HVAC Pressure Temperature Chart & Calculator

Interactive PT Chart Calculator

Select a refrigerant and convert in either direction: gauge pressure (PSIG) to saturation temperature, or temperature to pressure. Results are interpolated linearly from the verified chart below. The calculator will not extrapolate outside the −40°F to 150°F data range.

Pressures are PSIG at sea level. R-22 and R-410A results are dew-point based (R-410A glide is under 0.3°F). R-404A results show both bubble point (use for subcooling) and dew point (use for superheat). No JavaScript? Use the full static chart below.

R-410A & R-22 Pressure Temperature Chart

Every HVAC technician needs an accurate PT chart in their pocket. The table below covers −40°F to 150°F and shows the relationship between saturation temperature (°F) and gauge pressure (PSIG) for the three most common refrigerants. We have highlighted two chart checkpoints that come up constantly in exam problems and field checks.

R-410A PT Chart Checkpoints

• Blue (40°F): A common evaporator saturation temperature for A/C — about 118 PSIG on R-410A.
• Orange (105°F–110°F): A common condensing saturation range — about 341–365 PSIG on R-410A.

R-22 PT Chart Checkpoints

• At a 40°F evaporator saturation temperature, R-22 reads about 69 PSIG — roughly half the R-410A pressure at the same temperature.
• At a 105°F condensing saturation temperature, R-22 reads about 211 PSIG.

*Pressures are in PSIG at sea level (14.696 psia). R-22 and R-410A columns are dew-point values; R-410A’s temperature glide is under 0.3°F, so a single column applies to both superheat and subcooling work. R-404A is a zeotropic blend: use the Liquid/Bubble column for subcooling and the Vapor/Dew column for superheat.
Data source: computed with the open-source CoolProp thermophysical property library (REFPROP-comparable equations of state), rounded to 0.1 PSIG. Last verified: July 4, 2026.

How to Read a PT Chart for R410A

Understanding the basics is crucial. A standard R-410A PT chart tells you the "Saturation Temperature." This is the temperature where the refrigerant is changing state (boiling from liquid to vapor, or condensing from vapor to liquid).

When your gauge manifold reads a specific pressure (e.g., 118.4 PSIG on R-410A), you look at the chart to find the corresponding saturation temperature (40°F). If the actual pipe temperature matches this, the system is saturated. You can also use the calculator above to interpolate between chart rows.

What Is Saturation Temperature in HVAC?

Saturation temperature is the temperature at which a refrigerant changes phase (boils or condenses) at a given pressure. While refrigerant is changing state, pressure and temperature are locked together — know one, and the PT chart gives you the other. That locked relationship is the entire reason your gauges are useful: a gauge only measures pressure, but the PT relationship converts it into a temperature you can compare against real pipe measurements.

Two saturation temperatures matter on a running system:

• Evaporating temperature (low side): the saturation temperature that corresponds to your suction pressure.
• Condensing temperature (high side): the saturation temperature that corresponds to your liquid-line (head) pressure.

How to Find Saturation Temperature in 3 Steps

• Step 1: Connect your gauge manifold to the service port (low side for evaporating temperature, high side for condensing temperature).
• Step 2: Read the gauge pressure in PSIG.
• Step 3: Convert pressure to temperature using the calculator or the chart above.

Calculating Superheat & Subcooling

You cannot charge a system correctly without calculating these values. You simply cross-reference the pressure on your R-410A PT chart to find the saturation temp, then use these formulas:

Measure Superheat at the suction line (low side) and Subcooling at the liquid line (high side).

1. Superheat (Fixed Orifice)

Ensures only vapor enters the compressor.

• Formula: Actual Suction Line Temp - Saturation Temp (from chart) = Superheat.
• Target: Typically 10°F - 20°F (Check manufacturer specs).

2. Subcooling (TXV)

Ensures a full column of liquid reaches the metering device.

• Formula: Saturation Temp (from chart) - Actual Liquid Line Temp = Subcooling.
• Training range: 8°F - 12°F is a common teaching range — the manufacturer’s nameplate or charging data always takes precedence.

Superheat Calculator (Actual)

Enter your suction pressure and the measured suction line temperature. The calculator finds the saturation temperature from the verified chart and subtracts it for you.

Subcooling Calculator (Actual)

Enter your liquid line (high side) pressure and the measured liquid line temperature.

Target Superheat: When and How to Use It

This method applies to fixed-orifice (piston) systems only. TXV-equipped systems maintain superheat on their own and are charged by subcooling instead. For a fixed-orifice system, the correct superheat is not one number — it moves with the load, so you calculate a target from two field measurements:

• Outdoor dry-bulb temperature (ODB) — measured in the shade at the condenser air inlet.
• Indoor return-air wet-bulb temperature (IWB) — measured at the return grille with a wet-bulb or psychrometer reading.

A long-standing industry rule of thumb taught in NATE prep estimates the target as Target Superheat = (3 × IWB − 80 − ODB) ÷ 2. Manufacturer charging charts, where available, always take precedence over this formula.

The formula is supported for roughly 55–115°F outdoor dry-bulb and 50–76°F indoor wet-bulb. If the computed target falls below 5°F, conditions are outside what superheat charging can resolve reliably — verify with the manufacturer’s data instead.

High Side vs Low Side: What a PT Chart Can and Cannot Tell You

On the low side (suction line), your gauge pressure converts to the evaporating saturation temperature. On the high side (liquid line), it converts to the condensing saturation temperature. Those two numbers — combined with real line temperatures — are what superheat and subcooling are built from.

What a PT chart cannot tell you is a universal “normal” operating pressure. Actual pressures on a healthy system move with:

• Outdoor dry-bulb temperature and indoor temperature/humidity (load).
• Airflow: filter condition, blower speed, duct restrictions, coil cleanliness.
• Equipment design and efficiency rating — a high-SEER condenser runs a lower condensing temperature than an older standard-efficiency unit.
• Metering device type (fixed orifice vs TXV) and refrigerant charge.

