Why is it unnecessary to change compressor oil periodically?

[ICanHas]

Car manufacturers still call for replacement of fluid not subject to external contamination such as automatic transmission and differential fluids.

Why is it necessary for these fluids to be changed, but not A/C compressor oil either auto or stationary?

You have to replace engine oil since it gets contaminated by combustion product. That's obvious.

[lynn comstock]

Oxygen and water are not present in a correctly installed and maintained refrigeration system. When they are present chemical reactions can and do damage the oil. This is not true for oils used in automotive applications.

Excessive temperature...above 300 *F can also damage the oil, but that temperature is never reached unless there is a design or mechanical flaw. Engine oil inescapably sees temperatures high enough in the combustion chamber to carbonize the oil. Thus the solution is to filter the oil and periodically replace it.

[Stamas]

Installed properly the inside of the system is a perfect climate for oil and does not get contaminated or breakdown like a combustion engine, barring failures of some kind.

[mrpogo]

I was taught that oil does not wear out it gets dirty,absorbs water and the additives flash off under the high heat loads of an internal combustion engine. In the Navy they don't replace oil in Main Reduction Gears ( big transmission that drives the propeller shaft). They just send it through a lube oil purifier that cleans the oil by centrifugal force. Which seperates the dirt and moisture from the oil. The only make up oil added to these systems is when there has been a leak.
In a refrigeration system the oil is never subjected to extremely high temps and the by products of combustion. There is no need to change the oil unless the system has to be opened for some reason in which case it absorbs moisture from the air.

[Mr Bill]

I use the high dollar A/C Delco filter driers on my installs.

[timebuilder]

Just to be clear, transmission fluid is one of the most abused fluids by its operating environment. Heat, contamination by clutches, bands, sprags, bearings, and converter lockup clutches makes changing it a necessity. It is amazing it lasts as long as it does!

[beenthere]

Its a sealed system, so no outside contaminates get into it.

[Joe Harper]

Plus customers would want you to do in 15 mins or less..

[y7turbo]

Just like everyone else said,

Less heat
No byproducts of combustion
no moisture.

[gasoilair]

Plus customers would want you to do in 15 mins or less..

Yeah for 29 bucks.