Your AC won’t turn on in Phoenix summer — one of the most stressful home emergencies in the Valley. Before calling a technician, run through this diagnostic checklist. Half the time, the fix is something you can handle in 5 minutes.
5-Minute Checks Before You Call
1. Check the thermostat. Replace batteries if it’s battery-powered. Make sure it’s set to COOL and the temperature is at least 3°F below the current room temperature. If you recently changed the thermostat settings, wait 5 minutes — most systems have a built-in delay (3–5 minutes) to protect the compressor.
2. Check the circuit breaker. Find the breaker labeled “AC,” “Air Conditioner,” or “HVAC” in your electrical panel. If it’s tripped (in the middle position), switch it fully OFF then back ON. If it trips again immediately, stop — you have an electrical fault requiring a technician.
3. Check the disconnect box. The metal box near your outdoor condenser unit has a disconnect switch. Make sure it’s in the ON position. It can be accidentally bumped to OFF.
4. Check the air filter. A severely clogged filter causes the air handler to overheat and trip an internal safety switch. Replace the filter and reset the switch (usually a red button on the air handler).
5. Check the condensate drain pan. Many air handlers have a float switch that shuts the system down when the drain pan is full of water. If your unit is in the attic or closet, look for standing water in the pan. Clear the drain line (pour distilled vinegar down the access port) and reset the float switch.
| Symptom | Most Likely Cause | Action |
|---|---|---|
| Nothing happens at all | No power — breaker, disconnect, or blown fuse | Check breaker and disconnect first |
| Thermostat works, nothing outside | Tripped breaker, bad capacitor, failed contactor | Check breaker; call tech if breaker is fine |
| Fan runs, compressor doesn’t | Bad start capacitor (very common in Phoenix) | Call tech — capacitor replacement |
| Unit starts then shuts off in 1–2 min | High-pressure lockout — dirty coils, low refrigerant | Rinse condenser; call if repeats |
| Thermostat blank/unresponsive | Dead batteries or no 24V power from air handler | Replace batteries; check air handler breaker |
When to Call Immediately
Stop DIY troubleshooting and call a technician if: the breaker trips again after resetting, you hear buzzing or humming at the outdoor unit (stuck compressor or failed capacitor), you smell burning from vents or the outdoor unit, or you see sparks or burn marks at the disconnect box. These indicate electrical faults requiring licensed hands.
Discount AC & Refrigeration handles no-start and no-cooling calls across Phoenix, Gilbert, Scottsdale, Peoria, and Surprise. Call 480 478-2616 — available 6 AM–midnight, 7 days a week. See our Phoenix AC repair page for details.
Frequently Asked Questions
Answered by Discount AC & Refrigeration — EPA Certified · ROC #361623 · Phoenix, AZ
