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McQuay Air Conditioner is short cycling

If your McQuay air conditioner is short cycling, the unit starts, stops, and starts again before completing a normal cooling cycle. When an AC turns on and off quickly, the most likely causes on this McQuay symptom page are electronic control problems, starting with the control board, then the main control board, and then the user control and display board. These boards regulate voltage and commands to key components, so a failure can make the air conditioner keep cycling even when the cooling load has not been satisfied. Before replacing a board, check the temperature-sensing parts that tell the controls what the room temperature is. A bad thermistor or temperature sensor can send the wrong resistance reading to the board, and a faulty temperature control thermostat can shut the compressor off too soon or restart it before refrigerant pressure has equalized. Use a multimeter where appropriate and compare readings to the wiring diagram or service information. Enter your McQuay model number on RepairClinic.com to find the exact replacement control board, thermistor, temperature sensor, or thermostat for your specific air conditioner.

01 - McQuay Air Conditioner Control Board

The control board regulates the voltage to all of the air conditioner components. If the control board fails, the air conditioner may short cycle. Control boards are often misdiagnosed; make sure to check more commonly defective parts first before replacing the control board.

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Highly Likely

02 - McQuay Air Conditioner Main Control Board

The main control board regulates the voltage to all of the air conditioner components. If the control board fails, the air conditioner may short cycle. Control boards are often misdiagnosed; make sure to check more commonly defective parts first before replacing the main control board.

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Highly Likely

03 - McQuay Air Conditioner User Control and Display Board

The user control and display board allows the user to operate the unit by selecting fan speeds and cooling temperatures. If the board is defective, the air conditioner may short cycle. If the temperature sensor or thermistor tests appropriately with a multimeter, it's possible the user control and display board is malfunctioning and will need to be replaced.

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Highly Likely

04 - McQuay 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. A malfunctioning thermistor may cause the air conditioner to short cycle. 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 check...ing your user’s manual.)

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Common

05 - McQuay Air Conditioner Temperature Sensor

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

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Common

06 - McQuay 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, the air conditioner may short cycle. When the thermostat shuts the compressor off there needs to be approximately a five to ten minute delay to let the refrigerant equalize before the compressor will start again. If the refrigerant has not had time to equalize the compressor may not start. If the thermostat is short cycling it will need to be replaced. To determine if the temperature contr...ol thermostat is defective, use a multimeter to test it for continuity. If the thermostat does not have continuity, 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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Common

Frequently Asked Questions

Why is my McQuay air conditioner short cycling?

Can a bad thermistor cause my McQuay AC to turn on and off quickly?

How do I know if the temperature control thermostat is causing my McQuay air conditioner to keep cycling?

Should I replace the control board if my McQuay air conditioner short cycles?

How do I find the right replacement part for a McQuay air conditioner that is short cycling?

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