R404A Operating Pressures

Hi, I’m Nathan. I’ve worked as an HVAC and refrigeration technician for over 10 years, and I’ve put my gauges on a lot of R404A systems: walk in freezers, walk in coolers, prep tables, reach ins, and remote condensing units.

If you’re here because you want the real answer to “What should my R404A pressures be?”, you’re thinking the right way but there’s one important catch:

R404A operating pressures depend heavily on the evaporator temperature, the condensing temperature, the load, airflow, and ambient temperature. So instead of giving you one magic suction and head pressure, I’m going to show you:

• The normal pressure ranges I actually see in the field
• How to use an R404A PT chart correctly (dew vs bubble matters)
• A detailed R404A PT chart (dew and bubble pressures)
• Quick troubleshooting when pressures look wrong

If you’re a homeowner: please use this as education and basic diagnostics. Handling refrigerant typically requires licensing, and guessing with pressure alone is one of the fastest ways to damage a compressor.

What is R404A and why does the PT chart show two pressures?

R404A is a refrigerant blend (a zeotropic mix). Because it’s a blend, it doesn’t behave like a single pure refrigerant at saturation. That’s why you’ll see two saturation points:

• Dew point (vapor) pressure/temperature
  Use this for evaporator saturation temperature and superheat calculations.
• Bubble point (liquid) pressure/temperature
  Use this for condensing saturation temperature and subcooling calculations.

In plain English

When you’re checking the suction side and superheat, you care about what the vapor is doing (dew).
When you’re checking the liquid line and subcooling, you care about what the liquid is doing (bubble).

That one detail alone is where I see a lot of people get misled.

Quick answer: Typical R404A operating pressure ranges (real world)

These are common ballpark ranges I see when systems are running correctly. They are not “always correct” numbers, because the correct number is tied to target evaporating and condensing temperatures.

Typical R404A pressures by application

Application	Typical Evap Temp (SST)	Typical Suction Pressure	Typical Condensing Temp (SCT)	Typical Head Pressure
Low temp freezer (walk in freezer, -10°F box)	-40°F to -20°F	10 to 30 psig	90°F to 120°F (varies by ambient)	200 to 320+ psig
Medium temp cooler (walk in cooler, 35°F box)	15°F to 30°F	35 to 55 psig	90°F to 120°F	220 to 350+ psig

What I personally expect on many walk in freezers

A lot of properly running R404A freezers land around:

• Suction: 10 to 20 psig (often close to 10 to 15 psig depending on design)
• Head: ~220 to 300+ psig depending on ambient and condenser cleanliness

R404A pressure is not a “charge indicator” by itself

One of the most important things I’ve learned over the years is this:

You do not charge R404A by “target pressure.”
You charge/diagnose by:

• Superheat (evaporator feeding)
• Subcooling (condenser and liquid feed)
• System design (TXV vs cap tube), ambient, airflow, load, and defrost performance

Typical targets I use as a starting point

These vary by equipment and manufacturer, but as a general field starting point:

Metering Device	What to set/verify	Typical Target Range
TXV / EEV	Evaporator superheat	6°F to 12°F (common starting range)
TXV / EEV	Subcooling	8°F to 15°F (common starting range)
Cap tube / fixed orifice	Total superheat	Often higher and more variable

Always defer to the manufacturer charging chart when you have it.

How to use the R404A PT chart (step by step)

Step 1: Decide if you need dew or bubble

• Suction pressure -> use Dew to get evaporator saturation temperature (SST)
• Head pressure -> use Bubble to get condensing saturation temperature (SCT)
• Liquid line temp -> Bubble is used for subcooling
• Suction line temp -> Dew is used for superheat

Step 2: Convert pressure to saturation temperature

Use the PT chart to convert psig to °F saturation.

Step 3: Calculate superheat and subcooling

• Superheat = suction line temperature – SST (dew)
• Subcooling = SCT (bubble) – liquid line temperature

Real example (simple)

Let’s say on an R404A freezer you measure:

• Suction pressure: 15 psig
• Suction line temp at evaporator outlet: 5°F

From the PT chart, 15 psig is around -22°F dew saturation (you’ll verify exact with chart).
So superheat is: 5 – (-22) = 27°F superheat (that’s high for many TXV systems, and it would make me start checking feeding, restriction, or low charge depending on the full picture).

