The outdoor unit of the air conditioner also has two temperature sensors, one of them is to detect the temperature of the condenser of the outdoor unit. This temperature sensor is usually installed on the surface of the condenser, and the installation method is similar to the indoor evaporator. Another temperature sensor is placed on the air inlet of the condenser to detect the outdoor ambient temperature, which is used to control the speed of the outdoor fan and preheat the compressor in winter. The two temperature sensors are installed as shown in Figure 1-4.

Figure 1-4 Position of Condenser Coil and Outdoor Unit Temperature Sensor

The temperature adjustment of the condenser is mainly divided into two parts: heating defrosting and refrigeration condensation. During heating, the first defrosting of the condenser is a timed defrosting (generally 50 minutes), and the subsequent defrosting is controlled according to the temperature of the outdoor condenser. If the temperature is lower than a specified temperature such as -11 °C, defrosting is required. During cooling, if the detected condenser temperature reaches 68°C, the compressor stops working to prevent the condenser coil from overheating.

In this process, the outdoor condenser coil temperature sensor has three main functions:

• Protection against overheating during cooling
• Protection against freezing during heating
• Temperature control of the condenser during defrosting

The outdoor condenser temperature sensor mainly uses a 20K resistance NTC thermistor (the resistance may be different from different manufacturers), and its circuit schematic diagram is similar to that of the indoor evaporator coil temperature sensor (see Figure 1-3).