The deck lid should be closed during the entire filling procedure; otherwise you run the risk of a compressor failure or hose rupture. If you mix refrigerants you will have a difficult time getting a shop to work on your A/C system in the future. Some shops sample the A/C refrigerant to check for mixed refrigerants. If you manage to get it into a shop and contaminate their refrigerant recovery sytem expect to pay a hefty charge for it's cleaning/repair. I fully expect EPA to eventually ban the sale of R-134a and all other refrigerant substitutes to the general publc because of these provisional A/C repairs with the mixing of refrigerants.
Jim