Inlet valve & blowdown solenoid service
Rebuild the load/unload inlet valve and verify the blowdown circuit — the two parts behind most load-cycling and hot-restart complaints.
This guide is general field reference for trained, qualified service technicians. It is not a substitute for the original equipment manufacturer's service manual, applicable codes (NEC, OSHA, ASME, local), or the judgment of a licensed professional. Procedures, torque values, pressures, refrigerants, and safety requirements vary by make, model, jurisdiction, and revision. Always verify against current OEM documentation and follow your employer's safety program. Working on compressed-air, electrical, pressure-vessel, and refrigerant systems can cause serious injury or death. By using this guide you accept all risk; AirCompDX and its authors disclaim all warranties and are not liable for any damage, injury, loss, or code violation arising from its use.
The inlet valve is spring-loaded and can snap closed on fingers. Depressurize the control air line and the sump before removing the actuator cover.
- Socket and hex key set
- Multimeter for solenoid coil checks
- Soapy water for leak testing
- Pick set for O-rings
- Inlet valve rebuild kit (piston seal, shaft O-rings, poppet disc, spring)
- Blowdown solenoid valve or coil
- Control air tubing and fittings
- Air inlet filter element
- 1Confirm symptoms
Fails to unload → stuck-open inlet valve or dead solenoid. Fails to load → stuck-closed valve or no control air. Hard hot restart → blowdown not venting the sump within 30–60 s of unload.
- 2Check the solenoid electrically
Measure coil resistance and verify control voltage at the coil when the controller commands unload. A coil that reads open or a rectifier that reads shorted is a five-minute fix.
- 3Check the solenoid pneumatically
With control voltage applied, feel for air passing. Solenoid valves plug with varnish from degraded fluid — carbon in the port means the fluid needs attention too.
- 4Remove and disassemble the inlet valve
LOTO, depressurize, remove the air filter housing, then the valve. Photograph the assembly order before disassembly; poppet-and-plate designs vary widely between OEMs.
- 5Rebuild
Replace the piston seal, shaft O-rings, and poppet disc. Inspect the bore for scoring — a scored actuator bore leaks control air and makes the valve modulate erratically.
- 6Check the modulating orifice
On modulating (turn-valve) packages, verify the metering orifice is clear. A partially blocked orifice makes the machine hunt between load and unload.
- 7Reinstall and set
New inlet filter, reinstall the valve, reconnect control air, verify no leaks with soapy water at pressure.
- 8Verify cycling
Run the machine through several load/unload cycles. Confirm full load current at load, unloaded current dropping to roughly 25–35% of full load, and sump venting below 20 psi during extended unload.