What Should R-407C Pressures Be?
Typical R-407C suction and discharge ranges for residential and light commercial AC. Pressures sit ~5-10% above R-22 across the envelope. Glide (~11°F) requires dew-curve superheat and bubble-curve subcooling measurement.
Saturation pressure ≠ operating pressure
The numbers below are operating pressures — what your manifold gauges read on a running system at a given outdoor ambient. Operating pressures depend on charge, ambient, indoor load, superheat, and subcooling. The R-407C saturation pressures are different — those are thermodynamic equilibrium values you can look up on the R-407C PT chart.
Operating pressure ranges
| Condition | Suction (low side) | Discharge (high side) | Superheat target | Subcooling target |
|---|---|---|---|---|
| Residential AC at 75°F outdoor (R-22 retrofit) | 55–70 PSIG | 175–220 PSIG | 8–15°F | 8–14°F |
| Residential AC at 85°F outdoor | 60–75 PSIG | 220–270 PSIG | 8–15°F | 8–14°F |
| Residential AC at 95°F outdoor (rating condition) | 65–80 PSIG | 260–320 PSIG | 8–15°F | 8–12°F |
| Residential AC at 105°F outdoor | 70–85 PSIG | 305–370 PSIG | 10–18°F | 6–12°F |
| Residential AC at 115°F outdoor (hot-climate extreme) | 75–90 PSIG | 350–425 PSIG | 10–20°F | 5–10°F |
Source: ASHRAE Handbook of Refrigeration 2022 (R-22 retrofit guidance); Honeywell Genetron R-407C technical service literature; Chemours Suva 407C product data; equipment OEM R-22 to R-407C retrofit procedures (Trane, Carrier)
R-407C operating pressures sit about 5-10% above R-22 across the operating envelope, which is consistent with R-407C's design intent as an R-22 retrofit refrigerant. Service equipment rated for R-22 is appropriate for R-407C from a pressure-rating standpoint (both well below 500 PSI high-side maximum).
Two things distinguish R-407C from R-22 in field service. First, R-407C requires POE oil where R-22 uses mineral oil — the retrofit involves an oil change, not just refrigerant replacement. Second, R-407C has substantial temperature glide (~11°F at typical evaporator pressures) where R-22 has none. This matters for service measurement: use the dew curve for superheat (suction line) and the bubble curve for subcooling (liquid line). Using a single curve for both produces a systematic error equal to the glide.
The site's [superheat calculator](/superheat-calculator/) and [subcooling calculator](/subcooling-calculator/) handle this automatically when R-407C is selected. PT charts that show both bubble and dew columns (which all of this site's R-407C charts do) make manual verification possible.
R-407C saturation pressure quick reference
Saturation pressure at common service temperatures, from the verified PT dataset (CoolProp 7.2.0). Use this for quick mental cross-reference against your manifold readings — operating pressure on a running system varies around these saturation values based on charge, ambient, and load.
| Temperature | Bubble (PSIG) | Dew (PSIG) | PSIA | kPa gauge |
|---|---|---|---|---|
| -20°F | 13.7 | 6.5 | 28.4 | 95 |
| 0°F | 29.5 | 19.4 | 44.2 | 203 |
| 20°F | 51.2 | 37.9 | 65.9 | 353 |
| 40°F | 80.2 | 63.2 | 94.9 | 553 |
| 70°F | 140.5 | 117.3 | 155.2 | 969 |
| 95°F | 209.4 | 181.0 | 224.1 | 1444 |
| 120°F | 298.6 | 265.8 | 313.3 | 2059 |
R-407C saturation curve over the service temperature range. Source: CoolProp 7.2.0 (REFPROP-compatible Helmholtz EOS), generated 2026-06-05.
Operating envelope across application conditions
Operating pressure ranges visualized — suction (blue) and discharge (red) bars at each application condition. Wider bars indicate larger variation expected; tighter bars indicate the operating point is more constrained.
R-407C property snapshot
| Safety class | A1 |
| Type | hfc blend |
| GWP (IPCC AR5, 100-yr) | 1774 |
| ODP | 0 |
| Normal boiling point | -46.5°F |
| Critical temperature | 187.1°F |
| Critical pressure | 658 PSIG |
| Temperature glide | 11.0°F |
| Lubricant compatibility | POE |
| AIM Act affected | Yes |
Real service scenarios for R-407C
Three field scenarios showing common diagnostic patterns when reading R-407C system pressures. Each maps manifold readings to a verdict and specific service action.
