Cummins/Onan — Lock-Off Pressure Test (Low-Pressure LPG Demand Regulator)
Testing & diagnosis
From a Cummins/Onan service manual — check it applies to your exact model before use.
Applies to: Cummins/Onan HGJAA, Cummins/Onan HGJAB, Cummins/Onan HGJAC, Cummins/Onan HGJAD, Cummins/Onan HGJAE, Cummins/Onan HGJAF
Before you start
- Bench test: keep diaphragm in vertical plane to avoid erroneous readings
Procedure
- Connect regulator inlet to air pressure regulated to 11 in WC (28 cm).
- Disconnect hose from carburetor at regulator outlet.
- Tee two hoses to the regulator vent hose (3/8 in I.D.).
- Connect one hose to inclined manometer reading 0 to 2 in WC.
- Attach soap bubble to hose barb at regulator outlet.
- Blow lightly into pressurizing hose and read lock-off pressure.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Lock-off pressure 0.20 to 0.35 inches WC (5.1 to 8.9 mm)
- Replace regulator if out of range
Full service-parts list: Cummins/Onan HGJAA →, Cummins/Onan HGJAB →, Cummins/Onan HGJAC →, Cummins/Onan HGJAD →
Source: Cummins/Onan service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.