Your AC works hard — especially in peak summer — and when it starts acting strange, the culprit is often a single cylindrical component you’ve probably never thought about: the dual run capacitor.

Here are the 5 signs it may be failing:

1. The unit hums but doesn’t start. The capacitor stores the energy needed to kick-start your compressor and fan motor. When it weakens, motors struggle to turn over, producing that familiar low hum with no airflow.

2. The fan runs but the compressor doesn’t (or vice versa). A dual run capacitor has two separate circuits — one for the HERM (compressor) terminal and one for the FAN terminal. A partial failure can knock out just one side, leaving half your system dead.

3. Higher-than-normal energy bills. When a capacitor begins to fail, compressors and fan motors struggle to achieve desired temperatures, leading to longer run times and higher energy bills. One Products

4. Frequent short-cycling. The system turning on and off more than usual is a classic sign the capacitor can’t sustain a full cooling cycle.

5. A visibly bulging or leaking casing. Heat and age cause the capacitor’s internals to expand. If the top is domed or you see oily residue, it needs immediate replacement.

What to do: When buying a replacement, capacitance must match exactly (e.g. 40+5 µF), the voltage rating must match or exceed the original, and the terminal type on dual run capacitors should have 3 terminals: C / FAN / HERM. When in doubt, bring the old unit to a precision capacitor supplier who can cross-reference the specs for you. Ersa Electronics