42
Table 14 — Refrigeration Circuit
PROBLEM
POSSIBLE 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 condenser dirty or obstructed
Check for proper clearances and possible air recir-
culation.
Condenser fan, motor defective
Check condenser fan motor and run capacitor.
Condenser fan control has incorrect setting
Check calibration of low ambient head pressure con-
trol.
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.
Condenser fan control setting
Check calibration of low ambient control.
Defective compressor
See above –
high suction pressure
.
Compressor short cycles
Thermostat location or malfunction
Check thermostat. Check heat anticipator setting.
Improper refrigerant charge
Check subcooling. Verify superheat.
Defective high or low pressure control
Check high or low pressure switch.
Cycling on internal overload
Possible tight bearings – see above.
Defective expansion valve
Check TXV and superheat.
Poor air distribution
Check ductwork for recirculation.
High discharge pressure
See above –
high discharge pressure
.
Leaking discharge valves in compressor
See above –
high suction pressure
.
Running cycle too long or
unit operates continuously
Refrigerant undercharged
Check subcooling.
Dirty filter or evaporator coil
Check filter, coil and airflow.
Dirty or clogged condenser coil
Check coil and airflow.
Air or other non-condensables in system
Check equalized high side pressure with equivalent
outdoor temperature.
Defective compressor
See above –
high suction pressure
.
Restriction in suction and liquid line
Check for restrictions in refrigerant circuit.
Control contacts stuck
Check thermostat, shorts in wiring, slave relay com-
pressor contactor.
Supply air temperature too
high
Refrigerant undercharge or leak in system
Check subcooling and check for leaks.
Evaporator plugged with dirt or ice
Check evaporator, airflow, and filter.
Improperly adjusted or defective expansion valve
Check superheat and adjust TXV. Check bulb.
Defective compressor
Check compressor for proper operation.
High discharge pressure
See above-
high discharge pressure
.
Airflow is too high
Check external static pressure.
Supply air temperature too low
Airflow is too low
Check evaporator coil, filter. Check for closed damp-
ers, grills, drive for loose parts, belts, misalignment.
Check external static pressure.
Return air temperature too low
Check entering air wet bulb conditions.
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.
Blower motor not running
Improper wiring
Check wiring diagram.
Defective motor
Check motor controller.
Defective thermostat or control circuit
Check “R” and “G” circuit.
Motor off on overload protector
Allow motor to cool. Check amperage.
