Unless something has changed recently, you do not have to pay for an answer, and I like it that way. The only time you won't get an answer is if no one knows it or your description is unclear.
If your system was open as in air was free to circulate, there can be a corrosion problem from the moisture in that air, but that's why we pump it into a vacuum first to boil the water out. Flushing is more important when the receiver drier comes apart and lets the desiccant circulate. That can plug the expansion valve. Otherwise flushing is not commonly done.
The important thing when retrofitting is to get the old oil out. When we first started doing these, we were told we needed different hoses with nylon liners because the R134 molecules were smaller and could leak out easier. The compressor had to be replaced because we needed higher pressures to get the needed efficiency. The new hoses could handle those pressures. Nothing was said about the condenser handling those higher pressures. Eventually we figured out all those new parts weren't needed. When I retrofitted my '88 Grand Caravan, all I did was unbolt the compressor so I could turn it over to drain the oil, and screwed on the adapter ports, evacuated the system and filled it up. We no longer replace hoses or compressors. System efficiency isn't a problem because it still goes by temperature in the evaporator, not pressure. If the temperature isn't low enough, the expansion valve just lets more refrigerant in. I didn't even worry about the residual oil in the rear evaporator and hoses. I just filled the compressor with the new oil and let 'er rip. Worked very nicely.
Sunday, June 5th, 2011 AT 9:36 PM