If you're having trouble with your central air conditioner turning on automatically please go through the following steps.
1) Set the thermostat to "cool." Check that the displayed set temperature is well below the current temperature or the real temperature of the room.
2) Your central air conditioner should have its own dedicated 240-volt circuit. Locate the main electrical box (or panel) usually located on one of interior garage walls. Check for a tripped breaker or a blown fuse. If the air conditioner breaker is tripped or blown, reset or replace the fuse.
3) Check that the furnace power switch is in the on position. Next, look for a switch mounted on the outdoor unit. This is the condenser's on/off switch. Make sure that it's off. Now, make sure the 240-volt which is next to the compressor (it should be in a metal box typically located on the exterior house wall adjacent to the unit) is still on.
4) Make sure the power to the air conditioner is off. Now, check the thermostat. Take off the outside housing on the thermostat. Unscrew the Y terminal wire and turn the power back on.
5) Now we perform the tests. Grab the wire by its rubber covering. Do not touch the metal with your fingers. Take the metal exposed portion of the Y wire and hold it to the R terminal for a couple minutes. If the compressor turns on, you have a faulty thermostat. Call a technician. If the compressor does not kick on, turn the power off and call a technician.
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