### Fault Phenomenon:
The cooling function operates normally, but heating does not work. When the temperature is adjusted to the highest setting, the heating function still fails to start.
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### Analysis and Maintenance:
This air conditioning system's cooling and heating modes are controlled separately by control relays J1, J2, and temperature control relay J3. When J2 is energized, the normally open contact connected in series with the cooling control relay closes, while the normally closed contact connected in series with the heating control relay opens.
It is suspected that there is a fault in the temperature control circuit, which causes J1 to remain energized and unable to close J1-1. Using a multimeter on the ohms setting to measure J1-2 in the powered-off state reveals an open circuit, indicating that J1 is functioning properly. J1 is driven by the comparator LM3393. The voltage at its non-inverting input terminal relative to ground is measured as 2.2V, while the inverting input terminal relative to ground is 2.9V, suggesting that the thermistor Rt is damaged. After unplugging the connection plug for Rt, the fault persists, leading to the conclusion that capacitor C2 has a leakage issue.
**Technical Source:** Beijing AUX Air Conditioning After-sales Service Phone: [http://blog.tianya.cn/blogger/blog_main.asp?BlogID=3486891](http://blog.tianya.cn/blogger/blog_main.asp?BlogID=3486891)
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### Problem Description:
AUX cabinet-type air conditioner, normal cooling function, but no heating function.
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### Solution:
After replacing the faulty components with new ones, the fault was eliminated.