A Tucson AC that runs almost nonstop on a 100F afternoon is often doing its job. An AC that runs nonstop and still can’t hold the thermostat setting on a milder day has a problem. Climate Pros Tucson matches you with a licensed local pro when it’s the second kind.
Is long runtime normal in Tucson?
Yes, on the hottest days. Tucson averages about 68 days a year with a high at or above 100F, per the 1991-2020 normals at Tucson International Airport, and 2024 set a record with 112 such days. The City of Tucson’s energy code sets a summer design temperature of 105F, and that’s the figure a load calculation sizes the system against.
On a day hotter than the design number, the system may run continuously. That’s not a fault. The clue is whether the house stays near the setpoint while it runs.
What does a real problem look like?
Constant running plus any of these points to a fault:
- Air from the vents feels warm or only slightly cool.
- The house sits several degrees above the setpoint on a day in the 80s or low 90s.
- Ice or frost shows on the copper line or the indoor coil.
- The outdoor unit runs while the thermostat says the house is cool.
- Humidity inside feels high, especially in July and August when dew points climb into the high 50s.
What causes the common faults?
Dirty filter or blocked coil. Weak airflow makes the system run longer for less cooling. A clogged filter is the easiest check. Dust storms during the monsoon season can load a filter fast.
Low refrigerant. Refrigerant doesn’t get used up. Low charge means a leak, and a top-up without a leak repair only buys time. Only technicians who hold EPA Section 608 certification may handle refrigerant. Our refrigerant leak signs guide has the details.
Dirty condenser coil. Dust and windblown debris coat the outdoor coil, and the unit can’t shed heat. Gentle rinsing from the outside is a reasonable homeowner step. Deep cleaning belongs to a pro.
Stuck contactor. If the outdoor unit keeps running with the thermostat off, shut the system off at the breaker and call a pro. A stuck contactor can run the compressor with no control.
Undersized or leaky ducts. If one room never cools, the unit may be fine and the ducts the problem. See why a bedroom is too hot.
What can you safely try first?
- Set the thermostat to cool and a few degrees below the room temperature.
- Replace a dirty filter.
- Check that supply and return vents are open and clear.
- Look at the outdoor unit for debris, a blocked side or a fan that isn’t spinning.
- Give the system time. If it still can’t cool, stop and call.
Don’t keep running a frozen system. Shut it off so the ice can melt, then call. See AC freezing up for the steps.
When to call us
A system that runs nonstop and can’t cool the house needs a licensed pro, especially in summer. Learn more about AC repair and our Tucson area coverage. Call (520) 353-2520 and we’ll match you with a licensed local pro.