**Abstract:**
Air source heat pump units have become increasingly popular in recent years due to their dual heating and cooling capabilities, as well as their ease of installation. However, the fluctuating working conditions caused by varying air conditioning loads and environmental factors often lead to prolonged operation under non-standard conditions. In some extreme cases, this has resulted in compressor failures. This paper presents a detailed analysis of common compressor failure issues observed during the actual operation of air source heat pump units and proposes practical improvement measures to enhance system reliability.
**Keywords:** Heat pump; Compressor failure; System reliability
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**1. Introduction**
Air source heat pump systems are widely used for their efficiency, flexibility, and ease of installation. Despite these advantages, the performance of such units can be significantly affected by external environmental conditions and changes in load demand. As a result, the unit frequently operates under non-standard conditions, which may lead to reduced lifespan and increased failure risks, especially for the compressor. This paper explores the root causes of compressor failures in real-world applications and provides actionable solutions to mitigate these issues.
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**2. Symptoms of Compressor Failure**
Compressors in air source heat pumps typically use fully enclosed piston designs, which are prone to failure under certain operating conditions. Common symptoms include:
- **(1) Suction and discharge valve rupture:**
The oil level is normal, but the valves are damaged. Bearings, crankshaft, and connecting rods remain intact.
- **(2) Compressor stall (most common):**
Oil appears black, with signs of bearing wear, cracked connecting rods, and friction marks on the crankshaft and bearings. Valves remain undamaged.
- **(3) Motor burnout:**
Insulation resistance drops to zero, while mechanical components like bearings, crankshaft, and connecting rods are undamaged.
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**3. Causes of Compressor Failure**
A detailed analysis of the above failures reveals several key causes:
**(1) Valve rupture due to liquid hammer**
This occurs when water enters the compressor due to a ruptured water-side system. For example, during cooling mode, if the flow switch fails or is manually bypassed, water in the heat exchanger may freeze, leading to pipe cracking and refrigerant-water mixing. Similarly, in winter, improper shutdown procedures can cause freezing and subsequent damage.
**(2) Compressor stall due to poor lubrication**
Poor lubrication often results from refrigerant dilution or oil being mixed with liquid refrigerant. Long periods of inactivity allow refrigerant to accumulate in the compressor, dissolving into the oil and reducing its effectiveness. This leads to inadequate lubrication and eventual stalling. Additionally, insufficient preheating before startup can exacerbate this issue.
**(3) Motor burnout**
While refrigerant backflow is a contributing factor, motor burnout can also result from overheating due to poor ventilation or contamination in the refrigeration system. If the motor is not properly cooled, especially in cold weather, it can overheat and eventually fail.
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**4. Improvement Measures**
To address the above issues and improve system reliability, the following measures are recommended:
- **Implement anti-freeze control:** Ensure that the water system is protected during shutdowns by using pumps or electric heaters when temperatures drop below a certain threshold.
- **Install drainage systems:** When the unit is not in use for long periods, drain the water from the heat exchanger to prevent freezing.
- **Avoid bypassing safety switches:** Ensure that flow switches and protection devices function correctly to avoid abnormal operation.
- **Improve preheating protocols:** Enhance the electronic control program to ensure sufficient crankcase heating before startup.
- **Optimize defrosting mechanisms:** Improve the defrosting process to prevent excessive refrigerant return and reduce the risk of compressor damage.
- **Refine system design:** Properly match expansion valves and gas-liquid separators, especially in low-temperature environments, to minimize refrigerant backflow.
- **Ensure clean refrigeration systems:** Maintain high-quality manufacturing and regular maintenance to prevent impurities and moisture from entering the system.
- **Train users:** Provide proper training for users on operation, maintenance, and troubleshooting to reduce human error and prolong system life.
By implementing these improvements, the operational stability and longevity of air source heat pump units can be significantly enhanced, reducing the occurrence of costly and disruptive compressor failures.
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