About eight years ago, I installed a liquid line filter in the a/c compressor output line in my 1990 745 to prevent any potential compressor failure debris from migrating through the a/c system. This filter is an aluminum can that is installed into the line using compression fittings. At the time, I thought that my then twelve year old compressor might be the weak link in the system. Wrong.

Last week, the a/c failed. We opened it up to find that the filter had failed: the filter medium had itself migrated down to the orifice valve, plugging it and causing an overpressure condition that in in turn caused the compressor front seal to blow out. So the device designed to prevent system damage itself caused a significant amount of it.
I still believe in liquid line filters, but now will install only removable, replaceable units. Autoacsystems.com has one such unit:

http://www.autoacsystems.com/fasttrack/filterinstruction1.html

While you still have to evacuate the system to replace it, that is not that big a deal.
Anybody else have such experiences?
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See the 700/900 FAQ at the drop-down menu above right.