Question: When should the system be flushed?
Answer: We believe if the a/c system is opened for service, it's a good time to flush. A clean system minimizes the chance of a comeback. On systems that utilize an orifice tube, you can usually judge the condition by looking at the inlet side of the orifice tube screen. If a substantial amount of debris is found, flushing would be recommended. Likewise, visual inspection of the refrigerant oil may indicate it's time to flush.
Question: When I flush my system, can the compressor be flushed too?
Answer: No, not with typical solvent flush methods. The compressor should be removed from the vehicle and the oil drained from it. You can pour refrigerant oil into the suction port and turn the compressor hub by hand which will pump clean oil through the compressor. Remember, compressors don't compress liquids. So, make sure you rotate the compressor hub by hand enough to ensure you don't liquid "slug" the compressor.
Question: Can the Accumulator or Filter Drier be flushed?
Answer: No. Since these are filters which contain desiccant, they are considered normal replacement items.
Question: Can I flush the hoses and lines?
Answer: If you're sure the solvent that you are using will not harm rubber or nylon, then it's alright to flush the hoses. Just make sure that you don't flush trough any hoses that have mufflers built into them. And also make sure you don't attempt to flush through the compressor or expansion device.
Question: I noticed my A/C hoses have mufflers. Can those be flushed?
Answer: Though many technicians will flush through hose mufflers, it's usually not considered a good idea. As a general rule, hoses with mufflers should be replaced instead of flushed. Since the muffler is only used to reduce noise, some people opt to remove the muffler in order to salvage the hose.
Question: Can I flush through the Orifice tube or expansion valve?
Answer: No. Flushing through the orifice tube or expansion valve is too restrictive to the flow of solvent. There is one exception of course. On some Ford models the orifice tube cannot be removed without cutting the liquid line. We know of technicians who often remove the liquid line and back flush through it. In theory, back flushing the liquid line will clean the orifice tube. This is said to work in most cases; though replacing the liquid line is the preferred method. Remember, a dirty orifice tube can starve a compressor of oil.
Question: Should the evaporator be flushed?
Answer: Most would say yes, but some would argue that it's not worth the extra effort for two reasons. Flush solvents can be very difficult to remove from some evaporators. Sometimes the risk of not being able to remove the solvent outweighs the benefit of flushing that component. Secondly, some would point out that evaporators stay fairly clean because any dirt floating around the system is captured first by the receiver drier, then by the inlet screen of the expansion valve. In the case of an orifice tube system, most debris would be caught by the orifice tube screens before it could reach the evaporator. While this is mostly true, systems that use the block style expansion valves have no inlet screen, and dirt from a ruptured receiver drier could find its way into the evaporator. Also, oil likes to accumulate in low-lying areas of the evaporator. If your goal of flushing is to remove dirty oil, you'll have plenty of it in your evaporator.