Glasco gvb50 slider ?s

hi all, i have a glasco gvb50 slider. i need to know how many volts should be at the plug where the interior fan motor plugs up inside the tank ? my fan is not working and i now have like 28 volts there. and the fan is real hard to turn. there is a switch inside the box that is pushed in when you close the lid. does that switch turn off the compressor or the interior fan or both ? it does not seem to do any thing now when the lid is open the compressor unit still runs. the box did not come with a thermostat. i straight wired it to test and it cools fast. i need to know what kind it takes. does it attach to the tube (contact type)or should i run one inside the box where the bottles are. i am new to soda boxes so any imput would be apreciated.

 thanks
 jesse patterson