When the Changhong air conditioner is turned on for heating, it cools instead of heating.
Fault phenomenon: When the machine is turned on for heating, it not only fails to heat but also cools down.
Analysis and Maintenance: The ability to cool indicates that the compressor and power circuit are basically normal, suspecting a fault in the control circuit. The control circuit of this machine uses NEC's microcomputer chip uPD57028 as the main controller, installed near the indoor control board. The temperature sensor TR2 is a negative temperature coefficient thermistor, which has the characteristic of increasing or decreasing resistance with the decrease or increase of room temperature. It forms a voltage divider circuit with resistor R19, dividing the +5V voltage and directly sending it to pin 26 of uPD57028 as the control signal voltage to compare with the set temperature signal voltage, and outputs a high-level heating instruction from pin 60. After detecting that the high-level output of pin 60 is normal, the fault range is narrowed down to the circuit after pin 60. The high level output from pin 60 enters the inverter through pin 5 of IC2, is inverted, and then output through pin 12, connecting the reversing valve relay Y1 coil, Y1 pulls in, the contact closes, the reversing valve is energized and reverses direction, achieving the switching between cooling and heating.
After the above analysis, upon checking after turning on the machine, there was no sound of Y1 pulling in, indicating that Y1 did not pull in. After removing it for inspection, it was found that the coil was open circuit.
Handling method: After replacing the reversing valve relay Y1, the fault was eliminated.
Article source: Beijing Changhong Air Conditioner Repair Phone http://blog.tianya.cn/blogger/blog_main.asp?BlogID=3766321.