On the bottom of the stack there is a microswitch that engages after the vend solenoid triggers the lockout flapper which then prevents additional coins from being inserted into the coin mechanism. There might be a different name for it.
For the info of the OP, I have a vend switch, but the "arm" to actuale it is broke/missing. So the previous owner just shorted the two leads to the switch together which now keeps the CREMs pulled in all the time (all that means is you can put in more coins after the initial purchase but before you pull out the drink). I left them shorted otherwise i'd have the same issue you have.
See my thread on it...
http://soda-machines.com/discussions/index.php/topic,19475.0.html
