Check the thermostat mode and setpoint, whether air is moving, and whether an accessible filter is overdue for replacement. Ice, burning smells, repeated breaker trips or indoor water leaks are reasons to stop troubleshooting and request service.
“The AC is running” can mean the indoor fan is running, the outdoor equipment is running, or both. Describing those separately helps narrow the problem. A system can move room-temperature air even when its cooling equipment is not operating.
First, confirm that the thermostat is asking for cooling
Select Cool and a setpoint below the displayed room temperature. A fan setting of On may circulate air between cooling cycles; that air will not always feel cold. If the thermostat displays a delay message after a power interruption, follow its manual and allow the delay to finish.
Avoid setting an extremely low temperature to force a faster result. Record the current room temperature, the target and any message before changing settings. If the thermostat has gone blank, note that separately rather than assuming the compressor has failed.
Reference: Trane: air conditioner troubleshooting
Separate weak airflow from warm airflow
With the system off, check only the filter location intended for routine homeowner access. Replace a dirty disposable filter with the specified size and type. Keep supply registers and return grilles unobstructed. Observe the outdoor unit from a safe distance without opening a panel or reaching through a grille.
| Pattern | Useful observation |
|---|---|
| Little or no air at every register | Record filter condition and whether the indoor fan operates. |
| Normal airflow but no cooling | Record whether outdoor equipment appears to run. |
| Only one room is uncomfortable | Note closed doors, blocked registers and which other rooms cool normally. |
| Ice or water at indoor equipment | Turn cooling off and arrange service. |
When settings and filters are not the answer
Cooling problems can involve airflow, controls, refrigerant or electrical components. Low refrigerant is not established by warm air alone, and adding refrigerant without finding a leak does not address the cause. These checks need appropriate tools and training.
Do not chip ice off a coil, pressure-wash equipment or try to spin a stopped outdoor fan. Leave electrical and refrigerant work to a qualified technician.
Reference: Trane: air conditioner troubleshooting
Prepare a clearer service request
Tell CMP whether the issue began suddenly or gradually, whether both indoor and outdoor equipment appear to run, and whether the whole San Jose property is affected. Mention any recent outage or maintenance. This gives the visit a useful starting point without treating a symptom as a confirmed diagnosis. If indoor heat is becoming unsafe, move to a cooler location while arranging help.
Common questions
Why does the fan run when the AC is not cooling?
The fan can circulate air independently of a cooling cycle. Check the fan setting, but remember that controls, outdoor equipment and other faults may also prevent cooling.
Does warm air mean I need a new AC?
No. A diagnosis is needed before comparing repair with replacement. Settings, airflow and repairable component problems can also cause warm air.
Plumbing, heating, air conditioning and electrical service for San Jose homes and businesses. Get to know CMP.
This guide covers general observations and planning. Equipment instructions and an on-site assessment determine the appropriate work for your property.