# Hot Topics: R22 Gauge Readings

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reed - Visiting Guest

What should the readings be for R22 system , ambient temp 90 degrees. Also, I am familiar with R12, but what are the inside readings for R22 ? The farthest outside reading is PSI.

lynn comstock - Visiting Guest

How to read gauges IF EVERYTHING IS NORMAL.

Real understanding of the gauges comes when you forget pressures and think about the temperatures of the boiling or condensing refrigerant…or you can skip to the information in CAPS.

The gauge reading are always influenced by:

1) Outdoor temperature.

2) Indoor temperature.

3) Refrigerant (usually R-22).

4) Airflow across the outdoor coil (about 1000 cfm per ton).

5) Airflow across the indoor coil (about 400 cfm per ton).

6) The efficiency of the system (a design issue).

7) Running time…it takes 8 to 10 minutes for the system to arrive at steady state conditions. Interpretation of the gauges depends on equilibrium (steady state) in the system.

IF these factors are normal, the coils are clean, the compressor is OK/normal, the metering device is OK/normal, the components are matched and designed to work together (LOTS OF IFS)...and assuming the refrigerant is R-22:

The head (high side) pressure depends on the TEMPERATURE at which the refrigerant (R-22) condenses in the condenser (outdoor coil). Add 15 to 25 degrees F to the outdoor temperature (say 90+15=105 and 90+ 25=115) and look at the TEMPERATURE information for R-22 on the gauge (green ring of numbers).

THE HIGH SIDE NEEDLE SHOULD POINT TO A TEMPERATURE BETWEEN 105 AND 115 (in the green ring of numbers) AND THE PRESSURE IS READ ON THE BLACK RING OF NUMBERS FOR PRESSURE.

The suction pressure depends by the TEMPERATURE of the boiling (evaporating) refrigerant (R-22) in the evaporator (indoor or cooling coil). This temperature should be about 35 to 40 degrees F below the Return Air temperature. IF the return temperature is 75 the evaporating temperature of the R-22 should be between (75-40=35) and (75-35=40).

THE LOW SIDE NEEDLE SHOULD POINT BETWEEN 35 AND 40 DEGREES (in the green ring of numbers) FOR R-22 AND THE PRESSURE IS READ WHERE THE NEEDLE POINTS ON THE BLACK RING OF NUMBERS FOR PRESSURE.

These TEMPERATURE rules apply to any refrigerant used for comfort cooling...even one that you are seeing for the first time in your life.

reed - Visiting Guest

Thank you for the very very fast response. Good information in your reply, thank you.

Here is what I have at this point:

My guages read correctly, but not cooling. I would expect the high pressure line to be HOT, it is luke warm. The low sie isjust cool to the touch, not very cold. Also, I don't have any condensation at all..... The outside unit was just replaced, completely. The inside unit was disassembled and cleaned and the fan motor replaced.

Any suggestions?

KField - Member

What do you mean by 'gauges read correctly'? If refrigerant is vaporizing, heat is being absorbed. So there is no possibility that pressures are good and no cooling is going on. If there is no condensation on the outdoor suction it is possible that you are low on refrigerant. If the wrong metering device is installed or the outdoor unit does not match the indoor unit, you will have improper cooling and pressures that are not appropriate. Maybe you could tell us what the indoor and outdoor temps are and what the pressures are.

Ed Imeduc - Member

AC

IF you are EPA now I dont see why you ask this and dont know how to read the gauges. If your not EPA you shouldnt be putting gauges on a unit anyhow. ED

lynn comstock - Visiting Guest

Gauge info is not enough.

The tech should get ALL of the following nine items of DATA and tell you his opinion of the problem and solution:

Outdoor ambient- condenser air entering temperature

Outdoor condenser air leaving temperature

Return air temperature- air temperature entering the indoor coil

Supply air temperature- air temperature leaving the indoor coil

The wet bulb temperature of the return air