R-134a Pressure Chart: How to Actually Read the Pressures

At 32 °F saturation, R-134a reads about 28 psig; at 40 °F, about 35 psig; at 100 °F, about 124 psig. R-134a is a single compound with no temperature glide, so one column is exact. Use low-side pressure for superheat and liquid-line pressure for subcooling. Which EPA rules apply depends on the equipment: a car is Section 609, a refrigerator or chiller is Section 608.

People searching for this chart are usually either working on a car or working on a refrigerator, a walk-in or a chiller. The pressure-temperature relationship is identical in all of them, because it is a property of the refrigerant, not the machine. What changes is the law around the service valve. Most R-134a charts online ignore that entirely, and a technician who reads one is left thinking the rules for a pickup truck and a 300-pound chiller barrel are the same. They are not.

What are the actual R-134a pressures?

These come from the Arkema Forane 134a Pressure Temperature Chart, which was generated from the NIST REFPROP database. Pressures are psig. R-22 is shown for comparison, from the R-22 PT chart.

Temperature	R-134a	R-22
0 °F	6.5 psig	24.0 psig
10 °F	11.9 psig	32.8 psig
20 °F	18.4 psig	43.1 psig
30 °F	26.1 psig	55.0 psig
32 °F	27.8 psig	—
35 °F	30.4 psig	—
40 °F	35.0 psig	68.6 psig
45 °F	40.1 psig	—
50 °F	45.4 psig	84.1 psig
60 °F	57.4 psig	101.6 psig
70 °F	71.1 psig	121.4 psig
80 °F	86.7 psig	143.6 psig
90 °F	104.3 psig	168.4 psig
100 °F	124.2 psig	195.9 psig
110 °F	146.4 psig	226.4 psig
120 °F	171.2 psig	260.0 psig
130 °F	198.7 psig	—
140 °F	229.2 psig	—
150 °F	262.9 psig	—

R-134a boils at roughly −15 °F at atmospheric pressure. The Arkema chart shows 0.1 psig at −15 °F, and below about −16 °F the values switch to inches of mercury vacuum. That is why R-134a is used for medium-temperature work and not for low-temperature freezers: run the evaporator much below zero and the low side goes into a vacuum, which pulls air and moisture in through any leak.

Why are R-134a pressures so much lower than R-22 or R-410A?

Because R-134a is a less volatile refrigerant. At 40 °F it sits at about half the pressure of R-22 and under a third of R-410A.

EPA uses exactly this property to sort refrigerants. Under the pressure classes in 40 CFR 82.152, a medium-pressure appliance uses a refrigerant with a liquid-phase saturation pressure between 45 and 170 psia at 104 °F. On the Arkema chart, R-134a is 132.8 psig at 104 °F, or roughly 147.5 psia once you add atmospheric pressure. That places it in the medium-pressure class alongside R-12, while R-22 and R-410A are high-pressure. The class matters, because it sets how deep you recover before opening the system (see the table further down).

Why does an R-134a chart only need one column?

R-134a is a single compound, 1,1,1,2-tetrafluoroethane (HFC-134a). A pure substance boils and condenses at one temperature for each pressure, so there is no dew point and bubble point to separate and no glide.

That makes the single column exact. It is also why R-134a is a useful comparison when you learn blends. R-404A contains R-134a as one of its three components, and it is the mix of components with different boiling points that gives the R-404A PT chart its two columns.

Which reading do you use for superheat and subcooling?

Calculation	Pressure you read	Temperature you measure
Superheat	Low side, at the suction service port	Suction line, near the same point
Subcooling	High side, liquid line	Liquid line, at the condenser outlet

Convert the pressure to a saturation temperature, then do the subtraction. Superheat is measured suction-line temperature minus saturation temperature. Subcooling is saturation temperature minus measured liquid-line temperature. Say the low side reads 30 psig: the chart puts that at about 35 °F. If the suction line measures 45 °F, you have about 10 °F of superheat. What each reading actually tells you covers how to interpret the combinations.

Many automotive systems use an orifice tube or an expansion valve and are charged by weight to a label value rather than by superheat or subcooling. The chart still tells you what the refrigerant is doing inside the evaporator and condenser, and that is how you diagnose from gauges.

What should R-134a pressure be on a 90-degree day?

There is no single right number, and a chart that gives you one is guessing.

Suction pressure follows the evaporator temperature, which moves with load, airflow and humidity. Head pressure follows the condensing temperature, which sits above outdoor ambient by an amount set by the condenser's design, its cleanliness and the airflow across it. In a car, engine speed and whether the vehicle is moving change it too. What the chart tells you is that 104.3 psig corresponds to 90 °F saturation. That is the standing pressure of an idle system that has equalized at 90 °F. It is not a running pressure.

For a running system, compare your converted readings with the manufacturer's service information. That is what defines the correct charge, not a rule of thumb.

What does R-134a standing pressure tell you?

With the system off long enough to equalize, both sides read the saturation pressure at the refrigerant's temperature: about 71 psig at 70 °F and 87 psig at 80 °F.

A standing pressure close to the chart value confirms there is still liquid R-134a in the system. A reading well above it suggests non-condensables or a different refrigerant. It says nothing about how much refrigerant is in there: a system with a small amount of liquid left reads the same saturation pressure as a full one.

Is R-134a work Section 608 or Section 609?

