1.When was the last time you changed the batteries in the thermostat?
If the thermostat back light doesn’t light up or is flashing, you should change the batteries.
2.Have you checked the indoor units air filter?
Airflow throughout your unit is vital, and it is important for your filters to be changed regularly. If the filter is not changed regularly, the restriction of air can cause the A/C unit to “freeze up” and blow warm air.
3.Is there power to the equipment?
We get multiple calls every year where we show up only to find out that the unit has no power. This could cause some bad feelings when the service technician wants to collect diagnostic or trip fees for a service call just to say, “You’re all set, we turned the power back on.”
4.Have you checked the “service man’s switch” on the indoor unit?
Local code may suggest that there should be an on-off switch or a “service man’s switch” next to the indoor air handler unit for safety. If you can access the location of the air handler (the indoor unit) take a look before you call a technician.
5.Did you check the electrical disconnect to the outdoor unit?
For much of the same reasons listed above, there should be a disconnect at the outdoor unit as well.. Make sure it is on. ONLY if you are confident in what you are doing. This switch or disconnect is controlling 240 volts of electricity to the outdoor condensing unit and it is enough voltage and amperage to be very dangerous.
If these five steps are not comfortable for you or not a solution, it’s time to call for service.