Power on, use a digital tester to measure the voltage, when the unit operates in cooling, it is 0V. When the unit operates in heating, it is about equal to power supply voltage. If the value of the voltage is not in the range, the PCB must be faulty and needs to be replaced. Turn off the power, use a digital tester to measure the resistance. The value should be 1.8~2.5 KÙ.
