Air Conditioner Troubleshooting


Technicians usually have air conditioner troubleshooting guide in them after having gone through different kinds of problem in the field. Central air conditioning system usually have electronic control system that indicate the type of error or failure in the system.

Electronic controls are becoming more sophisticated and greatly help in troubleshooting of big system. There are electronic systems that can be remotely controlled or monitored and they are usually installed in mission critical type of environment.





Some of the possible causes of failure in the system are listed in the air conditioner troubleshooting guide below.

No Cooling Effect
Suction Frost
Low Pressure Switch Cuts-Off
High Pressure Switch Cuts-Off
High Pressure Side Too High
High Pressure Side Too Low
Low Pressure Side Too High
Low Pressure Side Too Low
Both Low Pressure and High Pressure Too High
Both Low Pressure and High Pressure Too Low
High Pressure Too Low and Low Pressure Too High


No Cooling Effect Air Conditioner Troubleshooting
  • Refrigerant is undercharged
  • Air conditioner unit is under capacity
  • Compressor valve damage or ineffective compression
  • Too much opening or inadequate opening of thermo valve
  • Ineffective contact of sensor bulb of thermo valve
  • Expansion valve not effective
  • Filter drier or strainer is clogged
  • Air filter is clogged
  • Evaporator coil is dirty
  • Fan coil motor is rotating in the reverse direction
  • Fan motor belt loose or slip
  • Temperature setting of thermostat too high
  • Expansion valve oversized or undersized
  • R.P.M of fan coil blower too low
  • Duct damper is closed
  • Duct resistance too high
  • Supply air short-circuit
Suction Frost Air Conditioner Troubleshooting
  • Air conditioner unit is over capacity
  • Air filter is clogged
  • Room temperature is too low
  • Evaporator coil is dirty
  • Fan coil motor is rotating in the reverse direction
  • Fan motor belt loose or slip
  • Temperature setting of thermostat too low
  • R.P.M of fan coil blower too low
  • Duct damper is closed
  • Duct resistance too high
  • Supply air short-circuit
  • Ambient temperature too low
Low Pressure Switch Cuts-Off Air Conditioner Troubleshooting
  • Fan coil motor is rotating in the reverse direction
  • Fan motor belt loose or slip
  • Temperature setting of thermostat too low
  • R.P.M of fan coil blower too low
  • Duct damper is closed
  • Duct resistance too high
  • Supply air short-circuit
  • Ambient temperature too low
  • Expansion valve undersized
  • Low pressure switch is not working
  • Refrigerant undercharge
  • Air conditioner unit is over capacity
  • Expansion valve clogged
  • Ineffective expansion valve
  • Air filter is clogged
  • Room temperature is too low
  • Evaporator coil is dirty
High Pressure Switch Cuts-Off
  • Overcharge of refrigerant
  • Air inside refrigerant circuit
  • Condenser water flow too little
  • Condenser inlet water temperature too high
  • Condenser is dirty
  • Air in condenser water flow
  • Refrigerant discharge valve blocked or closed
  • Condenser water circulating in the reverse direction
  • Condenser coil is very dirty
  • Condenser fan motor is not running
  • Condenser fan motor is rotating in the reverse direction
  • Poor air circulation of the condenser or air circulation blocked
  • High pressure switch not functioning
  • Condenser water pump malfunction
  • Cooling tower fan not running
  • Condenser water valves closed
  • Cooling tower fan rotates in the reverse direction
High Pressure Side Too High
  • Overcharge of refrigerant
  • Air inside refrigerant circuit
  • Condenser water flow too little
  • Condenser inlet water temperature too high
  • Condenser is dirty
  • Air in condenser water flow
  • Refrigerant discharge valve blocked or closed
  • Air conditioner unit is under capacity
  • Condenser water circulating in the reverse direction
  • Condenser coil is very dirty
  • Condenser fan motor is not running
  • Condenser fan motor is rotating in the reverse direction
  • Poor air circulation of the condenser or air circulation blocked
  • Condenser water pump malfunction
  • Cooling tower fan not running
  • Condenser water valves closed
  • Cooling tower fan rotates in the reverse direction
High Pressure Side Too Low
  • Refrigerant is undercharged
  • Excessive condenser water flow
  • Condenser outlet water temperature too low
  • Air conditioner unit is over capacity
  • Ineffective compression of compresor or valve is damaged
  • Ambient temperature too low
Low Pressure Side Too High
  • Refrigerant is overcharged
  • Expansion valve is oversized
  • Air conditioner unit is under capacity
  • Excessive opening of thermo valve
  • Ineffective compression of compresor or valve is damaged
  • Ineffective contact of sensor bulb of thermo valve
Low Pressure Side Too Low
  • Fan coil motor is rotating in the reverse direction
  • Fan motor belt loose or slip
  • Temperature setting of thermostat too low
  • R.P.M of fan coil blower too low
  • Duct damper is closed
  • Duct resistance too high
  • Supply air short-circuit
  • Expansion valve undersized
  • Refrigerant is undercharged
  • Air conditioner unit is over capacity
  • Not enough opening of thermo valve
  • Expansion valve clogged
  • Ineffective expansion valve
  • Air filter is clogged
  • Room temperature is too low
  • Evaporator coil is dirty
Both Low Pressure and High Pressure Too High
  • Condenser coil is very dirty
  • Condenser fan motor is not running
  • Condenser fan motor is rotating in the reverse direction
  • Poor air circulation of the condenser or air circulation blocked
  • Condenser water pump malfunction
  • Cooling tower fan not running
  • Condenser water valves closed
  • Cooling tower fan rotates in the reverse direction
  • Overcharge of refrigerant
  • Air inside refrigerant circuit
  • Condenser water flow too little
  • Condenser inlet water temperature too high
  • Condenser is dirty
  • Air in condenser water flow
  • Air conditioner unit is under capacity
  • Excessive opening of thermo valve
  • Ineffective contact of sensor bulb of thermo valve
  • Condenser water is circulating in the reverse direction
Both Low Pressure and High Pressure Too Low
  • Fan coil motor is rotating in the reverse direction
  • Fan motor belt loose or slip
  • Temperature setting of thermostat too low
  • R.P.M of fan coil blower too low
  • Duct damper is closed
  • Duct resistance too high
  • Supply air short-circuit
  • Expansion valve undersized
  • Refrigerant is undercharged
  • Air conditioner unit is over capacity
  • Not enough opening of thermo valve
  • Expansion valve clogged
  • Ineffective expansion valve
  • Air filter is clogged
  • Room temperature is too low
  • Evaporator coil is dirty
  • Ambient temperature too low
  • Excessive condenser water flow
  • Condenser outlet water temperature too low
  • Filter drier or strainer is clogged

High Pressure Too Low and Low Pressure Too High
  • Compressor valve damaged or ineffective compression







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