Short answer: When the AC does nothing at all, the cause is usually power or control, not refrigerant. Carrier’s checklist: confirm the thermostat is on Cool and calling for cooling, look for a tripped breaker or blown fuse, check the disconnect box by the outdoor unit, and replace a clogged filter. Many systems also have a condensate float switch that cuts power when the drain backs up. If a breaker trips again right after a reset, stop and call a pro.
Quick diagnosis
| What you notice | Most likely cause | What to check | Call a pro? |
|---|---|---|---|
| Nothing happens, thermostat blank | No power to the thermostat or system | Batteries, breaker, furnace switch | If still blank |
| Indoor fan runs, outdoor unit silent | Outdoor breaker, disconnect, capacitor or contactor | Check breaker and disconnect | Yes, for parts |
| Outdoor unit hums, fan does not spin | Failed capacitor or fan motor | Turn it off | Yes |
| System shut off, water near indoor unit | Condensate float switch tripped | Clear the drain line | If you cannot |
| Breaker trips right after reset | Electrical fault or failing compressor | Leave it off | Yes |
| Runs but blows no air at vents | Blower motor, frozen coil or very dirty filter | Check filter; look for ice | Often |
Check in this order
- Thermostat: set to Cool (or Auto), setpoint below room temperature, fan on Auto. Replace batteries; check a schedule is not overriding you.
- Breakers: the AC usually has its own breaker, sometimes two (indoor and outdoor). Reset a tripped one once.
- Outdoor disconnect: the gray box on the wall by the condenser must be on (some have a pull-out block or fuses).
- Furnace or air handler switch: the indoor unit has a light-switch-style power switch; make sure it is on.
- Filter: a badly clogged filter can freeze the coil and shut airflow down.
- Condensate: look for water in the drain pan or around the indoor unit. A tripped float switch cuts power until the drain is cleared.
Leave these to a technician
Carrier warns that capacitors, motors and compressors are high-voltage parts, and that refrigerant work requires certification. If you see ice, turn the system off to protect the compressor.
When to call a professional
- The breaker trips again after one reset.
- The outdoor unit hums, clicks or does not start while the thermostat calls for cooling.
- The blower does not run with a clean filter and power on.
- You see ice or suspect a refrigerant leak.
What it usually costs
HomeGuide (2026) puts most AC repairs at about $150 to $650. Typical prices: service call $75 to $200, capacitor $100 to $250, condenser fan motor $200 to $700, thermostat replacement $140 to $350, and clearing a condensate drain $75 to $250.
Frequently asked questions
Why is my AC not turning on but the thermostat is?
Check the AC breaker, the outdoor disconnect, the indoor unit switch and the condensate float switch. If all are on, a capacitor, contactor or control board may have failed.
Why does my AC turn on but not blow air?
A frozen coil, a very dirty filter or a failed blower motor are common causes.
Related problems
Sources
This guide is general information, not a substitute for an inspection by a licensed professional. See our disclaimer.