Speed Control Operates But No Resume, Acceleration, or Coast

1. Check to ensure proper operation of SET-ACCEL, COAST, and RESUME switches and slip ring circuits. If satisfactory, proceed to step 2. If not satisfactory, service or replace switch and/or circuit as necessary.
2. Ensure that all system vacuum hoses are tightly connected and are free of cuts, cracks and kinks.
3. If vehicle symptoms involve acceleration or resume functions, proceed as follows:
a. Check all system vacuum lines for tight connections, cuts or kinks. Check that there is at least 2.5 inches Hg of vacuum supplied to servo. If vacuum is satisfactory, proceed to step b. If not satisfactory, service vacuum supply as needed.
b. Disconnect vacuum hose at servo end, then the vacuum reservoir line at check valve and plug open valve port. Apply 18 inches of vacuum to hose at servo end. If vacuum holds, proceed to step c. If vacuum does not hold, replace check valve and repeat step b.
c. Check that dump is closed when brake pedal is not depressed. Apply 18 inches of vacuum to dump valve. If vacuum can be pumped and held, proceed to step d. If vacuum cannot be pumped and held, replace or adjust valve as necessary.
d. Disconnect reservoir vacuum line at check valve, then apply 18 inches of vacuum to open end of line. If vacuum holds, proceed to step 4. If vacuum does not hold, proceed to step e.
e. Disconnect vacuum line from reservoir port and plug open end, then apply 18 inches of vacuum to other end of line disconnected from servo check valve. If vacuum holds, replace reservoir and repeat step c. If vacuum does not hold, replace reservoir vacuum line.
4. Perform servo tests. If tests are satisfactory, proceed to step 5. If tests are not satisfactory, replace servo.
5. Replace amplifier with known good amplifier. If system operation is satisfactory, replace amplifier. If system operation is still not satisfactory, ensure all system electrical connectors have proper contact.