IM 861
25
Figure 19: Cooling Trouble Shooting Chart
SYMPTOM POSSIBLE CAUSE REMEDY
Unit will not run • Power off or loose electrical connection • Check for correct voltage at compressor contactor in control
box
• Thermostat out of calibration-set too high • Reset
• Failed contactor • Check for 24 volts at contactor coil - replace if contacts are
open
• Blown fuses • Replace fuses
• Transformer defective • Check wiring-replace transformer
• High pressure control open (if provided) • Reset-also see high head pressure remedy-The high pressure
control opens at 450 PSIG
• Interconnecting low voltage wiring damaged • Replace thermostat wiring
Condenser fan runs, compressor • Loose connection • Check for correct voltage at compressor -
doesn’t check & tighten all connections
• Compressor stuck, grounded or open motor winding • Wait at least 2 hours for overload to reset.
open internal overload. If still open, replace the compressor.
• Low voltage condition At compressor terminals, voltage must be within 10% of rating
plate volts when unit is operating.
Insufficient cooling • Improperly sized unit • Recalculate load
• Improper airflow • Check - should be approximately 400 CFM per ton.
• Incorrect refrigerant charge • Charge per procedure attached to unit service panel.
• Air, non-condensibles or moisture in system • Recover refrigerant, evacuate & recharge, add filter drier
• Incorrect voltage • At compressor terminals, voltage must be within 10% of rating
plate volts when unit is operating.
Compressor short cycles • Incorrect voltage • At compressor terminals, voltage must be ± 10% of
nameplate marking when unit is operating.
• Defective overload protector • Replace - check for correct voltage
• Refrigerant undercharge • Add refrigerant
Registers sweat • Low evaporator airflow • Increase speed of blower or reduce restriction - replace air
filter
High head-low vapor pressures • Restriction in liquid line, expansion device or filter drier • Remove or replace defective component
• Incorrect capillary tubes • Change coil assembly
High head-high or normal vapor • Dirty condenser coil • Clean coil
pressure - Cooling mode • Refrigerant overcharge • Correct system charge
• Condenser fan not running • Repair or replace
• Air or non-condensibles in system • Recover refrigerant, evacuate & recharge
Low head-high vapor pressures • Defective Compressor valves • Replace compressor
• Incorrect capillary tubes • Replace coil assembly
Low vapor - cool compressor - • Low evaporator airflow • Increase speed of blower or reduce restriction - replace air
iced evaporator coil filter
• Operating below 65°F outdoors • Add Low Ambient Kit
• Moisture in system • Recover refrigerant - evacuate & recharge - add filter drier
High vapor pressure • Excessive load • Recheck load calculation
• Defective compressor • Replace
Fluctuating head & vapor • Air or non-condensibles in system • Recover refrigerant, evacuate & recharge
pressures
Gurgle or pulsing noise at • Air or non-condensibles in system • Recover refrigerant, evacuate & recharge
expansion device or liquid line
Circulating air blower & inducer • Manual reset overtemperature control • Reset or replace
run continuously, tripped
compressor will not start • Wire loose in limit circuit • Check wiring
Disconnect all power to unit before servicing. Contactor may break only one side. Failure to shut off power can cause electrical
shock resulting in personal injury or death.
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DANGER
!
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