Federal 4WD Models
- Remove hoses from valve and mark for reinstallation. Blow air into valve through slow control air port and check that air flow is blocked at valve port to thermo vacuum valve. See Fig 1 .
- Blow air into main control air port and then into port to air cleaner. Check that air flow is blocked at both ports.
- Using a vacuum pump, apply 7.9-19.7 in. Hg to valve's port to thermo vacuum valve. With vacuum applied, seal main control air port with finger. Blow air into slow control air port and check that air flows freely through valve.
- With vacuum applied, open and blow into main control air port while sealing slow control air port with finger. Check that air flows freely through valve. Replace valve if it does not operate as outlined.