R-Pro › Field cases › Chillers

Screw Compressor Slide Valve Stuck (Partial Load Control Failure)

Likely causes

Oil contamination or degradation causing slide valve hydraulic cylinder malfunction

Check: Take oil sample: check if total acid number (TAN) >0.5 mgKOH/g or viscosity deviates >±10% from ISO VG 68. Brown discoloration or suspended particles require immediate replacement

What to do: Replace all oil (ISO VG 68 specified type). Replace oil filter simultaneously (every 2,000 hours). Disassemble and inspect hydraulic cylinder

Slide valve position sensor (potentiometer) failure

Check: Check valve position signal (0–10V) from controller — if voltage stays fixed while solenoid operates, potentiometer is stuck. Confirm by measuring resistance value

What to do: Replace potentiometer. After replacement, calibrate 0%/50%/75%/100% steps from controller

Solenoid coil burned out or air ingress

Check: Measure solenoid coil resistance — replace if deviation exceeds ±15% from rated. Run oil pump → manually toggle solenoid ON/OFF → if no position change, hydraulic issue

What to do: Replace solenoid coil. Purge air from oil system if air ingress is present

Field tip

Slide valve stuck at 50% gives only half cooling capacity. Solenoid manual test distinguishes hydraulic vs electrical cause within 5 minutes. After extended shutdown, circulate oil at 0% load for 10+ minutes before incrementally increasing load.

All 565 cases work offline in R-Pro, with error codes for 62 brands and P-T data for 108 refrigerants.

Open R-Pro →

Related cases