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REFRIGERATION

Troubleshooting

Compressor not starting, or clicking on and off

A compressor that tries to start, clicks, hums for a second and goes quiet is usually being shut off by its own overload protector. That protector is doing its job: something is stopping the motor from starting, and it trips before the windings burn. The common reasons in India are low supply voltage during peak hours, a tired start relay or capacitor, a hot condenser that keeps pressures high, or a restart attempted too soon after a power cut. Repeated start attempts heat the motor, so do not keep switching the unit on and off hoping it will catch.

First, check these

  1. Listen and time it. A click, a short hum, then silence and another click a few minutes later is the overload cycling. Note the pattern for the technician.
  2. Check the controller. Many controllers have a restart delay of a few minutes after power returns or after the compressor stops. Wait it out before deciding there is a fault.
  3. If you have a stabiliser or voltage protector with a display, read the incoming voltage. Starting is hardest when supply sags well below 230 V in the evening peak.
  4. Make sure the condenser is clean and the condenser fan turns when the unit calls for cooling.
  5. Check that the plug, socket and extension board are not warm, loose or scorched. Undersized extension leads drop voltage at start.

Likely causes

  1. 1. Low or unstable supply voltage

    Technician job

    Signs: Problem worst in the evening or summer peak, lights dim when the compressor tries to start, other appliances on the same line.

    Fix: Plug directly into a properly rated socket on its own circuit, avoid extension boards, and use a stabiliser or voltage protector sized for the compressor's starting current. An electrician should check the supply if voltage is regularly low.

  2. 2. Restart attempted against high pressure

    You can check this

    Signs: Happens right after a power cut, a quick off-on, or switching between stabiliser and mains.

    Fix: Leave the unit off for a few minutes so pressures equalise, then restart once. A voltage protector with a built-in time delay prevents this automatically.

  3. 3. Dirty condenser or failed condenser fan

    You can check this

    Signs: Compressor body very hot, the overload trips after a short run, hot air trapped around the unit.

    Fix: Isolate power and clean the condenser. If the condenser fan is not spinning, call a technician to replace it.

  4. 4. Faulty start relay, PTC starter or capacitor

    Technician job

    Signs: Compressor hums briefly but never runs, clicking from the compressor terminal box, sometimes after a voltage spike.

    Fix: A technician tests and replaces the starting components. These are inexpensive parts but sit at mains voltage inside the terminal box.

  5. 5. Controller or thermostat not calling for cooling

    Technician job

    Signs: No click at all, display blank or showing an alarm, fans may run but the compressor never tries.

    Fix: Check that the setpoint is sensible and the unit is not in defrost or standby. Beyond that, a technician should test the controller output and wiring.

  6. 6. Compressor motor or mechanical failure

    Technician job

    Signs: Starting parts are good and voltage is fine but the compressor still will not run, or the MCB trips when it tries.

    Fix: A technician confirms with winding and insulation tests. Replacement is a sealed-system job that includes evacuation and recharging.

When to call a technician

Call a technician if the compressor has not run after one clean restart with a wait of several minutes, if the clicking continues for more than one or two cycles, if the MCB or RCCB trips, or if you smell burning. Every failed start heats the windings; leaving it clicking for hours can turn a cheap relay fix into a compressor replacement. Switch it off and move stock while you wait.

The terminal box on the compressor carries mains voltage and may hold a charged capacitor, so staff should never open it. Isolate power before cleaning. Units using hydrocarbon refrigerant (R290 or R600a) must only be repaired by trained technicians with suitable tools and no ignition sources nearby.

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