Mercury Repair Questions? Ask a Mechanic for Answers ASAP
The system controls air flow by operating a series of vacuum actuators (see attached graphic). In your case, either the switch on the control head is bad (most common cause), or the vacuum hoses are disconnected or some of the vacuum actuators are bad.
If you're skilled DIY'er who wants to tackle this issue yourself and have access to a hand-held vacuum pump, I'd be more than happy to guide you through the diagnostic procedure.