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Cascade unit: low running pressures on both sides (no cooling) — how to confirm a leak

Likely causes

Refrigerant leak (low running pressures on both sides is a clear indication)

Check: Shut the unit off and read the soaking (standing) pressures after 12 to 24 hours, then compare with the service manual values. Below spec confirms a leak.

What to do: Repair the leak, then restore per the maker: pressurise with 300 PSI (about 21 bar) dry nitrogen and hold at least 24 hours → if tight, evacuate; 50 microns recommended (200 microns or less acceptable) → hold vacuum 12 hours, then charge. If the compressor was replaced, replace the capillary assembly too and flush the system.

High suction pressure with low head pressure → oil restriction (low stage)

Check: Read both gauges together and confirm the high-suction / low-head combination. That combination usually means an oil restriction, though not always.

What to do: The maker's policy is a low-stage rebuild. 🚨 Flushing the system before reassembly is vital — skip it and the residual oil/debris brings the fault straight back.

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