R-Pro › Field cases › Components
Reciprocating Unloader Solenoid Stuck — Part-Load Capacity Control Failure
Likely causes
Solenoid coil burnout — DC resistance deviates from spec (20~80Ω)
Check: Measure solenoid coil DC resistance with multimeter (spec 20~80Ω). No 'click' when energized = plunger stuck. Verify supply voltage 24 VAC ±10%
What to do: Replace coil if faulty → if plunger stuck, disassemble and clean with cleaner or replace → replace unloader valve seat and O-ring with OEM kit → verify 50%/75%/100% load step switching by manual forced actuation
Insufficient oil pressure — unloader piston hydraulic actuation inadequate (below 0.15 MPa)
Check: Check oil pressure on unloader hydraulic line with gauge — minimum condition for unloader operation: above 0.2 MPa
What to do: Resolve oil pressure drop cause (check oil pump, strainer, oil level) → confirm oil level normal then re-measure oil pressure
Stuck unloader means always 100% full load → repeated overheating and overcurrent trips. When current log shows repetitive trip pattern, suspect unloader failure first.
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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