By means of pressure reading:
Pressure
Data
Circuit
Too low
A little low
Normal
A little high
Too high
Probable cause
High side
Low side
1. Overcharged with refrigerant.
2. Non-condensable gases in refrigerant circuit (e.g. air)
3. Obstructed air-intake / discharge.
4. Hot air short circuiting in outdoor unit.
High side
Low side
High side
Low side
High side
Low side
High side
Low side
1. Air intake temperature of indoor unit too high.
1. Poor compression / no compression
(compressor defective)
2. Reversing valve leaking.
1. Undercharged with refrigerant.
2. Refrigerant leakage.
3. Air filter clogged / dirty (indoor unit).
4. Indoor fan locked / seized.
5. Defective defrost control, outdoor coil freeze up (heating).
6. Outdoor fan locked / seized (heating).
1. Outdoor fan blocked (cooling).
2. Outdoor coil dirty (cooling).
3. Indoor fan locked / seized (heating).
4. Indoor air filter clogged / dirty (heating).
5. Non-condensable gases in refrigerant circuit (e.g. air)
Diagnostic Guidelines
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