Heat Recovery Circuit Switching Failure → Waste Heat Loss

Question

Accepted Answer

4-way switchover solenoid valve (HR valve) coil burned out. Check: unable to switch circuit when heat recovery mode is requested What to do: Measure HR solenoid valve coil resistance (normal 15–30 Ω): replace coil or valve if burned Insufficient cooling water flow through heat recovery heat exchanger (desuperheater). Check: flow switch failed or pump stopped What to do: Check cooling water flow: verify heat exchanger inlet/outlet temperature difference (normal 5–8 °C); if flow is low, check pump and piping blockages Controller heat recovery interlock conditions not met. Check: compressor discharge temperature or demand signal not fed in What to do: Force-activate HR mode from controller service menu: output HR solenoid ON → listen for valve click Refrigerant leak in HR circuit causing pressure imbalance. Check: solenoid valve cannot open What to do: Check HR circuit for leaks with low-side gauge: after shutdown and equalization, HR line and main line pressures must match Demand signal wire break from heat recovery load (hot water tank, AHU preheat, etc.). Check: controller always stays in non-recovery mode What to do: Continuity test on demand signal wiring: confirm resistance ≤1 kΩ

Heat Recovery Circuit Switching Failure → Waste Heat Loss

Likely causes

4-way switchover solenoid valve (HR valve) coil burned out

Insufficient cooling water flow through heat recovery heat exchanger (desuperheater)

Controller heat recovery interlock conditions not met

Refrigerant leak in HR circuit causing pressure imbalance

Demand signal wire break from heat recovery load (hot water tank, AHU preheat, etc.)

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