The system is designed to be charged based on refrigerant WEIGHT. How do you plan on doing that with gauges???? The specs are rather tight on this....

If your comp has failed and contaminated the system, you will need to flush/clean- otherwise you will kill the new comp in short order.

Last time I had a failed evap (so no contamination) I just changed it and took it to a shop I knwo- he was nice enough to do a pump down/leak test- then recharged to the right amount. Fine since. (This was on a 2001 MDX about 3 years ago)