Soda vending machines dispense beverages to thirsty people. Because of their frequent use, they tend to need maintenance on a regular basis. According to VendingAdvantage.com (see References), the top problems that may require troubleshooting of a soda vending machine are the machine failing to vend goods, take dollar bills or cool.
Open the machine and make sure there are cans in it. If the machine sells out, it will obviously not vend. Another possibility is that there is a can jam. This will stop the machine from functioning. The only way to solve a can jam is to remove all of the cans in one column until you get to the can that is jammed. Pull out that can, then carefully reload the cans back into the column. Yet another possibility is that the machine owes a credit to someone who put money into a slot but failed to make a selection. Soda vending machines are programmed for only one selection at a time, so if someone inserted money and did not make a selection, the machine will not take any more money until someone else makes that selection.
This can happen because the machine has run out of change. The vending machine will just spit the dollar back out at the customer. Filling the machine with change will fix this issue. Another issue that can arise is a dollar-bill jam. If a dollar bill is stuck in the validator, you must open the machine and clear the path by taking the validator apart and removing the jammed bill. There is a screw holding the validator and the bill box in the soda vending machine. Remove the screw, then remove the validator and push the tab on the top of the bill box to release it. Grasp the box and remove it from its housing. You should now be able to remove the jammed bill, much as you would clear a paper jam in a printer. Replace the bill box by snapping it back in place, and replace the validator and the screw. Clean the validator before reassembling it.
Make sure the vending machine has power and that its thermostat is set to the correct temperature. The thermostat may be in one of a few places, but the most common is to the rear of the cabinet, under the can chute. Adjust the thermostat by turning it clockwise to make it colder. If the machine is working and the compressor runs but the cans are not getting cold, the thermostat has likely gone bad and needs replacing.