Faced to the coming phase-out (note) of R-404A, tests carried out by their technical service on R-404A/R-407F mixtures showed no loss of performance, or compatibility issues compared to pure R-404A.
The group has therefore decided when necessary to top up R-407F in existing R-404A systems, which provides significant advantages in terms of time and costs, avoiding the lengthy process of recovering 300-400 kg R-404A and disposing of it.
Except in the US where mixing refrigerants is forbidden, the process is generally accepted, with the only requirements of changing the nameplate and updating the logbook with the added quantities of R-407F.
NB : Regulation 517 014 summary From 1 January 2020, ban of servicing existing refrigeration equipment with a charge size over 40 tonnes of CO2 equivalent (i.e. 10.2 kg R-404A) with HFC of GWP >2500.
Source : Cooling Post