In Part 2 of the Rack Refrigeration Class at Kalos Services, Matthew Taylor discusses safeties, service, and more. Part 1 focuses more on the basic refrigeration circuit of a rack refrigeration system.

When safeties are piped together, we have to keep in mind that they're a bit more complex than most HVAC refrigeration systems, especially when it comes to the oil side. All of these safeties and their proper installation can be located on the wiring diagrams. Safeties often respond to pressure, both in the refrigerant circuit and the oil circuit, but they may also respond to amperage or temperature.

Each compressor on a rack has its own safety controls, but all compressor safeties should be wired in series. Overloads may measure temperature or amperage and break the circuit if it detects unsafe conditions. We also deploy demand cooling strategies to cool the compressor and help control compression ratios. We can also control capacity with staging strategies. Mechanical controls may be able to communicate with electronic controllers, but these cases are less common in conventional rack systems.

Matthew also covers:

• Pop-offs and high-pressure switches
• Overloads and misdiagnosed compressor failures
• Sentronic oil pressure controls
• Mechanical and electronic controls
• Adjusting metering devices
• Liquid and vapor injection
• Subcooling and interstage cooling
• Suction filters and when to use them
• Service valves, hoses, and depressing Schrader cores for checking charge
• Restrictions in the refrigerant circuit
• Accumulators
• Pressure transducers and troubleshooting
• Mechanical and electronic time delays
• Bypassing safeties in mission-critical applications
• Compressor staging and unloaders

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