Air conditioner has poor temperature control

If your air conditioner has a temperature control problem, runs too long, shuts off too soon, or the AC is not maintaining temperature, start with the parts that most often affect sensing and airflow. The most likely cause is a faulty temperature control thermostat, which monitors room air and switches power to the fan and compressor. If it loses continuity or cuts out too early, the air conditioner may not cool properly or remove moisture from the air. Next, check the air filter. A clogged or dirty air filter restricts airflow across the evaporator coil, reducing cooling capacity and potentially causing frost buildup. Clogged or restricted coils can create the same problem by making the unit run inefficiently. A bad thermistor can also cause an air conditioner thermostat problem or thermistor issue because it sends temperature information to the control board. Dirty condenser coils are another possible cause, especially if the compressor runs constantly while the room never reaches the set temperature. Enter your model number on RepairClinic.com to find the exact replacement thermostat, air filter, thermistor, or other part for your specific air conditioner.

01 - Air Conditioner Temperature Control Thermostat

The temperature control thermostat is a sensor which monitors the temperature of the air and activates a switch to provide power to the fan and compressor when the air temperature drops below a set point. If the thermostat isn’t working properly, the air conditioner may not stay running long enough to remove the moisture in the air and cool properly. To determine if the temperature control thermostat is defective, use a multimeter to test it for continuity. If the thermostat does not have continuity, or is shutting off too soon, replace it. (Note: Some thermostats may also control a heater and, as a result, will have three... terminals. Refer to your air conditioner’s wiring diagram for more information.)

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02 - Air Conditioner Air Filter

If the air filter is clogged, air cannot flow properly through the air conditioner. This greatly reduces the cooling capacity of the air conditioner. In addition, if the air filter is clogged, the evaporator coils will frost over. Most air filters used in stand-alone air conditioners can be cleaned with soap and water. Only filters that are extremely clogged with debris or damaged will need to be replaced.

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Highly Likely

03 - Dirty or Damaged Air Filter

If the air filter becomes clogged with dirt, it restricts air flow over the evaporator coils. If the air flow is reduced, the evaporator coils get too cold, which then causes the humidity in the room to condense on the coils and freeze. As frost accumulates on the coils, the frost restricts the air flow even more. Eventually, the entire evaporator coil assembly will frost over, causing the air flow to be completely restricted. Most air filters used in stand-alone air conditioners can be cleaned with soap and water. Only filters that are extremely clogged with debris or damaged will need to be replaced.

Common

04 - Clogged or Restricted Coils

Both the indoor and outdoor coils need to be clean for the air conditioner to work efficiently. A clogged or restricted coil will reduce air flow causing the unit to run inefficiently and longer.

Common

05 - Air Conditioner Thermistor

The thermistor is a sensor connected to the control board that detects the temperature of the air. The resistance value of the thermistor changes in conjunction with the air temperature. If the air temperature rises, the resistance value will decrease. To determine if the thermistor is at fault, use a multimeter to test it for continuity. If the thermistor does not have continuity, or if the resistance of the thermistor does not change with a change in temperature, replace the thermistor. (To find specific temperature and resistance values, try checking your user’s manual.)

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Less Common

06 - Condenser Coils are Dirty

The condenser coils dissipate the heat as the refrigerant passes through the coils. If the condenser coils are dirty, they won’t be able to dissipate the heat as effectively. As debris builds up on the coils, the air conditioner will become less efficient, causing the air conditioner to work harder to cool down. If the coils are significantly dirty, the air conditioner will not be able to remove the moisture from the air and maintain the proper temperature, resulting in the compressor running continuously in an attempt to cool the room. Check the condenser coils to determine if they are dirty. Refer to owner's manual for cleaning instructions.

Less Common

07 - Air Conditioner Control Board

The control board regulates the voltage to the compressor and the fan motor. If the control board fails, some components will not function properly or will not work at all. Control boards are often misdiagnosed; make sure to check more commonly defective parts first before replacing the control board.

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Less Common