Orbit 57020 Valve Zone 3 Won't Open Without Manual Bleed Adjustment

5-zone system, all Orbit 57020 valves. Zones 1,2,4,5 work. Zone 3 valve energizes but won't open unless bleed screw is opened until water leaks, then closed—every cycle. Solenoid, diaphragm, plunger, all internals replaced except valve body. Works only if bleed left partially open (wastes water).

Three Diagnostic Paths

1. Valve installation direction: "Make sure that the arrows point in the direction of water flow through the valve."
2. Plunger port debris: Shut off water, remove solenoid, push wire/paper clip up/down through round port hole to free debris. Ensure plunger and O-ring in place on reassembly.
3. Voltage/continuity testing: Valve needs ≥18 VAC. Check controller output (24-27 VAC consistent). Then ohm-test field wiring: controller to valve. ~30 ohms normal; 6-8 ohms = short. Disconnect at valve to isolate solenoid vs. wire short. Check wire resistance alone (couple ohms).

Since all internals are new and other zones work, the issue is likely a microscopic port blockage in the valve body or a wiring fault specific to zone 3.