R22 PT Chart: Pressure-Temperature Guide for Refrigeration

If you're still working on legacy R22 systems, you know that guessing the charge is a quick way to ruin a perfectly good compressor. An r22 pt chart isn't just a piece of paper for your clipboard; it’s the primary diagnostic tool that tells you exactly what pressure your suction and discharge lines should show based on the ambient temperature. When the numbers on your manifold gauges don't align with the saturation temperatures on this chart, you’re looking at a system struggling with airflow, non-condensables, or a refrigerant leak. Don't fly blind. Use this data to verify your charge accurately.

Reading the R22 Pressure-Temperature Table

The chart above maps PSIG against temperature, showing the precise boiling point of R22 at specific pressures. To get a useful reading, it's requisite to match your gauge pressure to the corresponding saturation temperature. If your low-side gauge reads 60 PSIG, the table shows a saturation temperature of roughly 34°F. If the actual pipe temperature is significantly higher than that, you’ve got a problem with your superheat calculation—likely a restriction or a low charge. Precision matters.

Common Pitfalls in the Field

Technicians often forget that outdoor ambient temperature changes how the system settles. Measuring pressure while the sun is beating directly on the condenser coils can skew your readings by 10 to 15 PSIG, leading you to believe the system is overcharged when it’s actually just hot. Always shade your gauges or wait for the system to stabilize before making a final call. Another trap is ignoring the gauge calibration itself. If your manifold needles don't sit at zero when the system is off, every other reading you take is worthless. Check your gear before you touch the refrigerant.

Temperature (°F)	Pressure (PSIG)
0	24
5	28
10	32
15	37
20	42
25	48
30	54
35	61
40	68
45	76
50	84
55	93
60	103
65	113
70	124
75	136
80	148
85	161
90	176
95	191
100	207
105	224
110	242
115	261
120	281
125	302
130	325
135	348
140	373
145	399
150	427
155	456
160	487
165	519
170	553

Interpreting the Saturation Curve

Reading the chart requires matching your gauge pressure to the corresponding temperature. Look at the -40°F row; it shows a pressure of just 0.8 PSIG. This extreme low indicates you're dealing with a vacuum state, which is why seeing anything below 0 PSIG on a standard gauge is a massive red flag for air or moisture contamination. If your system is pulling a vacuum when it should be running, you’ve got a major restriction in the liquid line.

Moving toward the higher end of the spectrum, check the 130°F mark. The data hits 346.2 PSIG here. This is where high-side pressures live during a sweltering summer day. If your gauges show 346 PSIG while the ambient air is nowhere near 130°F, your condenser coils are likely choked with dirt or the fan motor is failing. The system is fighting to shed heat. It’s working way too hard.

Interpolation is a reality of the field. If your gauge reads 150 PSIG, you won't find that exact number on the chart. You'll see 148.0 PSIG at 70°F and 160.7 PSIG at 75°F. You’re sitting right in the middle—roughly 71°F. Don't sweat the decimals. Being within a degree or two is usually fine for diagnostics.

Pressure Spikes and System Health

Temperature shifts aren't linear, and that’s where technicians get tripped up. Look at the jump from 0°F to 5°F. The pressure climbs from 28.8 PSIG to 34.2 PSIG—a 5.4 PSIG increase. Now, look at the jump from 120°F to 125°F. The pressure moves from 306.0 PSIG to 326.0 PSIG—a 20 PSIG surge. The system is far more sensitive to pressure changes at higher temperatures. A small overcharge at high ambient temperatures creates massive pressure spikes that can blow a seal or trip a high-pressure switch.

Keep these points in mind when you’re out in the field:

• The 100°F Milestone: At 234.5 PSIG, you're at a standard benchmark for high-side pressure on a warm day. If you’re consistently hitting this at 80°F ambient, stop and check your airflow.
• The Low-Side Floor: Seeing 19.5 PSIG at -10°F is normal for deep-freeze applications. In a standard residential AC unit, seeing this number is an instant indicator of a frozen evaporator coil.
• Gauge Accuracy: Always verify your manifold against the chart at ambient temperature before starting the unit. If the gauge doesn't match the ambient air temperature on the chart, your baseline is wrong.

Avoiding Common Diagnostic Traps

The biggest mistake is ignoring the altitude. These numbers assume sea level. If you're working at 5,000 feet, your absolute pressures will shift. You have to account for the thinner air affecting the condenser's ability to reject heat. If you don't adjust your expectations, you'll end up "chasing the ghost" by adding refrigerant to a system that’s already properly charged.

Print this chart and keep it inside your gauge bag. Don't rely on your memory. When you're on a hot roof and the customer is hovering, it’s easy to misread a digit. Having the hard numbers in front of you keeps the diagnosis objective. It keeps you from guessing. Trust the math, not your gut.

Mastering Superheat and Subcooling

Calculating superheat and subcooling is where the chart stops being a reference and starts being a diagnostic engine. To find your superheat, subtract the saturation temperature—found on your chart using your suction pressure—from the actual temperature of the suction line. If you’re seeing a superheat value below 5 degrees, you’re flirting with liquid slugging. That’s a death sentence for your compressor. A high superheat value, say above 20 degrees, usually screams "low refrigerant." Your evaporator is starving. It’s not cooling the air because it’s not boiling enough refrigerant.

Subcooling follows the same logic on the high side. Take the liquid line temperature and subtract it from the saturation temperature found at your discharge pressure. A low subcooling number often points to a restricted metering device or a low charge. If your numbers don't add up, don't just dump more gas in. Check your airflow first. Dirty filters or a blocked blower wheel can fake a charge issue every single time. It’s a common trap.

Pro Tips for Field Accuracy

• Calibrate before you connect: Before you even touch a valve, zero out your manifold gauges. If your needles are off by even 2 PSI, your entire calculation is compromised. It’s the difference between a perfect charge and a wasted afternoon.
• Shade your sensors: Sunlight hitting your temperature probes will give you false high readings. Use a piece of foam or a rag to cover your sensor on the copper line. Keep it shielded.
• Watch for non-condensables: If your pressures are consistently higher than the chart dictates despite clean coils and proper airflow, you likely have air or nitrogen trapped in the system. You’ll need to recover, evacuate, and recharge. There’s no shortcut here.

Frequently Asked Questions

Why is my gauge showing a different temperature than the chart?
Most likely, you’re looking at the wrong scale or your gauge isn't calibrated. Double-check that you're using the R22 scale, not R410A. They aren't interchangeable. Check your gauge calibration.

Does altitude change how I read the chart?
Yes. At higher elevations, the atmospheric pressure is lower. This affects your absolute pressure readings. You’ll need to adjust your target pressures accordingly, or you’ll end up undercharging the system.

Is R22 still legal to use?
R22 production ended years ago. You can only use recycled or reclaimed refrigerant now. It’s expensive and strictly regulated. Handle every ounce with care—don't let it vent.

Keep Your Data Close

You don't want to be fumbling with a smartphone while you're balancing on a ladder. Having a physical copy in your tool bag saves time and keeps you focused. You can download the PDF version of this R22 PT chart right here to keep on your device, or print this chart out and laminate it for your service kit. Having the hard numbers in your pocket means you never have to guess. Keep this reference handy for every legacy system you service—it’s the most reliable partner you’ll have on the job.

[Download High-Resolution R22 PT Chart PDF]