Source: http://blog.163.com/geliktiao_2012
Fault Phenomenon: The compressor cools normally but does not heat.
Analysis and Maintenance: The control circuit of the machine uses a microcomputer chip PD75028 as the main controller, and its heating function is designated by the signal output from pin 60 of the chip. Therefore, the focus should be on checking whether there is a high-level output at pin 60 of the chip, whether the resistance value of the indoor sensor is normal, and whether there is a 220V voltage between the blue wire and the green wire in the outdoor unit wiring and the signal line.
Upon inspection, it was found that there was no 220V voltage across the terminals of the reversing valve coil in the outdoor unit wiring. Upon opening the indoor unit circuit board, it was measured that there was a 220V voltage between the output terminal of the reversing valve control relay and the L terminal of the power wiring, indicating a fault in the signal line. Further checks revealed that the wiring at the pipe bend where the indoor unit passes through the wall had been tampered with, and the reversing valve control line (green) was found to be open-circuited.
Gree split-type air conditioner, unable to heat.
Repair Method: After replacing the wiring, the fault was eliminated.