Service ExplainersAir conditioner not cooling
The handful of causes behind most no cool calls, the three things a homeowner can safely check, and the symptoms that mean you should stop and call a technician.
By Elijah Canfield, Founder, Hire Best Pros · Updated August 26, 2026
Elijah Canfield is the founder of Hire Best Pros. He writes and edits the site's consumer guides, with a focus on how home service and moving projects are priced, scoped and compared.
Most no cool calls come down to airflow, power, controls or refrigerant. Before calling, check the thermostat mode and batteries, check that the breaker has not tripped, and check whether the filter is dirty enough to choke airflow. If the outdoor unit is silent, if the indoor coil is iced over, or if the system runs but never cools, that needs a technician.
Key points
- A dirty filter is the single most common cause of poor cooling.
- Ice on the coil or line means turn the system off and let it thaw before anyone works on it.
- Low refrigerant means a leak. Topping it up without finding the leak is a temporary fix.
Three safe checks
- Thermostat: set to cool, set below room temperature, fresh batteries, schedule not overriding you
- Power: check the breaker for both the indoor air handler and the outdoor unit, and the service switch near the outdoor unit
- Filter: hold it to a light. If light does not pass through easily, replace it and give the system time to recover
Symptoms and what they usually point at
| What you notice | Usual direction |
|---|---|
| Air from vents is not cold | Refrigerant charge, compressor, or a frozen coil |
| Air is cold but weak | Airflow: filter, blower, closed or leaking ducts |
| Outdoor unit silent, indoor fan running | Power to the condenser, capacitor, contactor, or control signal |
| Ice on the refrigerant line or coil | Airflow restriction or low refrigerant. Shut it off and let it thaw |
| System runs nonstop and never satisfies | Undersized, dirty coil, duct losses, or a failing component |
When to stop and call
Anything involving refrigerant, the sealed system, the capacitor or wiring belongs to a licensed technician. Give them the details when you call: system age, what you already checked, what changed and when.
House not cooling down?
Find HVAC helpPreventing the next one
A large share of summer breakdowns trace back to skipped maintenance: a clogged filter, a dirty outdoor coil, or a condensate drain that backs up and trips a safety switch. Our HVAC maintenance guide covers the routine that catches these before they turn into a hot afternoon.
Common questions
- Should I hose off the outdoor unit?
- Gently rinsing debris from the outside of the coil fins with the power off can help airflow. Do not use a pressure washer, do not bend the fins, and leave the electrical compartment alone.
- Why does my system freeze up?
- Usually restricted airflow or low refrigerant. Both cause the coil to run below freezing. Turn the system off, run the fan to thaw it, replace the filter, and have a technician find the cause if it happens again.