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FREQUENTLY ASKED QUESTIONS

[ FAQ ]

FREQUENTLY ASKED QUESTIONS

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

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:
    • The compressor motor has a short circuit.
    • The start capacitor not working properly.
    • Starting relay contacts do not close properly.
  5. The excessive liquid refrigerant is present 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 the compressor.
  3. Compressor electrical problems:
    • The compressor motor has a short circuit.
    • Starting relay contacts remain closed.
    • Run capacitor is not working properly.
  4. The compressor discharge pressure is too high.
  5. mechanical 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:
      • An extra source of current is drawn.
      • The compressor motor has winding shorted
    2. Low voltage to the 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 thermostats, temperature control, or contactor, are not functioning properly.
    2. High-pressure control cut-out due to:
      • Insufficient air or water supply.
      • Overcharge of refrigerant.
      • Air in system.
      • There is a water leak into the refrigerant side of a water-utilizing system.
    3. Low-pressure cut-out due to:
      • The solenoid valve, in the liquid line, is leaking.
      • Undercharge of refrigerant.
      • Restriction in the expansion device
Why does the refrigeration/air conditioning unit operates for too long?
    1. System components, such as the 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 the load.
    4. Evaporator coil iced.
    5. Restriction in the 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:
      • temperature control set too high
      • expansion valve too small
      • cooling coils too small
      • inadequate air circulation
    2. There is a water leak into the refrigerant side of water- utilizing the system
Why is the suction line frosting or sweating?

    1. System problems, such as:

      • a. expansion valve is passing excessive refrigerant
      • b. the expansion valve is oversized
      • c. evaporator fan is not running
      • d. overcharge of refrigerant
Why is the liquid line frosting or sweating?
  1. System problems such as restriction in dehydrator or strainer or liquid shut-off (king valve) are partially closed.