If your AC outdoor unit hums but the compressor or fan wont start, a failed capacitor is the most likely cause. This guide walks you through diagnosing and replacing one safely.
Visual inspection first
Before pulling out a multimeter, look for these obvious signs of a dead capacitor:
- Bulged top: A capacitor with a domed or swollen top is finished — replace it.
- Oil leak: Brown residue around the base indicates the dielectric has failed.
- Burn marks: Discoloration on the terminals or case is a clear failure signal.
Discharge before handling
Even disconnected, capacitors store charge. Short the terminals through a 20kΩ resistor (or use an insulated screwdriver across the terminals briefly) before touching them.
Multimeter test
Switch your multimeter to capacitance (μF) mode. Connect the leads to the capacitor terminals and read the value. Compare it against the rating printed on the side — most capacitors should be within ±5% of the printed value. Anything more than 10% off, replace it.
Picking the right replacement
Match the microfarad rating AND the voltage rating exactly. A 35 μF / 450V capacitor cannot be replaced with a 35 μF / 250V part. If in doubt, photograph the old one and message us on WhatsApp — well confirm the correct SKU.