Properly-charged R-407C system at design ambient
Scenario · Residential R-407C TXV-equipped AC system, 95°F outdoor, 75°F indoor return air. System has been running 15-20 minutes at steady state and you're confirming charge.
R-407C undercharge — high SH + low SC fingerprint
Scenario · Same R-407C TXV system, six months later. Customer reports weak cooling on a 95°F day. You take readings to confirm what's going on.
R-407C overcharge — low SH + high SC fingerprint
Scenario · R-407C TXV system after a service add by gauge feel rather than weight. Compressor running noisy and customer reports higher power bills.
Operating envelope and equipment context — R-407C
R-407Cpressures sit inside an operating envelope bounded by the refrigerant's thermodynamic properties (saturation curve, critical point) and the equipment's pressure-rated components. Understanding both bounds tells you what pressure readings are normal versus what readings indicate a system fault.
- Saturation envelope: R-407C saturation pressure ranges from 14 PSIG at −20°F to 209 PSIG at 95°F. Critical temperature is 187.1°F — above this point no saturation state exists.
- Equipment pressure rating: R-407C critical pressure is 658 PSIG. Per AHRI Standard 540-2020, the high-pressure cutout switch is typically set at approximately 85% of critical pressure to protect the compressor from running into the near-critical regime where small temperature swings produce large pressure excursions. For R-407C, that's a practical cutout setpoint around 559 PSIG.
- Charging metric: R-407C is zeotropic with 11.0°F glide. TXV systems charge by subcooling using the bubble curve at discharge pressure; superheat measurement uses the dew curve at suction pressure. Wrong-curve selection introduces error equal to the glide value.
- Lubricant requirement: R-407C runs on POE lubricant. POE oil is hygroscopic — keep cylinder sealed, change filter-drier on every service visit, evacuate to ≤500 microns before recharging to remove residual moisture.
- Regulatory status: R-407C is subject to the EPA AIM Act phase-down (40 CFR Part 84). Service supply continues from reclaimed and allocated production, with prices rising as supply tightens. Plan refrigerant cost escalation over equipment lifetime.
Common R-407C measurement mistakes
- PSIG vs PSIA confusion. Service manifold gauges read PSIG; tables sometimes use PSIA. PSIA = PSIG + 14.696. Confusing the two shifts saturation lookups by ~5°F at low-side pressures.
- Wrong curve for R-407C. R-407C is zeotropic with 11.0°F glide. Use the dew curve at suction pressure for superheat, bubble curve at discharge for subcooling. Wrong-curve selection introduces error equal to the glide value.
- Probing temperature without insulating. Ambient air pulls the reading toward room temperature, inflating apparent superheat or depressing apparent subcooling.
- Reading before steady state. Allow 10-20 minutes after compressor start for pressures and temperatures to stabilize.
- Treating saturation as operating. Saturation is the thermodynamic reference; operating pressure on a running system depends on charge, ambient, load, superheat, and subcooling.
When pressures fall outside R-407C normal range
Use the calculators on this site to convert your readings into superheat, subcooling, and diagnostic patterns:
- Superheat Calculator — suction PSIG + line °F → superheat for R-407C.
- Subcooling Calculator — liquid PSIG + line °F → subcooling.
- Combined SH/SC/PT — both sides + pattern-matching diagnostic banner.
- System Pressure Diagnostic — multi-input diagnostic with approach temperatures.
- High head pressure causes — decision tree for high-side problems.
Diagnostic procedure
Step-by-step procedure to interpret R-407C pressure readings on a service call. Emitted as HowTo structured data for search-engine rich results.
1Confirm refrigerant type before connecting gauges
Check the equipment data plate. R-407C systems may be original-OEM (less common — most R-407C systems are R-22 retrofits) or marked with a retrofit conversion label. Mismatched gauge connections waste time and risk cross-contamination if the wrong refrigerant has been added during prior service.
Tools: Equipment data plate inspection, Service history review
2Measure outdoor ambient and indoor return-air temperatures
Outdoor dry-bulb at the condenser unit (avoid direct sun); indoor return-air dry-bulb at the air handler. AHRI rating conditions: 95°F outdoor / 80°F indoor.
Tools: Outdoor dry-bulb thermometer, Indoor return-air thermometer
3Read low-side and high-side pressures with R-22-rated manifold
R-22-rated 500 PSI manifolds are appropriate for R-407C pressure-wise. Let the system run 10-15 minutes under load before recording. Record both suction and discharge pressures simultaneously.
