Date registered: Jul 2010
Vehicle: 1995 C220
Location: Missouri, USA
Mentioned: 4 Post(s)
Quoted: 216 Post(s)
I'm going to say that 90% of shops do not do a flush of the system. But on the other hand, most aftermarket compressor companies will not honor the warranty on the compressor if you do not flush the system.
I think determining on whether to flush or not depends on why you are changing it to begin with. If it is a matter of the clutch failing, or the seals leaking on the compressor, I would say a flush is unnecessary. If the compressor failed internally(like locked up) then I would recommend flushing all lines, the evaporator, and replace the expansion valve and the condenser, and the dryer.
After that it is also important to put the correct amount of oil in the system, which depends on whether you flushed the system or not. If you flushed it, you need to put the manufacturers recommended amount of oil in the system. If you did not, you only need to put in what the old compressor had in it. Which means, you have to pour the old oil out of the old system and measure it, then pour the new oil out of the new compressor and save it, then put back the amount that you poured out of the old compressor. Then you should do no less than a 30-60 minute vacuum, then charge.
Hope that makes sense.
Also just a diy tip; when putting the ac fittings back together, replace the orings, and lubricate them with some ac system oil. This will keep them from tearing when you put them together, and the ac oil will not contaminate the system vs using some other lube.