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Problem
Probable Cause
Solution
Noisy Operation
Air noise
Check ductwork Air Velocity too high
Chattering contactor
Check for adequate control voltage, check
for shorts or breaks, check thermostat,
check contactor points
Tubing rattle
Dampen by taping or clamping, bend tubing
away from contact where possible
High Suction Pressure
Excessive load on evaporator coil
Check for high entering wet bulb
temperature Check for excessive airflow
Broken compressor valves Scroll
compressors do not have valves
Scroll compressors should not be pumped
down below 5 PSI
Compressor is unloaded
Recalibrate unloader pressure switch
Leaking check valve
Check temperature across check valve
Expansion valve not secured to suction line
or TXV defective
Check the TXV, ensure bulb is insulated
High Discharge
Pressure
TXV setting
Check TXV setting and calibrate superheat
Air inlet to condensing unit dirty
or obstructed
Check for proper clearances and possible
air recirculation
Condensing unit fan, motor defective
Check condensing unit fan motor and
run capacitor
Condensing unit fan control has
incorrect setting
Check calibration of low ambient head
pressure control
Suction Pressure
Too Low
Refrigerant undercharge
Check pressures and subcooling
Blower running backwards
Interchange any two wires connected
to motor
Defective or improperly adjusted
expansion valve
Check superheat and adjust TXV
Dirty filter
Check filter and evaporator coil
Too little airflow or low entering
air temperature
Check airflow and entering air wet
bulb conditions
Restriction in suction or liquid line
Check refrigerant circuit for restriction
Head Pressure
Too Low
Insufficient refrigerant charge
Check subcooling, check for leak
Defective or improperly adjusted
expansion valve
Check superheat and adjust TXV
Low suction pressure
See above – suction pressure too low
Condensing unit fan control setting
Check calibration of low ambient control
Compressor defective
See above – high suction pressure
Liquid Line Too Hot
Refrigerant undercharged
See above – high discharge pressure
High discharge pressure
Restriction upstream at point of frosting
Suction Line Frosting
Insufficient evaporator airflow
Check airflow, check fan VFD,
closed dampers
Restriction in suction or liquid line
Restriction upstream at point of frosting
Malfunctioning or defective expansion valve Check bulb of TXV
Table 14.3: Refrigeration Circuit
RC/FC Series Installation, Operation, and Maintenance Manual