It depends on the appliance, not the refrigerant. EPA 608 vs 609 covers the split in detail.

Equipment running R-134a	Certification that applies	Recovery requirement
Car or light truck air conditioning (MVAC)	Section 609	Recovery and recycling under Subpart B
Open-drive AC on farm or construction equipment, 20 lb charge or less (MVAC-like)	Section 608 Type II or Section 609, per 82.161(a)(1)(v)	Not covered by Table 1
Domestic refrigerator, water cooler, vending machine (5 lb or less, factory sealed)	Section 608 Type I	90% or 80% recovery, or 4 in Hg, under 82.156(b)
Walk-in, reach-in or other commercial system	Section 608 Type II	10 in Hg under 200 lb; 15 in Hg at 200 lb or more
Centrifugal or screw chiller	Section 608 Type II	10 in Hg under 200 lb; 15 in Hg at 200 lb or more

The Table 1 levels in 40 CFR 82.156 shown above are for recovery equipment made on or after November 15, 1993. With a machine made before that date, the medium-pressure level is 4 inches. That date refers to when the recovery machine was manufactured, not the age of the refrigerator or chiller. Those levels are also deeper than the 0 inches required for R-22 or R-410A systems under 200 pounds, which catches technicians used to high-pressure work. How to recover refrigerant walks through the procedure.

Two other points apply to every R-134a system. Venting it is prohibited under 40 CFR 82.154(a), because the prohibition has covered substitute refrigerants such as HFCs since November 15, 1995. And sales are restricted to certified technicians, with one exception described on EPA's sales restriction page: R-134a for car AC sold in a container of two pounds or less with a self-sealing valve can still be sold for do-it-yourself use.

Does a leak repair rule apply to R-134a?

Not the Section 608 rule. 40 CFR 82.157 reaches appliances with 50 pounds or more of an ozone-depleting refrigerant. R-134a is an HFC with no chlorine, so it is outside it.

The AIM Act rule, yes, since January 1, 2026. EPA's Emissions Reduction and Reclamation program at 40 CFR 84.106 covers appliances with 15 pounds or more of a refrigerant containing an HFC, per EPA's leak repair fact sheet. A walk-in or chiller on R-134a can easily cross that line. The AIM Act explainer covers the rest of that law.

What this means on the job

Before you read the gauges, know two things: which refrigerant is in the system, and which rulebook applies to the equipment. The chart is the same for a truck and a chiller. Your certification, your recovery target and your leak repair duties are not.

Then work the numbers the same way every time. Take both pressures and both line temperatures, convert with the chart, calculate superheat or subcooling, and compare against the manufacturer's figures. On stationary R-134a equipment, remember that it is medium-pressure: recovery goes to 10 or 15 inches of vacuum with a modern machine, not to 0. Pulling a 500-micron dehydration vacuum before recharging is good practice, but it is not the Section 608 recovery requirement. That distinction shows up on the exam, and the Type II practice test is where it is tested most.

Frequently asked questions

What are normal AC pressures for R-134a?

There is no fixed normal value. The chart converts pressure to temperature. A low side around 30 psig means the refrigerant in the evaporator is boiling at about 35 °F, and a high side around 124 psig means it is condensing at about 100 °F. Whether that is correct depends on load and ambient, so compare against the manufacturer's service data.

What should R-134a pressure be at 90 degrees?

At 90 °F saturation, R-134a is 104.3 psig according to the Arkema chart. That is what an idle, equalized system reads at 90 °F, not a running pressure. With the system running, the high side sits above that because the refrigerant condenses above ambient temperature, and the low side sits well below it.

What is the pressure of R-134a at 30 degrees?

At 30 °F saturation, R-134a is 26.1 psig on the Arkema chart, and at 32 °F it is 27.8 psig. Those are the readings where an evaporator is operating at or near freezing. If the low side runs below that for long, moisture on the coil can freeze and cut airflow.

Does R-134a have temperature glide?

No. R-134a is a single compound, HFC-134a, so it boils and condenses at one temperature for each pressure. Its chart needs only one column, and that column is exact. Blends that contain R-134a, such as R-404A, do have glide, which is why their charts print separate liquid and vapor values.

Do I need EPA 608 or 609 certification to work on R-134a?

It depends on the equipment. Car and light-truck air conditioning needs Section 609. Domestic refrigerators and other small appliances need Section 608 Type I, and commercial refrigeration and chillers need Type II. Open-drive systems on farm and construction equipment accept either. Neither certification currently expires.

Is R-134a high pressure or low pressure?

Neither, under EPA's classes. R-134a is a medium-pressure refrigerant, with a saturation pressure between 45 and 170 psia at 104 °F. Medium-pressure appliances are Type II work, and with modern recovery equipment the required recovery level is 10 inches of mercury under 200 pounds and 15 inches at 200 pounds or more.

Sources

• Arkema, Forane 134a Pressure Temperature Chart
• 40 CFR 82.152, Definitions
• 40 CFR 82.154, Prohibitions
• 40 CFR 82.156, Proper evacuation of refrigerant from appliances
• 40 CFR 82.157, Appliance maintenance and leak repair
• 40 CFR 82.161, Technician certification
• 40 CFR 84.106, Leak repair
• EPA, Leak Repair Requirements for Appliances Containing HFCs and Certain Substitutes (fact sheet, January 2026)
• EPA, Refrigerant Sales Restriction