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Problem
Too cool and then too warm
Not cool enough on warm days
Certain areas too cool, others too
warm
Compressor is noisy
System runs—blows cold air during
heating
Unit will not terminate defrost
Unit will not defrost
System Operating Pressures
Low suction pressure
14
Cause/Test Method and/or Solution
Faulty thermostat. Test continuity of thermostat and wiring. Replace, if needed.
Improper cooling anticipator. Check resistance of anticipator.
Improperly located thermostat. Relocate thermostat.
Airflow unbalanced. Readjust air volume dampers.
Dirty air filter. Inspect filter. Clean or replace, if needed.
Dirty indoor coil. Inspect coil. Clean, if needed.
Not enough air across indoor coil. Speed blower. Check duct static pressure.
Dirty outdoor coil. Inspect coil. Clean, if needed.
Noncondensibles. Recover charge. Evacuate and recharge.
Recirculation of condensing air. Remove obstruction to airflow.
Infiltration of outdoor air. Check windows, doors, vent fans, etc.
System undersized. Refigure cooling load.
Wrong type of expansion valve. Replace valve.
Expansion valve restricted. Replace valve.
Undersized expansion valve. Replace valve.
Dirty air filter. Inspect filter. Clean or replace, if needed.
Dirty indoor coil. Inspect coil. Clean, if needed.
Not enough air across indoor coil. Speed blower. Check duct static pressure.
Infiltration of outdoor air. Check windows, doors, vent fans, etc.
Airflow unbalanced. Readjust air volume dampers.
Overcharge of refrigerant. Recover part of charge.
Broken internal parts. Replace compressor.
Broken valves. Test compressor efficiency. Replace if needed.
Expansion valve bulb loose. Tighten bulb bracket.
Loose hold-down bolts. Tighten bolts.
Internal compressor overload open. Test continuity of overload.
Compressor stuck. Use test cord. Replace, if needed.
Shortage of refrigerant. Test for leaks. Add refrigerant.
Open element or limit on electric heater. Test heater element and controls.
Overcharge of refrigerant. Recover part of charge.
Noncondensibles. Recover charge. Evacuate and recharge.
Broken internal parts. Replace compressor.
Inefficient compressor. Test compressor efficiency.
Faulty reversing valve. Replace valve or solenoid.
Faulty defrost control. Test control. Replace if needed.
Faulty defrost thermostat. Test defrost thermostat. Replace if needed.
Faulty reversing valve. Replace valve or solenoid.
Faulty defrost control. Test control. Replace if needed.
Faulty defrost thermostat. Test defrost thermostat. Replace if needed.
Faulty reversing valve. Replace valve or solenoid.
Faulty defrost control. Test control. Replace if needed.
Faulty defrost thermostat. Test defrost thermostat. Replace if needed.
Faulty evaporator fan motor. Repair or replace.
Shortage of refrigerant. Test for leaks. Add refrigerant.
Restricted liquid line. Replace restricted part.
Dirty air filter. Inspect filter. Clean or replace, if needed.
Dirty indoor coil. Inspect coil. Clean, if needed.
Not enough air across indoor coil. Speed blower. Check duct static pressure.
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