Unless your system has debris in it from the compressor coming apart, or if the system has been open for an extended period, skip the flush. The evaporator doesn’t hold much oil, so I wouldn’t worry about flushing it just to remove oil.

How to Clean a Car’s AC Evaporator

1. Inspect your vehicle’s air conditioning system under the hood. You are looking for the evaporator/heater box assembly.
2. Access the evaporator core.
3. Spray the cleaner through the access point towards the evaporator core.
4. Lightly rinse the area with water.
5. Seal the heater box.

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.

How to Clean Air Conditioner Drain Line With Vinegar in 6 Steps | Drain Line Cleaning

1. Turn off your air conditioner.
2. Locate your condensate drain line.
3. Identify the access point on the drain line.
4. Flush with distilled vinegar.
5. Let the solution sit for 30 minutes.
6. Repeat each month.

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.

R22 refrigerant and its HFC replacement R410A are totally incompatible. Your existing condensing unit and cooling coil are not suited to the new higher pressure refrigerant. It is possible to reuse the copper tubing lineset between the two, but we will discuss that later.

As long as you properly remove all refrigerant and oil, it’s ok to reuse a line set that once held R-22 refrigerant.