Useful R404A stats (EEAT details that matter)

Here are a few facts that come up constantly when you’re working with R404A:

Item	Value (commonly referenced)	Why you should care
ODP (ozone depletion potential)	0	Doesn’t deplete ozone like older CFCs/HCFCs
GWP (global warming potential, 100 year)	about 3920	One of the reasons it’s being phased down
Blend behavior	Temperature glide exists	Dew and bubble are different, affects charging/diagnosis
Charging method	Charge as liquid	Helps prevent blend fractionation

If you work on refrigeration, you already know R404A is widely targeted for phasedown/transition to lower GWP options (depending on your region). That doesn’t change the fact that a huge amount of equipment in the field still runs it.

R404A PT Chart (Bubble and Dew Pressures)

Important notes before you use this chart

• Values are provided as a practical reference. Your gauge set or manufacturer PT chart should be the final authority.
• Pressures are listed in psig (gauge pressure), not psia.
• Bubble = liquid saturation, Dew = vapor saturation.

R404A PT Chart (°F to psig) Part 1: -49°F to 0°F

Temp °F	Bubble psig	Dew psig
-49	0.9	0.3
-48	1.3	0.7
-47	1.7	1.2
-46	2.1	1.6
-45	2.6	2.0
-44	3.0	2.4
-43	3.5	2.9
-42	4.0	3.4
-41	4.4	3.8
-40	4.9	4.3
-39	5.4	4.8
-38	5.9	5.3
-37	6.4	5.8
-36	7.0	6.3
-35	7.5	6.8
-34	8.0	7.4
-33	8.6	7.9
-32	9.2	8.5
-31	9.7	9.0
-30	10.3	9.6
-29	10.9	10.2
-28	11.5	10.8
-27	12.2	11.4
-26	12.8	12.0
-25	13.4	12.7
-24	14.1	13.3
-23	14.8	14.0
-22	15.4	14.6
-21	16.1	15.3
-20	16.8	16.0
-19	17.5	16.7
-18	18.3	17.4
-17	19.0	18.2
-16	19.8	18.9
-15	20.5	19.7
-14	21.3	20.4
-13	22.1	21.2
-12	22.9	22.0
-11	23.7	22.8
-10	24.6	23.6
-9	25.4	24.5
-8	26.3	25.3
-7	27.1	26.2
-6	28.0	27.0
-5	28.9	27.9
-4	29.8	28.8
-3	30.8	29.8
-2	31.7	30.7
-1	32.7	31.6
0	33.7	32.6

R404A PT Chart Part 2: 1°F to 50°F

Temp °F	Bubble psig	Dew psig
1	34.7	33.6
2	35.7	34.6
3	36.7	35.6
4	37.7	36.6
5	38.8	37.7
6	39.8	38.7
7	40.9	39.8
8	42.0	40.9
9	43.1	42.0
10	44.3	43.1
11	45.4	44.3
12	46.6	45.4
13	47.8	46.6
14	49.0	47.8
15	50.2	49.0
16	51.5	50.2
17	52.7	51.5
18	54.0	52.7
19	55.3	54.0
20	56.6	55.3
21	57.9	56.6
22	59.3	58.0
23	60.6	59.3
24	62.0	60.7
25	63.4	62.1
26	64.8	63.5
27	66.3	64.9
28	67.8	66.4
29	69.2	67.8
30	70.7	69.3
31	72.3	70.8
32	73.8	72.4
33	75.4	73.9
34	77.0	75.5
35	78.6	77.1
36	80.2	78.7
37	81.8	80.3
38	83.5	82.0
39	85.2	83.7
40	86.9	85.4
41	88.6	87.1
42	90.4	88.8
43	92.2	90.6
44	94.0	92.4
45	95.8	94.2
46	97.6	96.0
47	99.5	97.9
48	101.4	99.8
49	103.3	101.7
50	105.3	103.6