A classroom example with every assumption stated: a correctly charged, mid-efficiency R-410A air conditioner, indoor air 75°F at ~50% RH, outdoor 95°F, clean coils, rated airflow, might show a suction pressure around 115–125 PSIG (about 38–42°F evaporating) and a head pressure around 340–390 PSIG (about 105–115°F condensing). Change any assumption and these numbers legitimately change — this is a teaching example, not a diagnostic table.

You may also hear the old rule that condensing temperature runs about 20–30°F above outdoor temperature. That range described older standard-efficiency condensers; modern high-SEER units with larger coils often condense only 15–20°F over ambient. Treat it as a historical rough check, never a law. The reliable way to judge a charge is superheat and subcooling compared against the manufacturer’s charging data.

PT Chart Practice Problems (Worked Examples)

These are the exact styles of question you will see on EPA 608 and NATE exams. All answers use the same verified data as the chart and calculator above; small differences against other published charts come down to rounding rules.

Example 1: Pressure to Saturation Temperature

“Saturated R-410A at a pressure of 95 PSIG will change state at a temperature of…?”

• Step 1: 95 PSIG falls between the chart rows 87.4 PSIG (25°F) and 97.0 PSIG (30°F).
• Step 2: Interpolate: (95 − 87.4) ÷ (97.0 − 87.4) = 0.79 of the way up a 5°F step ≈ 4°F above 25°F.
• Answer: about 29°F. Exam charts that use coarser rounding may list 30°F — go with the chart your exam provides.

Example 2: Working Backwards from Superheat

“The evaporator outlet temperature on an R-410A system is 50°F and the evaporator superheat is 10°F. What is the evaporating pressure?”

• Step 1: Saturation temperature = outlet temperature − superheat = 50°F − 10°F = 40°F.
• Step 2: Convert 40°F to pressure on the R-410A chart.
• Answer: about 118 PSIG (118.4 PSIG on our chart).

Example 3: Condensing Temperature from Head Pressure

“What is the approximate condensing temperature of an R-22 system operating at 195 PSIG?”

• Step 1: 195 PSIG falls between the chart rows 181.8 PSIG (95°F) and 195.9 PSIG (100°F).
• Step 2: 195 PSIG is nearly at the 100°F row, so no math is really needed.
• Answer: about 100°F (99.7°F interpolated).

Want more? Our practice app includes hundreds of PT chart, superheat, and subcooling problems with step-by-step answer explanations — start a free practice test.

Bubble Point vs. Dew Point (The "Glide")

For single-component refrigerants like R-22 or near-azeotropic blends like R-410A, the boiling and condensing temperatures are essentially the same at a given pressure. However, for Zeotropic blends (like R-404A or R-407C), there is a "Temperature Glide." That is why our chart lists separate Liquid/Bubble and Vapor/Dew columns for R-404A.

• Bubble Point (Liquid): Use this when calculating Subcooling.
• Dew Point (Vapor): Use this when calculating Superheat.

Unlike older blends, reading a R-410A PT chart is simple because R-410A has near-zero glide, behaving like a single component.

R-22 vs R-410A: No Drop-In Conversion

The chart above makes the pressure difference obvious: at a 40°F evaporating temperature, R-22 runs about 69 PSIG while R-410A runs about 118 PSIG; at a 105°F condensing temperature it is roughly 211 vs 341 PSIG. R-410A systems operate at about 50–60% higher pressure across the working range.

• Different oil: R-22 systems typically use mineral oil; R-410A requires POE oil. The two lubricants are not interchangeable.
• Different hardware: compressors, coils, and line components on an R-22 system are not rated for R-410A pressures.
• “Conversion charts” are comparison charts. A side-by-side PT table helps you compare readings — it is not a procedure for putting R-410A into an R-22 system. There is no direct drop-in conversion; retrofits require a manufacturer-approved procedure and, usually, a designated retrofit refrigerant.

HVAC P-T Chart FAQ

What is an HVAC P-T chart?

An HVAC P-T chart is a pressure-temperature reference that shows the saturation temperature of a refrigerant at a given pressure. Technicians use it to diagnose charge, superheat, subcooling, and system conditions.

How do I read an R410A pressure temperature chart?

Find the measured R410A pressure in PSIG, then read across to the matching saturation temperature. Use that temperature with your measured line temperature to calculate superheat or subcooling.

What is the difference between superheat and subcooling?

Superheat compares suction line temperature to evaporator saturation temperature. Subcooling compares liquid line temperature to condenser saturation temperature. Both require a pressure-temperature chart reading.

Do I use bubble point or dew point for superheat?

Use dew point for superheat and bubble point for subcooling when working with blends that have temperature glide. R410A has near-zero glide, so the difference is usually minimal.

What is saturation temperature in HVAC?

Saturation temperature is the temperature at which a refrigerant changes phase at a given pressure. On a PT chart every pressure corresponds to one saturation temperature, so technicians read suction or liquid pressure and convert it to a temperature for superheat and subcooling calculations.

What should the high and low side pressures be for R410A?

There is no single normal pressure. Operating pressures depend on outdoor and indoor temperatures, humidity, airflow, equipment efficiency, and the metering device. Instead of chasing a fixed number, measure superheat and subcooling and compare them with the manufacturer's charging data.

What is the target superheat for R410A?

On fixed-orifice systems, target superheat is calculated from indoor return wet-bulb and outdoor dry-bulb temperatures; a common field estimate is (3 x IWB - 80 - ODB) / 2. TXV systems are charged by subcooling instead. Manufacturer charging charts always take precedence.

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