If your AC won't start, hums but doesn't kick on, or shuts off randomly, there's a good chance the culprit is a small, inexpensive part called the capacitor. It's one of the most common AC failures we see across the northwest suburbs — and one of the most fixable.
What the capacitor does
The capacitor stores and delivers the jolt of energy that starts your AC's motors — the compressor and fan. Heat is its enemy, and after a string of hot Illinois summers, capacitors wear out. When one fails, the motors can't start properly.
Signs of a bad capacitor
- AC won't turn on at all
- You hear a humming or buzzing but it won't start (see our AC noises guide)
- The outdoor fan won't spin, or only spins if you nudge it
- The AC shuts off on its own (short cycling)
- It takes several tries to start, or starts slowly
- A visibly swollen, bulging, or leaking capacitor
What does replacement cost?
Capacitors are one of the more affordable AC repairs — a modest part plus labor. Exact pricing depends on your system, which is why we give you an upfront price after diagnosing it (more in our AC repair cost guide). Catching a bad capacitor early can prevent damage to the far pricier compressor.
Why it's not a safe DIY fix
We get it — videos make it look easy. But a capacitor stores a powerful electrical charge even when the power is off, and discharging it incorrectly can cause a serious shock. Installing the wrong rating can also damage your compressor. This is a quick, low-cost job for a trained tech — not worth the risk.
Get it fixed fast
A failed capacitor usually means a same-day fix. Thermo Master provides fast, affordable AC repair across Palatine and the NW suburbs. Reach out and we'll have you cool again quickly.