Air Conditioner Temperature Sensor

How to judge the resistance value of the air conditioner temperature sensor?

Air conditioning circuit designers use room temperature 25℃ as the reference, that is, at 25%, RTI=RI、RT2=R2, the voltage at points A and B is 2.5V.Some circuits are equipped with R3 and R4, which mainly play a buffering role.When the ambient temperature rises, the RTI resistance decreases and the voltage at point A rises. The comparator outputs a differential voltage, which is processed by the CPU to control the operating state of the internal and external machines.

The sampling voltage of the external control board of large air conditioners and variable frequency air conditioners, and the temperature sensor connected to the VI is not 2.5V, but 1/4 of the power supply voltage, which is 1.25V.

In fact, there is a very simple way to determine the resistance value of the thermistor. Choose a 50K battery.A universal plug for the positioner and a thermistor, for convenience, a long wire can be used between them.After the connection is complete, unplug the thermistor of the air conditioner, plug in the universal plug, power up the air conditioner, use a multimeter 5V to test the voltage of both ends of the potentiometer, slowly turn the handle of the potentiometer, when the voltage is 2.5V, stop rotating, at this time the resistance of the potentiometer is the resistance of the thermistor.

For example: the resistance value is 8K and the ambient temperature is about 30°C, then the resistance value of the temperature sensor is 10K.

How to judge the quality of the air conditioner temperature sensor?

1. The resistance value of the indoor ambient temperature sensor becomes larger, causing the air conditioner to start frequently.
2. The resistance value of the indoor pipe temperature sensor becomes smaller, which causes the whole machine to be protected after starting.
3. The indoor ambient temperature and tube temperature sensing performance change, causing the air conditioner to work abnormally.
4. The temperature change value of the indoor pipe is 0Q, which causes the remote control of the whole machine to start unresponsive.
The sensor failure of the thermostat accounts for a relatively large proportion of the air-conditioning failure. To accurately judge, it is first necessary to understand its function. The air-conditioning control part is equipped with three temperature sensors.:
1. Room temperature sensor: it mainly detects the indoor temperature. When the indoor temperature reaches the set requirements, it controls the operation of the internal and external machines. When cooling, the external machine stops, the internal machine continues to run, and the internal machine stops after blowing waste heat during heating.
2. Indoor pipe temperature sensor: it mainly detects the coil temperature of the indoor evaporator, and plays the role of anti-cold air, anti-overheating protection, and automatic temperature control during heating.
3. Outdoor defrosting temperature sensor: It mainly detects the temperature of the outdoor condenser coil. When the temperature of the outdoor coil is lower than -6°C for 2 consecutive minutes, the internal unit turns to a defrosting state. When the resistance value of the outdoor coil sensor is too large, the indoor unit cannot work normally.

Analysis of the reasons for the inconsistency between the display temperature of the air conditioner and the actual perceived temperature

1. The remote control setting is incorrect;
2. The filter is not cleaned in time;
3. There are items in the air-conditioning inlet and outlet that affect the heating effect, and the room has a heat source or there are many indoor personnel, resulting in poor cooling effect.;
4. Poor room insulation effect;
5. The indoor power supply voltage is too low, resulting in low air conditioning efficiency.;
6. The ambient temperature is too high or too low, resulting in poor effect.

Precautions

During the maintenance of air conditioners, the proportion of temperature sensors (thermistors) fails is high. Once there is an open circuit, a short circuit, or a poor characteristic curve, the air conditioner will display an abnormal code and will not work properly.Since the parameters and resistance values are not indicated on the temperature sensor, it is often difficult to determine during maintenance. Even if the same brand and different models are used, the resistance values may not be the same.
Temperature sensor, that is, the resistance value decreases when the temperature rises; the resistance value increases when the temperature drops.The sampling voltage of the negative terminal of the CPU comparator is 1/2 of the CPU power supply voltage, which is 2.5V.The pull-up resistors at the positive end of the peripheral circuits RTI and RT2 op amp comparators, R1 and R2 are the lower bias resistors.