[TigerOats]

If we examine the concept of using a rad in a freezer then we have the following heat pathway - coolant to rad wall to air to evaporator wall to refrigerant. The bad part is the air. Again we come back to the fact that air is a bad conductor of heat. In any cooling design the ideal scenario is to get the heat to the transfer medium as fast as possible with the minimum of thermal interfaces. If you are using a refrigerant then then the ideal is to get the heat from the source to the refrigerant as quickly as possible.
I checked a website on home appliances and the fridge is the household item with the longest lifespan with an average lifespan of 14 years. On average with normal use a compressor works about 8 hours a day. In my current system the compressor works about 12 hours a day. This would equate to knocking off roughly a quarter of its expected lifespan. Compressors in a domestic situation are expected and designed to work in some fairly harsh conditions. In this context there is little or no danger of the motor burning out when used within the specified tolerances. The additional factor is that compressors would like most systems of their type suffer their greatest wear on startup because of a lack of lubrication on the wall of the chamber. So in this context they are more likely to suffer greater wear in the normal environment than in this application because their cycle time is shorter.
A/C units are generally bigger because they have to move a greater mass of refrigerant than a fridge. They would not be more or less prone to failure in my opinion.