This month’s problem piece of equipment is a soda vending machine that has basically the same refrigeration system as a standard household refrigerator in which a standard capillary tube metering device is used to feed the evaporator. The other “refrigerator” similarities are a fan-cooled condenser and a forced-air evaporator. Figure 1 shows you an illustration of the evaporator section of the system (top) and the condenser section located in the lower part of the cabinet.

The complaint from the customer, who has positioned the unit outside their small motel, is that while the soda seems to be properly cooled during the middle of the day, there are times when the product is warmer than desired. Temperatures during the day are in the mid 70s, while the temperature later in the day drops to the low 40s. When you make your initial stop early in the afternoon, you note that the unit seems to be operating normally with both the evaporator and condenser fan motor running normally. And, when you check the wiring diagram, you note the condenser fan wiring shown in the partial diagram in Figure 2.

Since your initial check of the equipment shows no problems, you decide to schedule a second trip back to further evaluate the situation after the outside temperature has dropped. When you return during the low-ambient situation, you note that both the evaporator and condenser fan motor are again operating normally.

Your troubleshooting question: What is the next step you need to take to resolve the cooling problem with this equipment?

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Publication date: 09/07/2009