Why Does My AC Compressor Turn on and off Repeatedly?

Figure 1: Air conditioner indoor unit.

Under the control of the thermostat, generally the air conditioner will stop working when it reaches the set temperature. For example, when the indoor temperature is 35 °C, you turn on the air conditioner and set it to cooling mode, and set the cooling temperature to 26 °C, and the air conditioner will start to work normally.
The air conditioner continues to run, and when the indoor temperature drops to about 25 °C, the air conditioner will stop working. Once the indoor temperature rises above a certain range of 26 degrees, it will automatically restart the work.

The working process shows that the air conditioner compressor will indeed stop after working for a period of time, but it will restart again after a period of stopping. If it does not restart after stopping, it means that there is a fault. In addition, if the time interval between the start and stop of the air conditioner compressor is too short, that is, frequent start and stop. This is also a phenomenon of air conditioner failure, which we call “short cycling".

So what will cause the short cycling of the air conditioner?

1. Reasons for AC Compressor Keep Turning on and off

When the fixed-frequency air conditioner is working, and the indoor temperature reaches the set temperature, the outdoor unit will stop. When the indoor temperature rises, the air conditioner will start to cool again. But if the air conditioner compressor starts and stops frequently, it is not normal. What are the specific reasons?

1.1 Oversized AC Unit

This may be related to the selection of the air conditioner—— the greater the cooling capacity of the air conditioner, the faster the cooling speed. If a large air conditioner is used in a small room, the cooling capacity generated by the air conditioner can quickly lower the indoor temperature, and then the air conditioner is turned off.
If coupled with the poor insulation of the room, the indoor temperature will rise again soon, and the air conditioner will start again. That will cause a short cycling of the air conditioner.

To avoid this situation, it is necessary to choose the right size of the air conditioner, and do not blindly be greedy for large ones.

Table 1: Air conditioner selection chart.

1.2 Temperature Sensor Failure

There are generally three temperature sensors in the air conditioner (some models of air conditioners have more), which are located in the indoor unit, pipeline and outdoor unit. After the temperature sensor is garbled, it cannot accurately measure the temperature, which may cause the air conditioner compressor to start and stop frequently.

1.3 Compressor Overheating

Compressor overheating may cause short cycling. There are many reasons for the overheating of the compressor. After overheating, the compressor will start the protection shutdown function, and it will start again when the temperature drops. Conditions that may cause the compressor to overheat are as follows.

Abnormal Pipeline Pressure

If the pressure in the air-conditioning pipeline is too high or too low (generally, the compressor heats up because it is too high), it may cause the compressor to overheat. The possible causes of abnormal pipeline pressure are: pipeline blockage, pipeline damage, refrigerant abnormality—— too much refrigerant, etc.

Figure 2: Bent AC copper pipe.

Electric Leakage

There is a capacitor in the outdoor unit, and if the capacitor is damaged, the capacity will drop, which will cause electric leakage. Leakage current moving through the compressor will cause the compressor to heat up.

Fan Motor Failure

The fan motor of the outdoor unit will generate heat during operation, but under normal circumstances it will not cause the compressor to overheat. Once the starter fails, it will increase the heat generation of the fan motor. In light cases, the compressor will overheat, and in severe cases, the fan motor will be directly burned. After the motor is burned, the heat generation will be higher.

Lack of Refrigerant

After the system is short of refrigerant, running for a long time will cause the discharge temperature of the compressor to overheat, causing the thermal overload switch to trip.

In addition, too high ambient temperature, broken compressor overheat protection device, etc. will also cause the compressor to overheat. As long as the compressor temperature is lowered, it can be started. Generally, the compressor can be watered to cool it down quickly, and then find the cause of triggering its protection function.

Dirty Condenser Coils

The condenser is directly behind the outdoor unit—the aluminum fins of the outdoor unit. If the heat dissipation is not good, the temperature of the refrigerant in the compressor will be too high. Cleaning the aluminum fins of the outdoor unit can solve the problem.

Figure 3: Clean car AC condenser.

1.4 Electrical Problems

The electric circuit problems include:
1. The control circuit board is faulty.
2. The temperature sensor is overloaded and the measured information is wrong.
3. The power wiring is loose or in poor contact.
4. The start capacitor or compressor start coil is burnt out.

1.5 Other Reasons

1. It may be that the cooling temperature of the air conditioner is set too high, causing the air conditioner to reach the preset temperature too early and stop cooling. You can lower the temperature of the air conditioner appropriately.

2. It may be that the air conditioner has turned on the sleep mode, and the air conditioner will automatically adjust its operation according to the ambient temperature.

3. It may be that the air conditioner voltage is unstable, causing the air conditioner compressor to start and stop frequently due to insufficient voltage, and it is necessary to wait for the voltage to stabilize before using it.

4. It may be an internal fault of the air conditioner compressor. If it is found that the air conditioner compressor is damaged after inspection, it is recommended to contact the after-sales service or a professional third-party maintenance agency to replace the air conditioner compressor.

6. After the evaporator or filter screen is dusty and fouled, the airflow becomes smaller, causing the system pressure and temperature to become unsteady.

Figure 4: Clean air conditioner indoor unit.

2. Conclusion

After the air conditioner fails, the indoor temperature is usually not the set temperature - either too high or too low. The frequent shutdown of the air conditioner caused by the fault not only results in significant energy consumption and shortens the lifespan of the air conditioner, but also greatly reduces the comfort in the room.

Most air conditioners will display a fault code in the temperature display area of the indoor unit after it fails, such as E1, E2, P1, P2... Different brands of air conditioners have different meanings of the fault codes, and you can refer to the air conditioner instruction manual for details.

Through the above description, do you have a new understanding of the short cycling problem of air conditioning compressors? Do not panic when encountering such failures of air conditioning compressors, because such failures are repairable, and you can call the maintenance master for help.

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