Tools: R-22 or R-407C-rated manifold gauge set (500 PSI minimum)
4Compute superheat using the DEW curve
For R-407C, the dew curve gives the saturation temperature at the suction-line measurement point (where the refrigerant has fully vaporized). Bubble-curve saturation at the same pressure is the evaporator-INLET saturation, which is wrong for superheat measurement. The superheat calculator handles this when R-407C is selected — manual calculation requires reading the dew column on the PT chart.
Tools: Contact temperature probe with insulation, PT chart with bubble + dew columns or superheat calculator
5Compute subcooling using the BUBBLE curve
For R-407C, the bubble curve gives the saturation temperature at the condenser-OUTLET measurement point (where the refrigerant has fully condensed). Dew-curve saturation at the same pressure is the condenser-INLET saturation, which is wrong for subcooling measurement. The subcooling calculator handles this when R-407C is selected.
Tools: Contact temperature probe with insulation, PT chart with bubble + dew columns or subcooling calculator
6Compare to expected ranges; diagnose using the standard pattern
Same four diagnostic patterns apply as for any HFC refrigerant: low SH + high SC = overcharge; high SH + low SC = undercharge; high SH + high SC = restriction or low evap airflow; low SH + low SC = airflow or metering device issue. The [combined PT/SH/SC calculator](/pt-superheat-subcooling-calculator/) flags the pattern automatically.
Frequently asked
›What's the normal operating pressure of R-407C at 95°F outdoor?
Expect roughly 65-80 PSIG suction and 260-320 PSIG discharge on a properly-charged R-407C residential AC system at the 95°F rating condition. The exact values depend on indoor return-air temperature, superheat, subcooling, and the specific equipment. Use the operating range table above to compare to your readings.
›How does R-407C pressure compare to R-22?
Very close — R-407C operates about 5-10% higher across the envelope. R-407C at 95°F outdoor is ~65-80 PSIG suction / 260-320 PSIG discharge vs. R-22's ~65-80 PSIG suction / 250-300 PSIG discharge. R-22-rated service equipment is appropriate for R-407C. The substantive operational difference is glide (R-407C has ~11°F; R-22 has none) and lubricant (R-407C requires POE; R-22 uses mineral oil).
›Why does R-407C have temperature glide?
R-407C is a ternary HFC blend: 23% R-32, 25% R-125, 52% R-134a by mass. The three components have different vapor pressures, so the blend has bubble (saturated liquid) and dew (saturated vapor) temperatures that differ by ~11°F at typical operating pressures. This is normal for zeotropic blends. R-22 is a pure refrigerant — single component, no glide.
›How does glide affect my superheat reading?
If you use the single saturation curve (treating R-407C like a pure refrigerant), you'll get a superheat value that's wrong by ~10°F — apparent superheat is higher than actual superheat. Use the DEW curve for superheat measurement on R-407C. The dew temperature at the suction pressure is the boundary above which refrigerant is fully vapor and superheated. Our [superheat calculator](/superheat-calculator/) uses the dew curve automatically when R-407C is selected.
›What lubricant does R-407C use?
Polyolester (POE) oil. Mineral oil (R-22's lubricant) is incompatible — mixing produces sludge formation and accelerated wear. R-22 to R-407C retrofit requires an oil change (typically 2-3 oil-flush cycles to bring mineral oil residual below 5%). POE oil is hygroscopic, so moisture management during service is critical (vacuum to 500 microns, filter-drier replacement).
›Is R-407C being phased out?
Yes, gradually, under the EPA AIM Act. R-407C's GWP of 1774 is well above the 700-GWP threshold for new residential AC equipment beginning January 1, 2025. New equipment uses R-32 or R-454B. R-407C remains legal for service of existing equipment indefinitely under current rules, but new equipment installations have shifted to A2L alternatives. For systems facing major work, full replacement with new R-32/R-454B equipment is increasingly cost-effective.
›Can I service R-407C with R-22 gauges?
Pressure-wise, yes — R-22 500 PSI manifolds handle R-407C's operating envelope without issue. Cross-contamination concern: any residual R-22 in the gauges may slightly affect R-407C charging accuracy. For service work where charging accuracy matters, dedicated R-407C gauges or thoroughly-purged manifolds are preferred. Recovery cylinders should be R-407C-dedicated to prevent cross-contamination of the recovered refrigerant.
R-407C full reference
Saturation chart, properties, retrofit guidance.
Superheat Calculator
Suction PSIG + line °F → superheat.
Subcooling Calculator
Liquid PSIG + line °F → subcooling.