Several common quick detection methods for air conditioner thermostats

When the air conditioner cannot operate normally, in addition to checking the compressor's start relay, overheat, overcurrent protector and capacitor, you must also check the air conditioner thermostat master control selection switch, which is a very important control protection and execution component in the electrical control system. Here are some common quick detection methods for air conditioner thermostats.

1. Bellows or diaphragm air conditioning thermostat

1. Fault phenomenon: The contact is in poor contact or burned, causing the circuit to fail to connect; the contact frequently moves and arcs and sticks, causing the circuit to fail to break; the temperature sensing agent in the temperature sensing chamber leaks, causing the contact to fail to move and lose control, etc.

Maintenance method: After turning the air conditioner thermostat knob in forward and reverse directions several times, use the multimeter R×1 to measure the two wiring terminals of the temperature controller when it is connected. If the resistance value is very small, it indicates that the contact is normal; if the resistance is very large, it indicates that the contact is poor; if it is not connected, it may be a leakage of the temperature sensor.

To check if there is leakage, you can first conduct an appearance inspection to see if the temperature sensing head is broken, whether the temperature sensing package is damaged or cracked, whether the temperature sensing tube has any bending marks, etc. Then put the temperature sensing package in 30-40°C warm water to test whether the contacts are closed. If the contacts are still not closed, it means that the temperature sensing agent in the temperature sensing package has leaked out; if the contacts can be closed, take the temperature sensing package out of the water, and leave it in a low temperature environment for a period of time. If the contacts are disconnected again, it means that the temperature adjustment range of the thermostat is not appropriate. You can correct it by adjusting the temperature range adjustment screw, turn it counterclockwise for 1, 2 seconds, and then try again.

2. Fault phenomenon: The contacts of the air conditioner thermostat are stuck due to ignition. The contacts cannot automatically jump open and the compressor cannot stop.

Maintenance method: put the temperature sensor package in the cold storage room (5～10℃) of the double-door refrigerator, and measure whether the two-wire terminals of the temperature controller are disconnected. If they are not disconnected, it means that the contacts are sticking. You can use a flat screwdriver to force the mechanical contacts to disconnect; if the contacts can jump, it means that the temperature control range of the thermostat is drifting and low, and you can adjust the temperature control range adjustment screw clockwise.

3. Fault phenomenon: Temperature sensing agent leakage

Maintenance method: Use a hot towel to heat the temperature sensing tube, adjust the knob to the lowest temperature, and use a multimeter to measure whether the switch of the thermostat is connected. If the switch is not connected, it means that the temperature sensing agent has leaked, and a new thermostat should be replaced.

2. Dual-purpose air conditioner thermostat

The thermostat used in electric heating air conditioners has two sets of contact mechanisms (cold contacts and hot contacts) in the contact control box. The same temperature-sensitive bellows is used to control the temperature. Its failure phenomenon and inspection method are basically the same as those of ordinary thermostats, but it should be noted that the cold and hot switching action should also be checked to see if it is sensitive, that is, the compressor circuit should be connected when in the cooling position, and the electric heater circuit should be connected when in the heating position.

3. Defrost air conditioner thermostat

The defrost temperature controller is a component set in the control circuit of a thermal air conditioner and is specifically used to switch the electromagnetic reversing valve.

Its temperature sensing tube is placed on the coil of the outdoor heat exchanger. When heating is performed in winter and the frost layer of the outdoor heat exchanger thickens and the temperature is lower than a certain set value, the contact of the defrost controller is activated.

Disconnect the electromagnetic reversing valve. Change the original heating cycle into a cooling cycle. There are two commonly used structural forms: one is the thermal bimetallic type; the other is the ordinary thermostat.

The detection method is to place the temperature sensing part in water or air of the corresponding temperature. Use a multimeter to measure whether the two terminals are disconnected or connected. Then you can know whether it is good or bad. Thermosensitive bimetallic thermostats are also used for indoor cold wind control.

4. Temperature Sensing Resistor

Electronic air conditioner thermostats or microcomputer-controlled air conditioners all use thermistors as temperature sensing elements.

Thermistor is a component whose resistance changes significantly with temperature. Thermistor used for measuring return air temperature of air conditioner generally has negative temperature coefficient characteristic: resistance value decreases with increasing temperature.

For thermistors used in air conditioners of a certain brand, the characteristics of the resistance changing with temperature are usually plotted in a chart in the manual for testing. During testing, semiconductor thermometers and multimeters can be used for measurement under certain conditions.

Compare the temperature sensing characteristic curve or characteristic value table to determine whether it is normal. When the thermistor ages and its performance drifts, that is, the corresponding relationship between temperature and resistance changes, a new thermistor sensor should be replaced.

The system may fail if it does not work properly or after long-term aging. During maintenance, the replacement method is sometimes adopted, that is, replacing the thermostat with a good one of the same model and specification, which not only saves maintenance time, but also makes it easy to identify the quality of the original thermostat.