name the specific refrigerant gas and the ambient temperature.

On 2020-07-18 by Anonymous

How many suction gas pressure in 11 tr ac

Reader Question: what is the pressure in an A/C or heat pump system when the compressor is off?

Hi, I always wondered, car or house A/C, if it is off, compressor off, is there any pressure in the system? Or does the compressor cause and make the pressure? Thanks, J.K [email 26 Sept 2015]

I would assume less pressure in system when compressor is off then when on? Thanks, John Kelly. PS: Just had new condenser / compressor unit put in my house and when running, see small drip on lower line seems to be diluted oil. Possibly just condensation mixed with oil that got on while repairing. It don't seem to get that small drop when I don't run it. Its on the bottom of that weld spot.

Reply:

Absolutely there is pressure in the air conditioning or heat pump system when the compressor is not running.

When the compressor shuts off the high side pressure is high - say 200 and the low side low - say 20 (these are just conceptual as actual pressure depends on the compressor, ambient temperature, refrigerant type).

Then when the motor stays off for a time - say 1/2 hour more or less - *normally* pressure in the whole system equalizes to a lower number which would be the pressure that the particular refrigerant would sit at for the current ambient temperature (at sea level).

E.g. R22 at 80 °F will stabilize at 143.7 psi in the system while R410 would be at 235.9 psi.

Watch out: about that OIL DRIP: is bad if it's really leaking. There is oil in the refrigeration system (to lube the compressor); if there is oil leaking out at a fitting on the refrigerant line then there is most likely also an actual refrigerant leak.

If you clean the joint - wipe it clean of oil and condensation - you should not see more oil there. Condensate yes.


Question: refrigerant pressure differences in an inverter-type air conditioner system?

2016/08/29 Y.W. asked [ by private email to editor ]

Hi, firstly I want to thank you for creating such a helpful site - keep it up!

I just have a few questions regarding inverter A/Cs - In a split-type home air conditioner which use an inverter compressor, does this effect the PSI needed on either the high or low side of the system?

If so how do I know what it is supposed to be? Is the method for adding refrigerant different for inverters than a standard system? and is there a way to know at any point in time if the compressor is running at full speed or only partly?
Thank you

Reply:

The psi you'd expect to see in any HVACR system is a function of:

1. the specific refrigerant used

2. the ambient temperature

3. the compressor having reached steady state or run long enough that the low side and high side pressures are being controlled by the refrigerant metering device such as the TEV

For any specific refrigerant you'll find a chart that gives the relationship of refrigerant pressures to temperature - as the tech has to consider that when charging the system.

The data tag and specs for a given compressor model and brand will also often give the standard working pressure range.

For other readers, an "inverter" in an air conditioning system is a variable speed control that changes the pumping speed of the AC compressor motor in response to the temperature in the conditioned space.

By varying the compressor speed we vary the rate at which refrigerant is dispensed into the cooling system. In my OPINION this is a sophistication of an air conditioning design that relies only on the refrigerant metering device (TEV or cap tube) to dispense refrigerant into the cooling system.

Inverter designs do not only rely on varying the compressor motor speed.

Motor on/off cycling, configurations that bypass refrigerant hot gas output from the high-side over to the low side or suction side of the system, mechanically operated refrigerant control valves, and other approaches allow for an inverter type air conditioner or heat pump design.

The purpose of an inverter type air conditioner system is to match the compressor's output to variations in the cooling load on the system, presumably producing a more efficient cooling system.

These systems may also be described as VRF or variable refrigerant flow designs.

I've researched this question further but not yet found specifications indicating that the refrigerant operating pressures are different with an inverter or VRF air conditioning or heat pump design. I have found warnings that lower refrigerant velocity can result in lubrication problems in the compressor and a reduced compressor life.

Heatcraft warns:

Compressor Operating Limits:

Compressors should not be operated outside of the operating limits shown on the published compressor specification sheets, and low pressure controls should not be set below the minimum settings without prior written approval of the Copeland Application Engineering Department.

Operating below the allowable minimum suction pressure may result in excessive discharge temperatures which can cause cylinder and valve damage, and may result in lubrication problems. Since high discharge temperatures can occur even though the motor is cool, the motor thermostat will not protect the compressor against these conditions.

Operation of motor-compressors beyond the established recommended operating limits will be considered misuse and abuse, and damage may result.

- source: Heatcraft, "Why and How we Use Capacity Control " [PDF], Heatcraft Refrigeration Products – North America, 2175 West Park Place Blvd. Stone Mountain, GA 30087
United States of America Tel: (770) 465-5600 Toll-Free: (800)-321-1881 hrpd.feedback@heatcraftrpd.com retrieved 2016/08/29, original source: www.heatcraftrpd.com/res/pdfs/faqs/Capacity_Control.pdf
This company has offices world wide.

 

More Notes About Residential Air Conditioner Compressor Pressures

Put another way, high temperature or high pressure on the air conditioner low side is a sign of a problem. That is, as pressure on the high side goes way up, low side pressure will increase as well, and we may exceed the operating temperature of the system.

The Low side temperature must be low enough to get transfer of heat from the indoor air into the evaporator coil. The High Side temperature must be high enough to get transfer of heat into the outdoor air.

If your air conditioning or heat pump system has lost its cooling capacity or won't start see REPAIR GUIDE for AIR CONDITIONERS.

...

Continue reading at REFRIGERANT PRESSURE DIAGNOSIS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see REFRIGERANT PRESSURE READING & CHART FAQs - questions & answers posted originally at this page.

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