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HomeRepair HelpCentral A/C RepairCentral air conditioner wall thermostat not working properly Repair
Central air conditioner wall thermostat not working properly
When a thermostat is not working, the display is blank, or your thermostat is not turning on the AC, start with the wall thermostat itself. A failed wall thermostat is the most likely cause of an AC thermostat not working or not communicating with the furnace, air handler, or outdoor unit. A failed wall thermostat can cause the same symptoms, including an air conditioner not turning on when the system calls for cooling. Next, check the thermostat batteries, if equipped, and replace them when weak or dead. A faulty control board in the furnace or air handler is less common but may stop the thermostat from receiving 24-volt power. An incoming power problem, such as a tripped circuit breaker, blown fuse, or switched-off service disconnect, can also leave the thermostat blank. Damaged thermostat wire may prevent signals from reaching the indoor or outdoor unit; testing continuity is a practical DIY check. Turn off power before inspecting wiring, and leave 240-volt testing or repairs to a qualified technician. Enter your central air conditioner model number to find the exact replacement thermostat, wall thermostat, control board, or wiring for your system.
01 - Central Air Conditioner Wall Thermostat
The wall thermostat is responsible for controlling components and regulating the home's temperature. The thermostat can be powered with 24 volts from a control board on a separate unit like a furnace or air handler, or from batteries in the thermostat itself. The thermostat also has terminals to receive and distribute low voltage 24 volt power to run different HVAC products such as a furnace, air conditioner, or heat pump. If the wall thermostat is receiving power but the display is dead, or it will not send power out in the appropriate modes, the wall thermostat will need to be replaced.
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Highly Likely
02 - Central Air Conditioner Wifi Thermostat
The WiFi thermostat is responsible for controlling components and regulating the home's temperature. The thermostat is usually powered with 24 volts from a control board on a separate unit like a furnace or air handler. The thermostat also has terminals to receive and distribute low voltage 24 volt power to run different HVAC products such as a furnace, air conditioner, or heat pump. If the WiFi thermostat is receiving power but the display is dead, or it will not send power out in the appropriate modes, the WiFi thermostat will need to be replaced.
Highly Likely
03 - Wall Thermostat Batteries
Most wall thermostats are either powered by an enclosed battery or by the furnace or air handler control board. If the thermostat display is dead, you can remove the thermostat cover and look for replaceable batteries. Replace the batteries if needed and check operation.
Common
04 - Central Air Conditioner Control Board
The control board regulates the power supply to all of the components in the system. If the control board fails, it might not send voltage to the thermostat, leaving the thermostat inoperable.
Less Common
05 - Incoming Power Problem
Check to see if there is power to the furnace or air handler. One or more indicator lights on the control board should be illuminated. If there is no power to the furnace or air handler, check to see if a circuit breaker has tripped or a fuse has blown. Confirm the power switch on the side of the unit is turned on.
Less Common
06 - Bad Wall Thermostat Wiring
In order to send signals from and to the indoor and/or outdoor units, the wall thermostat uses a group of wires usually called thermostat wiring. If the thermostat wiring gets damaged, certain functions of the system or the thermostat itself may not function properly. The thermostat wiring can be checked for power or continuity with a multimeter. The wiring is usually industry standard colors: Red/White/Yellow/Green for a four-wire system.
Less Common
Frequently Asked Questions
Why is my central air conditioner thermostat blank or not working?
Why is my thermostat not turning on the AC?
How do I test a central air conditioner thermostat and its wiring?
Could a bad fuse, breaker, transformer, or control board cause thermostat problems?
How do I find the correct replacement thermostat for my central air conditioner?
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