Introduction to Commercial Refrigeration Systems : Compressor and Fan Motor Failures

 Overview:

• Systems can fail due to incorrect component usage, component wear over time, or failure caused by another component.
• Proper diagnosis requires understanding the system's operation.

Common Service Call:

• Symptom: Space is not cooling properly.

Diagnosing Motor Failures:

1. Fan Motor Failures:

   • Evaporator Fan:
     • If the evaporator fan stops working, the coil won't absorb heat, leading to low evaporator temperature and pressure.
     • May cause excessive frost on the evaporator coil.
   • Condenser Fan:
     • If the condenser fan stops working, condensing temperature and pressure rise, causing the compressor to work harder and consume more power.
     • May result in the compressor cycling off on a high-pressure safety switch or overload protector.

2. Compressor Failures:

   • Electrical Issues:
     • Inspect electrical connections and test windings (check for open, shorted, or grounded windings).
     • Contactor relay, safety switches, and overloads may also be sources of problems.
   • Mechanical Issues:
     • Liquid Slugging: Caused by liquid floodback, refrigerant overcharge, or a defective expansion valve. Liquid enters the compressor without boiling off, causing mechanical damage.
     • Flooded Starts: Occur when refrigerant vapor migrates to the compressor oil during the off cycle and condenses. Upon startup, the pressure drop causes the liquid to boil and erupt from the oil, leading to mechanical damage.
     • Overheating: Can be caused by a lack of lubrication, the wrong lubricant, or a high compression ratio, leading to higher than normal discharge temperatures. This is more common in low-temperature systems with high compression ratios.