The air conditioner compressor overheat protection detects the temperature of the windings, casing, and exhaust outlet in real time through a temperature monitoring device. When the temperature exceeds the preset value, power is cut off to stop the compressor; after the temperature drops to a safe range, it can be reset automatically or manually. Common causes are as follows:
1. Dirty or blocked condenser
The condenser is easily exposed to impurities over time, causing the fins to become blocked and heat exchange efficiency to decrease. The high-temperature, high-pressure refrigerant discharged by the compressor cannot dissipate heat effectively, causing the exhaust temperature to rise and triggering overheat protection. This is common in dusty areas, areas with a lot of poplar catkins, or air conditioners that have not been maintained for a long time, where the outdoor unit's air temperature is abnormally high and the unit feels hot to the touch.
2. Cooling Fan Malfunction
A malfunction of the outdoor unit's cooling fan causes a sudden drop in heat dissipation efficiency. Common faults include motor winding burnout, bearing seizure, capacitor damage, and blade deformation or breakage, which manifest as the fan not spinning, low rotation speed, or abnormal noise. The condenser cannot effectively dissipate heat, and the compressor temperature rises rapidly, triggering protection.
3. Harsh Environmental Heat Dissipation Conditions
If the outdoor ambient temperature is too high and exceeds the air conditioner's design conditions, the heat load of the condenser surges, heat dissipation efficiency decreases, condenser pressure rises, and the compressor discharge temperature exceeds limits, triggering protection. Frequent protection occurs during high-temperature periods, while it is normal in the morning and evening.
4. Insufficient refrigerant (low Freon)
Air conditioning pipeline leaks or insufficient charging can lead to a reduced amount of refrigerant in the evaporator, causing the evaporation temperature to rise, the temperature of the refrigerant vapor entering the compressor to increase, and the motor coil to overheat, triggering protection. In hot summer, slight refrigerant loss is difficult to detect, and it is easy to blindly overcharge. This can be assisted by measuring the temperature of the compressor discharge pipe and suction pipe.
5. Excess refrigerant (too much Freon)
Charging the refrigerant beyond the rated amount causes the evaporator pressure and temperature to rise, increasing the system pressure and placing a heavier load on the compressor. In high-temperature environments, excess refrigerant leads to heat dissipation difficulties, increased compressor operating current, and triggers overheat protection.
6. Expansion valve blockage
The expansion valve may be blocked by rust, welding slag, or other debris, causing excessive throttling, high high-side pressure and low low-side pressure. The air blown out by the outdoor unit fan becomes hot to the touch, the evaporator does not fully condense, cooling efficiency is poor, the compressor load is high, it overheats severely, and protection is frequently triggered.
7. Dry filter blockage
The dry filter absorbs too many impurities and moisture, creating flow resistance, which causes abnormal system pressure distribution. The compressor discharge temperature rises, triggering protection. This is accompanied by a decrease in system cooling capacity. Severe blockage can interrupt the refrigerant circulation, causing instant overheating protection of the compressor.
8. Four-way valve cross-flow
The compressor relies on low-temperature return gas for cooling. Normally, low-temperature, low-pressure gaseous refrigerant enters the compressor for cooling. Cross-flow through the four-way valve disrupts normal refrigerant flow, causing the compressor to intake hot gas, preventing cooling and causing temperature rise. If the temperature exceeds the thermal protection limit, thermal protection will be triggered.
9. Compressor starting component failure
When the start capacitor capacity declines or the start relay contacts are burned, the compressor draws excessive current upon startup. This can cause overheating of the motor windings or prevent normal startup, triggering protection. A typical symptom is that after the air conditioner is turned on, the outdoor unit makes a "buzzing" sound but the compressor does not operate. Replacing the starting components can restore normal operation.
10. Temperature Sensor Fault
A malfunctioning temperature sensor can drift and transmit incorrect signals, and faults in the mainboard control circuit can cause unstable power supply to the compressor. This manifests as the compressor having a normal temperature but frequently triggering protection. It is necessary to check the mainboard voltage and the sensor resistance for troubleshooting.
11. Lubrication System Failure
The compressor's internal mechanical components need to be lubricated with refrigerant oil. If the refrigerant oil is insufficient, deteriorated, or contaminated with impurities, it will reduce lubrication effectiveness, increase friction between mechanical parts, generate a large amount of frictional heat, and trigger overheating protection.
