How My Garage Refrigerator Died :-(

My garage refrigerator was a life saver. We needed more space for frozen foods, and more capacity. I found it on Craig's List. I went back and fourth with the owners by email, and decided that I should go check it out. It was in great shape, so I bought it for $75.

We used it for probably 5 years before we had any real issue with it, other than a condenser fan motor failing. I rigged it with a 120mm high volume computer fan until I could get a new condenser motor. However, one fine day, the coil iced up. So the freezer side was not getting cold enough.

The defrost system on these older mechanical refrigerators is relatively simple.

Looking at the diagram you can see how the bi-metallic thermal switch controls the defrost system (it's on the upper right of the pic). It's a glorified temperature switch, sometimes called a defrost thermostat. In some commercial systems they call it a "defrost delay timer." That's confusing because it's not a literal timer. What it does is stop the defrost cycle if the freezer side is too hot or not cold enough. The reason they call it a defrost delay timer, is because it won't allow the defrost timer to cycle until the freezer is cold enough to require defrosting. That way you aren't heating the coil with the defrost heater -- adding heat before the freezer has pulled the temp down. It needs to be "cold enough" before defrost should work.

Because the defrost thermostat failed the defrost timer would never run. So, the refrigerator's evaporator coil was icing up. Here's a picture of what the temp switch looks like.

The defrost thermostat was cheap, less than $10 on Amazon.

When I took the old one off I immediately saw what was wrong. The assembly had leaked, and water infiltrated it. The entire thing was corroded inside. The wires going into it both just broke off.

I replaced the defrost thermostat and I replaced the defrost timer as well, just in case. But that might be where I got burned. Here's a picture of the timer. It has a little motor in it that runs it. This is beneficial because the motor generates just a little heat, keeping the unit from becoming wet inside.

Here you can see what went wrong with this defrost timer. Notice that the markings on the shaft line up with the marks on the housing. That means it's in defrost mode. This activates the defrost heater, and disables the refrigerator's compressor.

This is where things went drastically wrong. With the timer stopped in the defrost position, the refrigerator's compressor will not be allowed to start, causing the whole thing to eventually heat up. However, the defrost thermostat should stop the defrost heater from running, once the coil temperature is too high. BUT IT DIDN'T.

The result was completely nasty. The refrigerator's defrost heater just kept on chugging, heating the freezer side so much that it turned my frozen shrimp, which were white, red! It cooked the frozen shrimp in the package. Milk on the refrigerator side was all chunky. The smell could knock you down. It was a sad sight, because I lost a few hundred dollars worth of food.

Here's a picture of what the refrigerator's evaporator fan housing should look like.

Here's what I saw when I took it apart.

Needless to say, it was a perfect storm. Not only did the new defrost timer fail, but the defrost thermostat failed as well -- in the closed position. If I would have left the original defrost timer in place, this never would have happened. because I never turn the refrigerator off the failed closed defrost thermostat wouldn't really hurt anything.

Normally things like mechanical defrost timers work for 15+ years, but not these newer parts. They're just not like they used to be.

I even took apart the defrost timer to see if it appeared to be damaged, jammed or whatever. Nothing appeared to be wrong with it, and I checked the motor with an ohm meter, it appeared to be OK too. I'm not really sure why it failed.

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