Different refrigerants?

[tradesite]

I was asked to look at repairing the cellar cooling for a pub customer of mine. They had two cellar cooling units, one that had broken down years before and one that had been installed about 4 years ago. The newer one turned out to have a knackered compressor. To cut a long story short, I managed to get the original unit going and is running great. What I would like to ask is this: the original unit runs on R404 and the newer unit runs on R134a, both were installed to do exactly the same job to the same cellar, both are hermetic compressors and are physically about the same size. I know that the R404 has higher pressures than the R134a, so when choosing a unit to do the exact same job why the difference in the refrigerant and is any one refrigerant ,for these particular types of applications, any better than another.
Please excuse my ignorance on this subject as I only normally do domestic fridges and smaller bottle coolers etc, but I like to learn!
Another question whilst I am on the subject am I right in saying that it is difficult to gas charge the system with R404 via the suction side of the compressor and it is easier to initially charge it with liquid on the high side or have I got it completely wrong?

Regards.

Nigel.

[bowral fridgy]

By cellar are you are meaning a cold-room with a forced draft evaporator or a beer chilling system using a flooded evaporator ie Temprites ? The later won't work with zeotropic blends such as 404A due to temperature glide. If running a FDC the expansion valve must match the refrigerant otherwise you'll suffer floodback or starved evaporator. You generally get greater cooling capacity from same sized compressor using 404A but higher head pressure and susceptbility to flash gas in liquid line in high ambient conditions if condenser not up to task

[tradesite]

Thanks for your reply ! It is a cold room.