R-Pro › Field cases › Components
4-Way Reversing Valve Slug — Heat Pump Mode Switching Failure
Likely causes
Oil sludge accumulation — slide piston seizure
Check: Confirm mode switching failure or incomplete switch; measure pilot solenoid coil resistance (∞=coil fault); verify differential pressure (discharge-suction ≥0.4 MPa required)
What to do: With compressor running, cycle reversing valve coil ON/OFF 5~6 times → tap valve body sidewall 3~5 times with rubber mallet → if no effect, replace full valve assembly (wrap with wet cloth during welding, inert gas purge mandatory)
Insufficient differential pressure (<0.3 MPa) — slug fails to shift
Check: Measure discharge-suction pressure with gauges during switching attempt — need ≥0.4 MPa; if low, suspect compressor performance degradation
What to do: Normalize compressor performance then retest; if liquid refrigerant flooding causes icing around slug, hot-gas defrost or replace valve; after replacement, change refrigeration oil and replace filter-drier
When replacing the reversing valve, wrap the valve body with a wet cloth to prevent internal seal damage from welding heat. Prevention: run heat pump mode test at least once a year.
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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