R404A PT Chart Part 3: 51°F to 100°F

Temp °F	Bubble psig	Dew psig
51	107.2	105.6
52	109.2	107.6
53	111.2	109.6
54	113.3	111.6
55	115.3	113.6
56	117.4	115.7
57	119.5	117.8
58	121.7	119.9
59	123.8	122.1
60	126.0	124.2
61	128.2	126.4
62	130.5	128.7
63	132.7	130.9
64	135.0	133.2
65	137.3	135.5
66	139.7	137.8
67	142.0	140.2
68	144.4	142.6
69	146.9	145.0
70	149.3	147.4
71	151.8	149.9
72	154.3	152.4
73	156.8	154.9
74	159.4	157.5
75	162.0	160.1
76	164.6	162.7
77	167.3	165.3
78	170.0	168.0
79	172.7	170.7
80	175.4	173.4
81	178.2	176.2
82	181.0	179.0
83	183.8	181.8
84	186.7	184.7
85	189.5	187.5
86	192.5	190.4
87	195.4	193.4
88	198.4	196.4
89	201.4	199.4
90	204.5	202.4
91	207.6	205.5
92	210.7	208.6
93	213.8	211.7
94	217.0	214.9
95	220.2	218.1
96	223.4	221.4
97	226.7	224.6
98	230.0	227.9
99	233.4	231.0
100	236.8	234.6

R404A PT Chart Part 4: 101°F to 150°F

Temp °F	Bubble psig	Dew psig
101	240.2	238.1
102	243.6	241.5
103	247.1	245.0
104	250.6	248.5
105	254.2	252.1
106	257.8	255.6
107	261.4	259.3
108	265.1	262.9
109	268.8	266.6
110	272.5	270.4
111	276.3	274.1
112	280.1	278.0
113	284.0	281.8
114	287.9	285.7
115	291.8	289.6
116	295.8	293.6
117	299.8	297.6
118	303.8	301.7
119	307.9	305.8
120	312.1	309.9
121	316.3	314.1
122	320.4	318.3
123	324.7	322.5
124	329.0	326.8
125	333.3	331.2
126	337.7	335.6
127	342.1	340.0
128	346.6	344.4
129	351.1	349.0
130	355.7	353.5
131	360.2	358.1
132	364.9	362.8
133	369.6	367.5
134	374.3	372.2
135	379.1	377.0
136	383.9	381.9
137	388.8	386.8
138	393.7	391.7
139	398.7	396.7
140	403.7	401.7
141	408.8	406.8
142	413.9	412.0
143	419.1	417.1
144	424.3	422.4
145	429.6	427.7
146	434.9	433.1
147	440.3	438.5
148	445.8	443.9
149	451.3	449.5
150	456.8	455.1

What causes abnormal R404A pressures? (Field troubleshooting I use)

Here’s a practical “what it often means” guide. You still have to confirm with temperatures, airflow, and superheat/subcooling.

If suction is low

Common causes:

• Low refrigerant charge
• Restricted liquid line filter drier
• TXV underfeeding (bulb issue, loss of charge, plugged screen)
• Starved evaporator due to low load or iced coil
• Evaporator fan issues (reduced airflow)

What I check next:

• Superheat (usually high if it’s starved)
• Frost pattern on evaporator
• Temp drop across filter drier

If suction is high

Common causes:

• Warm box / heavy load (doors open, product load)
• Defrost problems causing warm coil
• TXV overfeeding
• Compressor valve issues (less common but real)

What I check next:

• Box temp and return air temp
• Superheat (may be low if overfeeding)
• Compressor amperage and capacity symptoms

If head pressure is high

Common causes:

• Dirty condenser coil
• Bad condenser fan or fan cycling issue
• Non condensables (after poor evacuation)
• Overcharge
• High ambient temp / poor condenser location

What I check next:

• Condenser split (SCT vs ambient)
• Subcooling (overcharge usually drives subcooling high)
• Airflow through condenser and coil condition

If head pressure is low

Common causes:

• Low ambient with no head pressure control (common on outdoor units)
• Undercharge
• Flooded condenser (depending on controls)
• Low load

What I check next:

• Whether the unit has headmaster/flooding valve controls
• Liquid feed stability
• Subcooling and sight glass (if equipped)

FAQ: R404A operating pressures