Form O-Y, PN 273647R5, Page 44
General Refrigeration Circuit (cont'd)
SYMPTOM
POSSIBLE CAUSE
REMEDY
F. Noisy unit
operation.
1. Blower rotational noise.
1. Check blower, motor and drive for faulty adjustment or noisy
bearings, loose parts, and/or blower out of balance.
2. Air noise.
2. Check duct work. Air velocity too high.
3. Chattering contactor.
3. Check for adequate control voltage; check for shorts or breaks;
check contact points.
4. Tubing rattle.
4. Dampen by taping or clamping, carefully bend tubing away from
contact when possible.
G. High suction
pressure.
1. Excessive load on evaporator coil.
1. Check superheat (Paragraph 3.6). Check for high entering wet
bulb temperature. Check for excessive air.
2. Compressor is unloaded.
2. Check head pressure. Check thermal expansion valve. If valve is
not functioning properly, check pressure drop across filter drier.
3. Expansion valve bulb not secured to
suction line or valve defective.
3. Check the thermal expansion valve; ensure bulb is attached
properly and insulated
H. High
discharge
pressure.
1. Refrigerant overcharge
1. Check subcooling. (Paragraph 3.6) Adjust refrigerant charge.
2. Thermal expansion valve setting
2. Check superheat and adjust valve as needed
.
2. Air inlet to condenser dirty or obstructed.
3. Check for proper clearances and possible air recirculating.
4. Condenser fan motor defective.
4. Check condenser fan motor(s).
I. Suction
pressure is too
low.
1. Refrigerant undercharge.
1. Check subcooling. (Paragraph 3.6) Add refrigerant as needed.
2. Thermal expansion valve setting
2. Check superheat and adjust valve as needed.
3. Blower running backward.
3. Interchange any two wires from 3 phase disconnect.
4. Loose blower, pulley, or belts.
4. Check drive pulley alignment and belt tension.
5. Dirty filter.
5. Check filter and evaporator coil.
6. Too little air flow or low entering air
temperature.
6. Check airflow and entering air wet bulb conditions.
7. Restriction in suction or liquid line.
7. Check refrigerant circuit for restriction.
J. Head
Pressure too
low.
1. Insufficient refrigerant charge.
1. Check subcooling (Paragraph 3.6). Check for leak. Repair and
add refrigerant.
2. Defective or improperly adjusted
expansion valve.
2. Check superheat (Paragraph 3.6) and adjust thermal expansion
valve.
3. Low suction pressure.
3. See “I. Suction pressure too low” above.
4. Defective compressor.
4. See "G. High suction pressure” above.
K. Compressor
short cycles..
1. Improper refrigerant charge.
1. Check subcooling and superheat. (Paragraph 3.6)
2. Defective high or low pressure control.
2. Check high or low pressure switch.
3. Liquid flood back.
3. Possible tight bearings, see above.
4. Defective expansion valve.
4. Check superheat and thermal expansion valve.
5. Poor air distribution.
5. Check duct work for recirculating.
6. High discharge pressure.
6. See “H. High discharge pressure” above.
7. Leaking discharge valves in compressor.
7. See “G. High suction pressure” above.
L. Running
cycle is too
long or unit
operates
continuously..
1. Refrigeration undercharged.
1. Check subcooling (Paragraph 3.6) and add refrigerant.
2. Dirty filter or evaporator coil.
2. Check filter, coil, and airflow. Clean and/or replace.
3. Dirty or clogged condenser coil.
3. Check coil and airflow. Clean.
4. Air or other non-condensables in system.
4. Check equalized high side pressure with equivalent outdoor
temperature.
5. Defective compressor.
5. See “G. High suction pressure” above.
6. Restriction in suction and liquid line.
6. Check for restrictions in refrigerant circuit.
7. Control contacts stuck.
7. Check wiring.
M. Supply air
temperature is
too high.
1. Refrigerant undercharge or leak in
system.
1. Check subcooling
(Paragraph 3.6). Check for leak. Repair and
add refrigerant.
2. Evaporator plugged with dirt or ice.
2. Check evaporator, airflow, and filter. Clean.
3. Improperly adjusted or defective
expansion valve.
3. Check superheat (Paragraph 3.6) and adjust thermal expansion
valve. Check expansion valve bulb placement and insulation.
4. Defective compressor.
4. Check compressor for proper operation.
5. High discharge pressure.
5. See “H. High discharge pressure” above.
6. Airflow is too high.
6. Check external static pressure.
N. Supply air
temperature is
too low.
1. Airflow is too low.
1. Check evaporator coil; check filters; check for closed dampers or
grills; check drive for loose parts, belts, or misalignment; and check
external static pressure.
2. Return air temperature too low.
2. Check entering air wet bulb conditions.
O. Liquid line
is too hot.
1. Refrigerant undercharge.
1. Check subcooling.
2. High discharge pressure.
2. See H. above.
7.0 Troubleshooting (cont'd)
7.1 Troubleshooting - Refrigeration (cont'd)
