Feedback Control

Ensure engine is at operating temperature. Connect vacuum control valve hose number 31 to air control B. See Fig 1 . Disconnect and plug vacuum hose number 14 from power valve. See Figure .

Fig 1: By-passing Vacuum Control Valve
Start engine and operate at 2500 RPM. Check for operation of frequency solenoids A and B. See Fig 2 .
NOTE: Operation of frequency solenoid valves may be determined by a repeated clicking noise, or touching each frequency solenoid valve by hand.
If both frequency solenoid valves are operating, go to step 6). If either frequency solenoid valve does not operate, replace it and retest. If both frequency solenoid valves do not operate, check for voltage at frequency solenoid valve connector with engine at 2500 RPM.
If voltage fluctuates between 12 and 0 volts, replace frequency solenoid valves and retest. If no volts are present, or 12 volts are present and engine runs poorly, go to Trouble Shooting.

Fig 2: View of Frequency Solenoid Valves
If 12 volts are available and engine operates normally, check condition of vacuum hoses. If no trouble is found, check operation of air control valves A and B, and constant vacuum valve.
Unplug and reconnect hoses removed in step 1). Turn A/C and all accessories off. Check to see if frequency solenoid valves A and B are operating. If not, system is okay.
If frequency solenoid valves are operating, go to Trouble Shooting. Reconnect hose number 31 to vacuum control valve. See Fig 1 .