Guide: HVAC
AC blowing warm air? Five checks, then call.
Check the thermostat is on "cool" and set below room temperature, replace a dirty filter, and make sure the outdoor unit is running and not iced or blocked. If the outdoor fan is not spinning, the lines are frozen, or it still blows warm after the filter change, turn the system off and call an HVAC tech.
Connects you to an independent HVAC company. Home Service Lab does not perform the work and does not set the price.
Check these first
- Thermostat. Mode on "cool", fan on "auto", set a few degrees below the room. Replace the batteries if the screen is blank or dim.
- Air filter. A clogged filter starves the system of air. The US Department of Energy says to clean and replace the filters regularly.
- Breakers. Central AC usually has two: one indoors for the air handler and one for the outdoor unit. Reset a tripped one once.
- Outdoor unit. Is the fan spinning? Clear leaves, grass and anything stacked against it.
- Ice on the lines. Frost on the copper lines or indoor coil means it is freezing up. Switch to "off" (fan on) to thaw it and call.
Do not keep running a system that is iced up or tripping its breaker. It can damage the compressor, which is the most expensive part.
Signs it is a technician job.
Outdoor fan not turning, a humming or clicking unit that will not start, ice on the lines, water leaking from the indoor unit, or a breaker that trips again after a reset. Low refrigerant, a failed capacitor and a frozen coil are all common and all need an HVAC tech.
If it has been a while since anyone serviced the system, say so when you call.
Questions
Common questions
My AC is blowing warm air. Who should I call?
An HVAC technician. If the thermostat, filter and breakers check out and it is still blowing warm, the cause is usually inside the system, such as refrigerant, a capacitor or a frozen coil.
Can a dirty filter make the AC blow warm air?
Yes. Restricted airflow can make the coil freeze, and a frozen coil stops cooling. Change the filter, let the system thaw with the fan running, and call if it does not recover.
Being straight with you
We connect the call. We do not do the work.
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Local pages
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