McQuay MWM - General Troubleshooting by Pressure Readings

MCQUAY Service Guide Book Diagnosis
76
7.5 General Troubleshooting Guide
By means of pressure readings:
Pressure Probable Cause
Too Low
A Little Low
Normal
A Little
High
Too High
High Side
Low Side
1. Overcharged with refrigerant.
2. Non-condensable gases in refrigerant
circuit (eg. Oil)
3. Obstructed air-intake / discharge.
4. Short circuit of hot air at condensing unit.
High Side
Low Side
1. Poor compression / no compression
(compressor defective).
2. Check valve stick in open position.
3. Reversing valve leaking (for heatpump
only).
High Side
Low Side
1. Undercharged with refrigerant.
2. Refrigerant leakage.
3. Air filter clogged / dirty (indoor unit).
4. Indoor fan locked (cooling).
5. Defective defrosts control, outdoor coil
freeze up (heating).
6. Outdoor fan locked (heating).
High Side
Low Side
1. Outdoor fan blocked (cooling).
2. Outdoor coil dirty (cooling).
3. Indoor fan locked (heating).
4. Indoor filter clogged dirty (heating).
High Side
Low Side
1. Air intake temperature of indoor unit too
high.
Data
Circuit