Block all the ducts leading to the refrigerator compartment.

**Title: Newfrost Refrigerator - Declining Cooling Performance and Continuous Operation**

**Fault Symptoms:** After more than four years of normal use, the frost-free refrigerator experienced a noticeable decline in cooling performance and remained operational for long periods without shutting down.

**Analysis and Maintenance:** Upon inspection, it was found that the bimetallic strip was damaged. After replacement, the cooling function returned to normal. However, after running for 8 hours and then stopping, the refrigerator could no longer restart. When the freezer compartment was opened, the indoor temperature was found to be very high. The bimetallic strip was removed and tested, revealing that the 75°C thermal fuse had blown. A new bimetallic strip was installed, but after 8 hours, the same fault reoccurred. Initially, it was determined that the fault was caused by the damage to the bimetallic strip, which prevented automatic defrosting, leading to ice buildup on the evaporator. After 8 hours of operation, the air duct leading to the refrigeration compartment became completely blocked, causing a significant increase in the temperature inside the refrigeration compartment and preventing the compressor from stopping for extended periods.

Further analysis revealed that when the refrigerator was first turned on, the bimetallic strip was in an open state, so the timer motor did not run. However, at this point, the compressor had already started working and cooling. Once the temperature in the freezer dropped low enough to close the bimetallic strip, the timer motor began to run and automatically timed. After about 8 hours, it automatically switched to the defrost position. At this point, the compressor stopped, and the timer motor also ceased to run. After the frost melted, the bimetallic strip opened, energizing the timer coil, allowing the timer motor to continue running. After about 3 hours, it automatically switched back to the cooling position, and the compressor resumed work. This cycle repeated, with the refrigerator defrosting approximately every 8 hours to achieve automatic defrosting.

Upon closer inspection of the newly installed bimetallic strip, it was discovered that its wiring configuration was opposite to the original model. When the temperature dropped low enough to close the bimetallic strip, the defrost timer coil was energized and began operating. After about 8 hours, it automatically entered the defrost process. The power supply formed a circuit through the bimetallic strip to start defrosting, simultaneously short-circuiting the timer coil, causing the timer motor to stop running. As a result, the defrosting continued indefinitely, and the temperature in the freezer kept rising until the thermal fuse eventually blew, stopping the defrosting process.

**Repair Measures:** The bimetallic strip was desoldered, the wire ends were swapped, and it was resoldered securely. The refrigerator was then tested again and returned to normal operation, resolving the fault.

**Source of Article:** Beijing Newfrost Refrigerator Repair Center

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