First, try these two troubleshooting methods if your air conditioning and/or heat pump system are not coming on:
Check Your Thermostat
- Determine if you can read the temperature and other information on the thermostat display.
- Make certain that the thermostat indicates that the system is on and set to the cooling or Air Conditioning mode.
- Adjust the set temperature down some a few degrees to check if the system responds and starts to come on.
- You can check the thermostat by turning the fan to the “On” or “Run” setting. If the fan does not respond, then the signal from the thermostat either didn’t reach the control board or the control board is bad, or the control board fuse is bad.
Check Your Power
- Locate the electrical panel and reset the breaker(s). Make certain you move them all the way to the complete “Off” position and then back to the complete “On” position. Be aware that some circuit breakers may not look like they are tripped off.
- Locate the air conditioning/furnace or heat pump power switch. This is usually located near the furnace or unit base inside, near where the blower and indoor evaporator coil are installed. This looks like a simple light switch. It may have accidentally been switched off.
- It is possible the power interruption to the air conditioner or heat pump is due to a blown fuse in the emergency disconnect switch outside near the condenser unit
If these troubleshooting solutions do not work, the issue will be one of the below four options. These will require the guidance of a professional HVAC technician.
Condensate Emergency Shutoff Switch: Condensate Water on the Floor
Some systems have a positional float switch or moisture sensing switch that shuts off the air conditioning system or heat pump when the drain pan becomes full and prevents it from starting again. The purpose of the system shutoff switch is to avoid condensate water from overflowing onto the floor and surrounding area. This is usually caused by a clogged drain line or dirty drain pan.
A capacitor controlling the compressor and/or condenser unit fan has failed so the compressor cannot be started or run properly. This may also be indicated when after you set the thermostat down a few degrees, you can hear the system begin to start but it never quite comes on or stops.
This can sometimes be heard at the outdoor unit as a hum. Sometimes instead of a hum, you may hear a slight initial rumble of the compressor. This may go on for a couple of minutes and then cut off, because the compressor may cut off if the fan won’t be moving the air through the condenser.
The contactor switch that controls the proper voltage and current to the compressor and condenser fan and has failed so the compressor cannot be started or run properly.
When the temperature rises enough above the set point, the thermostat sends a signal to the contactor to turn on the compressor and condenser fan motor. This may be observed at the outside unit by a rapid clicking or hum at the unit where voltage is being applied but the switch cannot quite engage.
Compressor Not Operating
The air conditioning or heat pump compressor is not working. This may mean that one of the following circumstances have occurred:
- The compressor has reached a high temperature due to working so hard to compress and circulate the refrigerant gas that it became too hot and reached a thermal limit – a condition known as thermal lockout. This condition, the accompanying diagnostic code, and status message may be displayed on your thermostat.
- The compressor may indeed be a failed or bad compressor that needs to be replaced.
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