Simple checks first
Confirm COOL mode, a setpoint below room temperature, and the correct fan setting.
Check the filter and make sure supply and return grilles are open.
When the outdoor unit is not running
A capacitor, contactor, breaker, disconnect, control, compressor, or fan motor may have failed.
Repeated starting attempts should be stopped to prevent further damage.
Airflow and frozen coils
Dirty filters, blower problems, dirty coils, and restrictive ducts can reduce heat transfer.
A frozen coil eventually blocks airflow and may make the supply air feel warm.
Refrigerant problems
Low charge, TXV restrictions, filter-drier restrictions, or compressor problems can reduce capacity.
Airflow, superheat, subcooling, and system conditions should be evaluated together.
Repair versus replacement
Minor electrical failures may be straightforward.
Major coil or compressor repairs should be compared with equipment age, warranty, and replacement value.
Frequently asked questions
Can a thermostat cause it?
Yes.
Can a dirty filter cause it?
Yes.
Why only on hot days?
Peak load may expose a marginal system.
Should I add refrigerant?
Only after proper diagnosis.
Need a real diagnosis?
Get measurements, not guesses
Comfort Air Systems can test the actual equipment and explain the findings in plain language.