AC Not Turning On in Chicago? Here's How to Diagnose It

Common causes of ac not turning on

1. Tripped breaker or blown fuse

The most common cause. A breaker that has tripped once may simply have been a surge, but a breaker that trips again immediately is protecting the circuit from a real fault — a shorted compressor, a failing capacitor, or damaged wiring. Repeated resets on a breaker that keeps tripping risk damage to the equipment, so tell us if it has tripped more than once.

2. Thermostat issue

Dead batteries, wrong mode setting, or a failed thermostat. Replace batteries first. Set mode to 'Cool' and target 5° below room temperature. Listen for a click from the indoor air handler when the thermostat triggers.

3. Condensate float switch tripped

High-efficiency AC systems have a float switch in the condensate drain that shuts the unit off if the drain backs up. This protects your ceiling from water damage. The switch is doing its job — the blocked drain behind it is the actual fault, and clearing it properly is part of the repair.

4. Failed capacitor

The capacitor stores the electrical charge that starts the compressor and fan. If it fails, you may hear a humming sound from the outdoor unit but nothing starts.

5. Bad contactor

The contactor is a relay that switches power to the outdoor unit. When it fails (often from heat or aging), the outdoor unit stays off even when the thermostat calls for cooling.

6. Control board failure

If everything else checks out, the indoor unit's control board may have failed. This requires diagnosis — boards are model-specific.

What to tell us when you call

The more you can describe, the better the chance we arrive with the right part already on the truck. It helps to know:

1. Does anything happen at all — any hum, click, or fan movement?
2. Is the thermostat display lit, and is it set to Cool?
3. Is there standing water in the condensate drain pan?
4. Has the system been shutting off intermittently before this?
5. How old is the system, and when was it last serviced?

When to call SAVA

If the system won't start — or if the breaker has tripped more than once — call us and leave it off in the meantime. Repeatedly resetting a breaker that keeps tripping can damage components or cause an electrical fire.

SAVA is a family-owned, EPA Section 608 Certified HVAC company serving Chicago and North Shore suburbs. We diagnose the exact fault before any work begins, carry common parts for same-day repairs, and give honest repair-versus-replace guidance. Learn more about our AC repair service or emergency AC repair.

Brands we service

Plus most other residential central AC brands — if yours isn't on the list, call and we'll confirm.

Frequently Asked Questions