When I replaced my A/C compressor last spring I drained all the oil out of the old unit, and measured the amount. Drained the new compressor and measured the amount. Then added enough oil to make up the difference plus a oz or two as the old compressors front seal was leaking oil. After evac of the system I put in around 4.5 lbs of 134A (per Manual), started up the motor and A/C full blast and let it run adding a little freon at a time until the dash vent temps were down around 50 degrees. Outside temp that day was 74 degrees. Ended up with 5.4 lbs of freon in the system. This whole process took all afternoon, add a little and wait, add a little and check temp and pressures.
We run the dash air non stop unless its really cold outside, performed like a champ all year.
With these coaches all being built a bit different it would be very hard to tell how much freon each needs to perform the best for all coaches. A auto or pickup which are all built the same its easy to tell how much freon each takes.
