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CO₂ Single Condensing Units: Relief Valves, pRack Pain, and Dorin Two‑Stage DiagnosticsBrett Wetzel and Kevin Compass open the Advanced Refrigeration Podcast joking about “pop” in the Midwest before diving into CO₂ single condensing units as Brett teaches in Minnesota and discusses an SCM Frigo unit. They compare common controllers (Carel pRack/mini PAC, Danfoss, and Copeland possibilities), complain about limited tech-friendly navigation and lack of onboard trending, and discuss pulling data via Modbus/BACnet and supervisory options like Boss Mini. Brett reviews relief valve piping after seeing popped reliefs, critiques tight packaging and reliability, and notes issues like overcharging and mismatched evaporator/valve capacity that can empty a sight glass. They walk through SCM Frigo medium-temp piping, internal heat exchange, Carel E2V-C valves, BGV function, and oil system designs, then cover a Dorin two-stage low-temp unit with floating flash tank pressure and shared plenum cooling. Brett demonstrates using Dorin software to estimate expected interstage/flash tank pressure, amperage, and temperatures to diagnose performance without relying on pump-down tests, and points to the web-based version of the tool.
