R-Pro › Field cases › Freezers & ultra-low temperature
Cascade system: high stage runs but low stage does not start (no cooling at all)
Likely causes
Low-stage compressor relay failure (most common cause)
Check: With the high stage running, check the low-stage relay coil voltage and contact continuity. No contact closure = bad relay.
What to do: Replace the relay. Suspect the pressure control as well — the maker's service hint is to jump out the pressure switch at the control board to isolate the cause (diagnosis only; always restore it afterwards).
🚨 In a cascade system the high stage must run first and cool the cascade heat exchanger before the low stage starts. Running the low stage without the high stage sends low-stage discharge pressure through the roof and kills the compressor. When the low stage will not run, confirm the high stage is running normally before touching low-stage parts.
All 565 cases work offline in R-Pro, with error codes for 62 brands and P-T data for 108 refrigerants.
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