Free Refrigerant PT Chart for HVAC/R Technicians
Free Refrigerant PT Chart for Australian HVAC/R Technicians
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Use this free refrigerant PT chart to convert refrigerant pressure to saturation temperature, or saturation temperature to pressure, for common air conditioning and refrigeration refrigerants.
This page is designed for HVAC/R technicians, refrigeration mechanics, apprentices, service teams and BMS technicians who need a quick pressure-temperature reference while fault finding, commissioning or servicing equipment.
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A PT chart is commonly used when checking evaporating temperature, condensing temperature, superheat, subcooling, refrigerant charge, expansion valve operation, condenser performance and evaporator load.
The chart should always be used with accurate pressure gauges, pipe temperature readings and the correct refrigerant selected for the system.
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These values are intended as a practical field reference only. Always confirm final readings against the correct manufacturer service manual, refrigerant data, site conditions, Australian safety requirements and approved service procedures.
How to Use a Refrigerant PT Chart
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Confirm the refrigerant type
Before using a PT chart, confirm the refrigerant listed on the equipment nameplate. Do not assume the refrigerant based only on the unit age or application. Common HVAC/R refrigerants include R32, R410A, R134a, R404A, R407C and older R22 systems.
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Measure the system pressure
Connect suitable gauges or digital probes and record the suction and discharge pressures. Make sure the system is operating under stable conditions before comparing readings.
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Convert pressure to saturation temperature
Use the PT chart to convert suction pressure to evaporating saturation temperature and discharge pressure to condensing saturation temperature. These saturation temperatures are then compared with actual pipe temperatures to calculate superheat and subcooling.
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Calculate superheat
Superheat is calculated by subtracting the evaporating saturation temperature from the actual suction line temperature. High or low superheat can indicate charge issues, airflow problems, load problems, expansion valve issues or restrictions, depending on the system type.
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Calculate subcooling
Subcooling is calculated by subtracting the actual liquid line temperature from the condensing saturation temperature. Low or high subcooling can help identify refrigerant charge issues, condenser performance problems, restrictions or liquid stacking.
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Refrigerant PT Chart Examples
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Example 1: Calculating superheat
If the suction pressure converts to an evaporating saturation temperature of 4°C, and the measured suction line temperature is 10°C, the superheat is:
10°C minus 4°C equals 6°C superheat.
This result should then be compared with the manufacturer’s expected operating range for the system type, load condition and metering device.
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Example 2: Calculating subcooling
If the discharge or liquid pressure converts to a condensing saturation temperature of 45°C, and the measured liquid line temperature is 38°C, the subcooling is:
45°C minus 38°C equals 7°C subcooling.
This result can help confirm whether liquid refrigerant is being supplied correctly to the expansion device, but it must be assessed with airflow, condenser condition, ambient temperature and system load.
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Common Refrigerants Covered
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R32 PT chart
R32 is commonly used in modern split systems, ducted air conditioners and light commercial air conditioning equipment. When using an R32 PT chart, confirm the correct pressure units and always follow safe handling requirements for mildly flammable A2L refrigerants.
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R410A PT chart
R410A is common in many split systems, ducted systems, package units and VRV/VRF air conditioning systems. It operates at higher pressures than many older refrigerants, so correct gauges, hoses and pressure ratings are important.
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R134a PT chart
R134a is often found in chillers and some refrigeration applications. A PT chart can help technicians compare evaporating and condensing conditions against chilled water temperatures, condenser water temperatures and equipment load.
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R404A PT chart
R404A has been widely used in commercial refrigeration systems. When assessing R404A systems, confirm the system condition, refrigerant history, leak repairs and any retrofit or replacement refrigerant requirements.
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R407C PT chart
R407C is used in some older air conditioning and chiller applications. As a zeotropic blend, technicians should understand dew point and bubble point references when calculating superheat and subcooling.
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R22 PT chart
R22 is an older refrigerant still found in some legacy equipment. When working on R22 systems, confirm current refrigerant regulations, service requirements and whether the system has been converted to an alternative refrigerant.
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Common PT Chart Mistakes
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Using the wrong refrigerant
Always confirm the refrigerant on the unit nameplate or service documentation. Selecting the wrong refrigerant in a PT chart will give incorrect saturation temperatures.
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Charging by pressure only
Pressure alone does not confirm correct refrigerant charge. System load, airflow, water flow, ambient temperature, superheat, subcooling and manufacturer requirements must also be considered.
Ignoring pipe temperature
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A PT chart gives saturation temperature. To calculate superheat or subcooling, you still need accurate suction line and liquid line temperature readings.
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Not allowing the system to stabilise
Readings taken immediately after startup or after a control change may be misleading. Allow the system to run under stable conditions before recording final readings.
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Confusing dew point and bubble point
Some refrigerant blends require different saturation references for superheat and subcooling. Always use the correct chart reference for the refrigerant and calculation being performed.
Assuming one pressure is always correct
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There is no single correct suction or discharge pressure for every system. Correct operating pressure depends on refrigerant type, load, ambient temperature, airflow, water flow, coil condition, compressor operation and system design.
Refrigerant PT Chart FAQs
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What is a refrigerant PT chart?
A refrigerant PT chart is a pressure-temperature chart used to convert refrigerant pressure into saturation temperature, or saturation temperature into pressure. It is commonly used during HVAC and refrigeration fault finding, servicing and commissioning.
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What does PT stand for in refrigeration?
PT stands for pressure-temperature. In refrigeration and air conditioning, pressure and saturation temperature are directly related for a given refrigerant.
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Can I use a PT chart to charge a system?
A PT chart can help with charging checks, but it should not be used on its own. Correct charging should consider manufacturer procedures, weighed charge, superheat, subcooling, airflow, water flow, load and ambient conditions.
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What is the difference between superheat and subcooling?
Superheat compares suction line temperature to evaporating saturation temperature. Subcooling compares condensing saturation temperature to liquid line temperature. Both values help technicians understand how the refrigerant circuit is operating.
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Why are my PT chart readings different from the unit manual?
Differences can occur due to pressure units, gauge accuracy, refrigerant blend reference, operating load, sensor location, elevation, system design or incorrect refrigerant selection. Always confirm against the correct manufacturer data.
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Which refrigerants should I include on a HVAC PT chart?
For Australian HVAC/R service work, useful refrigerants to include are R32, R410A, R134a, R404A, R407C and R22, along with any other refrigerants commonly used on the equipment being serviced.
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Is R32 pressure higher than R410A?
R32 and R410A both operate at high pressures compared with older refrigerants such as R22. Always use the correct PT chart for the refrigerant installed in the system rather than comparing different refrigerants directly.
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What causes high superheat?
High superheat can be caused by low refrigerant charge, restricted refrigerant flow, low evaporator load, poor airflow, blocked filters, expansion valve issues or incorrect sensor readings. It should always be diagnosed with the full system condition, not one reading only.
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What causes low superheat?
Low superheat can be caused by overfeeding, low load, poor evaporator heat transfer, expansion valve problems, incorrect airflow, sensor placement issues or possible liquid floodback. Confirm the expected range for the equipment before making adjustments.
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What causes low subcooling?
Low subcooling can indicate low refrigerant charge, flashing liquid, condenser issues, high load, refrigerant feed problems or incorrect measurement points. Confirm with manufacturer data and other system readings.
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What causes high subcooling?
High subcooling can be caused by overcharge, restrictions, liquid stacking, condenser flooding, incorrect fan control or metering device issues. Always compare subcooling with head pressure, liquid line temperature, airflow or water flow and system load.