FAQ (Frequently Asked Questions)

This Q&A is not designed to replace the training required for a professional air conditioning/refrigeration service trademan. It is designed to point out guidelines and offer basic compressor and refrigeration/air conditioning knowledge.

Why is the compressor not starting (no humming noise)?
  1. System component are not functioning properly:
    • a. Control/contactor, of the starting relay, is stuck in open position.
    • b. System temperature controller is broken due to cold temperature.
    • c. Thermostat is not functioning properly.
  2. The system ON/OFF switch may be opened.
  3. The circuit breaker is tripped. OR Fuse is blowed or removed.
  4. Thermal protector is not functioning properly.
  5. Improperly or loose electrical wiring.
  6. The motor has a ground connection.
Why is the compressor not starting (there is a humming noise but trips on thermal protector)?
  1. Improperly or loose electrical wiring.
  2. There is a low voltage supply to compressor.
  3. System components, such as thermostat or control/contactor, may not be functioning properly.
  4. Compressor electrical problems:
    • a. Compressor motor has a short circuit.
    • b. Start capacitor not working properly.
    • c. Starting relay contacts do not close properly.
  5. Excessive liquid refrigerant is presence inside the compressor
  6. Mechanical components failure inside the compressor.
The compressor starts normally but does not switch from the start winding to run winding. Why?
  1. Improperly or loose electrical wiring.
  2. here is a low voltage supply to compressor.
  3. Compressor electrical problems:
    • a. Compressor motor has a short circuit.
    • b. Starting relay contacts remain closed.
    • c. Run capacitor is not working properly.
  4. The compressor discharge pressure is too high.
  5. IMechanical components failure inside the compressor.
The compressor starts and runs normally, but short cycles on thermal protector
  1. There is excessive current passing through thermal protector:
    • a. Extra source of current is drawn.
    • b. Compressor motor has winding shorted
  2. Low voltage to compressor (single phase) or unbalanced voltage (three phase).
  3. Compressor electrical problems, such as thermal protector or run capacitor are not working properly.
  4. The compressor discharge pressure is too high.
  5. The compressor suction pressure is too high.
  6. The compressor return gas is too warm.
Refrigeration/Air conditioning unit is running normally but the running cycle is shorter than normally due to other component (s) rather than thermal protector. Why is this occurring?
  1. System components, such as thermostat, temperature control or contactor, are not functioning properly.
  2. High pressure control cut-out due to:
    • a. Insufficient air or water supply.
    • b. Overcharge of refrigerant.
    • c. Air in system.
    • d. There is a water leak into the refrigerant side of a water-utilizing system.
  3. Low pressure cut-out due to:
    • a. The solenoid valve, in the liquid line, is leaking.
    • b. Undercharge of refrigerant.
    • c. Restriction in expansion device
Why does the refrigeration/air conditioning unit operates for too long?
  1. System components, such as thermostat or contactor, are not functioning properly. Control contacts may be closed.
  2. There is excessive load inside the unit.
  3. Poor insulation, or system inadequate to handle load.
  4. Evaporator coil iced.
  5. Restriction in refrigeration system.
  6. Dirty condenser coil.
  7. Filter is dirty
  8. Undercharge of refrigerant
What is causing the high temperature inside the refrigeration/air conditioning unit?
  1. System problems, such as:
    • a. temperature control setting too high
    • b. expansion valve too small
    • c. cooling coils too small
    • d. inadequate air circulation
  2. There is a water leak into the refrigerant side of a water- utilizing system.
Why is the suction line frosting or sweating?

System problems, such as:

  • a. expansion valve is passing excessive refrigerant
  • b. expansion valve is oversized
  • c. evaporator fan is not running
  • d. overcharge of refrigerant

Why is the liquid line frosting or sweating?

System problems such as, restriction in dehydrator or strainer or liquid shut-off (king valve) is partially closed.