A 60/5 capacitor reads 30/5, but the AC still runs. How?
A capacitor is not a switch: it does not simply work or not work, it helps the motor. 60/5 is two capacitors in one can: 60 µF for the compressor (HERM terminal) and 5 µF for the fan (FAN). With 30 left instead of 60 on HERM, the compressor can still start and run, especially in mild weather with equalized pressures. But it runs with weak torque and below design efficiency, and amps and winding heat can go up. On a hot day or a quick restart it will stop starting or trip on overload. The rule is within the tolerance printed on the can (usually ±5 or ±6 %). 30 out of 60 is 50 % low: replace it now, do not wait for the compressor to fail.
Likely causes, in order
1. How to test a capacitor: with a meter and under load (amps × 2652 ÷ volts)
Tools: Multimeter with µF mode (or capacitor tester), 20 kΩ 5 W resistor on insulated leads (discharge tool)
- KILL POWER at the disconnect. Remove the electrical panel.
- Inspect: a cylinder with 3 terminals (C, HERM, FAN) or two 2-terminal ones. Bulged top, leaking, rust — replace on sight.
- Discharge: with a 20 kΩ 5 W resistor on insulated leads (or a discharge tool) bridge C to HERM and C to FAN. Then confirm 0 V with the meter. Don't dead-short it with a screwdriver — arc, burns, damaged terminals.
- Photograph the wires before pulling them. The rating is on the side: e.g. 45/5 µF 440V (45 — compressor, 5 — fan).
- Meter in µF mode. Measure C–HERM and C–FAN. Normal: within the tolerance on the label, usually ±6 %. For 45 µF that's 42.3–47.7. For 5 µF — 4.7–5.3.
- Replace with the same µF and equal or higher voltage (440 V can replace 370). Wires: C — to the contactor, HERM — compressor, FAN — fan motor.
2. Replacement: discharge it, match the µF, same or higher voltage, check the contactor
Tools: µF meter, insulated screwdriver
- Kill power and verify it's dead with a meter. Discharge the capacitor through a 20 kΩ 5 W resistor on insulated leads (C–HERM, then C–FAN), not by shorting with a screwdriver. Confirm 0 V on the terminals.
- Inspect: bulged top, leak — replace on sight. Measure µF on C–HERM and C–FAN: within the tolerance on the label (usually ±6 %).
- Contactor: contacts not burnt, not stuck, 24 V at the coil on a call, 240 V out equal to in.
- Tighten all terminals, replace burnt spades.
- This is done BEFORE any top-off: a weak capacitor raises compressor amps and heat, makes starting hard, and spoils every reading.