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 thermo vacuum valve port. See Fig 1 .
- Blow air into main control air port and then into air cleaner port. Check that air flow is blocked at both ports.
- Using a vacuum pump, apply 7.9 in. Hg to thermo vacuum valve port. 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.