You're encountering issues with your Whirlpool refrigerator, model FRSS36AF25/3, which began after cleaning the coils. The initial startup seemed normal, but then you noticed two stripes on the freezer side. The compressor started about 10 minutes later and took several hours to bring the temperature down to -18°C. After reaching this temperature, the compressor stopped, but upon restarting, the temperature continued to drop, triggering the alarm. You've noted that all fans are operational, the evaporator isn't iced over, but the compressor is making a buzzing sound and is hot to the touch. After turning it off overnight and restarting, the same issue persisted.
The symptoms you describe suggest a few potential issues:
The buzzing sound and the heat from the compressor could indicate that it's overworking or struggling. This might be due to a problem with the compressor itself or a related component like the start relay or capacitor.
The fact that the temperature keeps dropping past the set point until the alarm goes off suggests a possible issue with the thermostat or temperature control system. It's not correctly regulating the temperature.
Since you've already checked for ice buildup and confirmed that the fans are working, it seems the issue is more related to the temperature control or the compressor.
Given the complexity of these potential problems, especially involving the compressor, it might be best to consult with a professional appliance technician. They can provide a more detailed diagnosis, especially since the compressor involves refrigerant handling and electrical components, which require specialized knowledge and tools. Remember, safety is crucial when dealing with electrical appliances, so it's advisable to seek professional help for such issues.