Told to replace unit, capacitor fix restored cooling
Aircon case in Sengkang, Singapore: electrical/control traced to run capacitor degraded significantly below rated value — outdoor unit could not start after targeted diagnosis checks.
Case details
What client reported
The customer said the outdoor unit had stopped starting about three weeks earlier. A contractor had come out, spent a few minutes looking, and told them the unit was 10 years old and not worth fixing. They should replace the whole system. The customer wanted a second check before committing to replacement.
What we found
We started at the cheapest and most likely cause for a non-starting outdoor unit on a 10-year-old unit — the run capacitor
- Run capacitor measured — reading was 7.2 µF against a rated value of 15 µF, a 52% drop from specification
- Contactor tested — contacts clean, coil energising correctly, no fault
- Compressor winding resistance checked across all three terminals — all readings within normal range, no open or short circuit
- New capacitor of correct rating fitted — outdoor unit started on the first attempt and ran through a full cooling cycle
The run capacitor had degraded to approximately half its rated capacitance. Below a certain threshold, it can no longer provide enough starting torque for the compressor motor. The motor attempts to start, draws high current briefly, then either trips the thermal overload or stalls. The compressor motor itself was completely intact.
What we did
The degraded capacitor was replaced with the correct-rated component. The outdoor unit started immediately after the swap. We ran the system through a full cooling cycle and measured supply current at steady state. The readings were within the normal range for the model. The unit was cooling to the set temperature within the expected time.
Full operation was restored with a single component replacement. The customer was given a clear account of what was measured and what was replaced. This gave them documentation for future reference. The unit required no further work.
Timeline
Day 1
Outdoor unit not starting — previous contractor advised full unit replacement
Day 1
Capacitor measured at less than 60% of rated microfarad value — replaced with correct-rated component, outdoor unit started immediately
Day 1
Capacitor measured at less than 60% of rated value, replaced with correct component, outdoor unit started and cooling confirmed normal
What we learned
Why age alone doesn't justify unit replacement.
- A 10-year-old unit with no compressor wear or refrigerant faults can still have several years of useful life remaining. Good maintenance makes a significant difference.
- Capacitors degrade predictably over time as the internal dielectric material breaks down. This is a known consumable that typically needs replacement every 5 to 10 years.
- A degraded capacitor stops the compressor or fan motor from starting. The symptoms look like a dead outdoor unit, but the compressor itself may be completely intact.
- Recommending full replacement without measuring capacitor value is not proper diagnosis. The capacitor test takes under two minutes and either confirms or rules out the cheapest possible fix.
Common questions
Same situation with your aircon?
Describe what's happening. We'll work out the likely cause and tell you the right next step.
Describe it on WhatsApp