AC malfunction and failures

There are a number of problems that can cause the same malfunctions in your AC equipment, making diagnosis difficult.

The causes of AC malfunction and failures are varied. Many have their ultimate cause in a poor installation, in wire corrosion or in electrical connections damaged by overuse and strain... But poor maintenance, dirty filters, or buttons in the wrong position are the immediate causes of most AC failures...

On/Off switches and button positions

There are some simple solutions and checks that you can attempt, before calling an AC professional to your home. If you AC equipment is not blowing cool air...

- Check the thermostat. See if it is set in the "Cool" position.

- Check the outdoor air conditioning (condensing unit): the circuit breakers in the electric panel or the circuit breaker box should be in the "On" position.

- Check the "disconnect switch" of the outdoor unit. Is it in the "On" position?

- Check the blower motor in your furnace. Is it running? If the thermostat is in the "cool" position, it should be running...

- Check the return air grilles. They shouldn't be blocked...

- Check the supply air registers. Are they open and blowing air? Aren't they blocked by furniture?

Filters and AC Malfunction

Blocked filters are a common cause of air conditioners malfuction (they cause the AC shut down for lack of proper airflow).

So, check the air conditioner filters. Filters should be replaced regularly. See: Central and Window AC filters

Poor AC maintenance

Inadequate refrigerant charge, dirty coils or a dirty blower are also possible causes of AC malfunction and failures.

Regular maintenance of your AC equipment is crucial to avoid such problems.

See:
Air Conditioners Malfunction
Room and Central AC filters
Air Conditioners Refrigerant
Cleaning Air Conditioning Coils
AC Blower
Window air conditioner maintenance

Fuses and circuit breakers

In troubleshooting, check the AC circuit breakers and fuses. Before resetting the breakers, let the unit cool down for some few minutes.

Compressors malfunction

If the central air conditioner compressor stopped, the high-pressure limit switch may have tripped. Check the high-pressure limit switch, and reset it by pushing the button.

Electric Control Failure

Wire terminal corrosion is common, and a cause of AC malfunctions. Electrical connections and contacts may be damaged by overuse and strain, especially if the air conditioner is oversized, causing the equipment to turn on and off too frequently.

Problems with the Sensors

If your room air conditioner behaves erratically or cycles constantly, inspect the thermostat sensor (usually located in the control panel). See if it is well positioned. The sensor should be near the coil, but without touching it; if it doesn't, reposition it by carefully adjusting its wire.

Drainage Problems

Check the condensate drain. See if it isn't clogged and draining improperly. This is very common in room air conditioners mounted unlevel.

Other causes AC malfunction

Air conditioned equipment might be affected by open windows and doors (or even leaky windows).