General Description

The top signals in the diagram represent the state of the three switches controlled by the cams attached to the dispenser motors on the coke machine. The bottom signal represents the power being applied to one side of the purchase relay.

The bottom two switches (Bypass and Cam Hold) are mechanically coupled. All three switches are controlled by a single rotating cam attached to the soda-dispensing motor.

We begin by assuming that the user has entered 40 cents and the money counter has just tripped the purchase relay to put the machine in a state where pressing a button will cause a soda to drop.

Details

1. The machine is in a purchase-ready state (the purchase relay is tripped, that is, it is in its NO position) but the user has not yet selected a frosty beverage. In this state, AC-common is being provided to all of the coke-selector switches from line Y10 on the purchase relay through the entire collection of cam-hold switches (bottom switch on the wiring diagram). The top switch (motor drive switch) provides power to hold the purchase relay in the "purchase enabled" state.
2. The user presses a button, thus routing AC-common power to the corresponding bin-empty switches and, assuming the bin in question is not empty, the power then flows to what in the diagram is the left side of the motor. The right side of the motor is always AC-hot, so the motor begins to turn.
3. The lower two switches flip from their NO positions to NC. This redirects AC-common away from the soda-select buttons on the front of the machine such that no other bin can be selected and results in the bottom (cam hold) switch providing AC-common to the motor. The middle switch (bypass switch) does nothing in this state and the top switch (motor drive) still holds the purchase relay.
4. The top (motor drive) switch flips to its NO position so that now both it and the bottom (cam hold) switch are providing power to the motor. In this position, the top switch no longer holds the purchase relay, so it flips back to its NC state.
5. Now that the purchase relay is disabled, and there is another source of power for the motor (top switch) the cam hold relay can re-enable the soda-select buttons, so it flips back to NO along with the bypass switch which then re-enables the hold line on the purchase relay (but the relay is in its NC state, so the hold line is not actually doing anything).
6. The top relay (motor drive) flips back to NC so that the top two switches are powering the (currently unused) relay hold line. There is no more power to the motor, so activity stops. This is the original state except that the purchase enable relay is in the NC position instead of NO.