Controversial subject amongst refrigeration techs. Viking has made it almost impossible to get service information on their machines but here's where you are; R410B Hot Shot is a direct replacement for R134a. Unless your R134A system is still under manufacturers warranty. There is a temperature difference and might throw off the thermistors so using it will void the warranty. Your problem is too many cooks in the kitchen. Pick your favorite cook. Sounds like the commercial guy owes you one, and tell him your system has a restriction, probably from moisture, at the drier or cap tube. Cut the filter/drier out and replace it with a quality replacement. Vacuum it down to 29imvg and flash charge it with R410B hot shot. Recover it then vacuum the system again. When the vacuum is at 29 let the vacuum pump run an additional 20 minutes. Add the correct charge and adjust to 5 LB with gauges. It operates at a little higher pressure than R134a. If you have a tech that knows what he's doing, you shouldn't have any problems with Hot Shot.

This isn't something you can do. You need to have a certified refrigeration tech do it. Didn't you already pay someone to do this repair. His repair went south doesn't he guaranty his work?

If you've had refrigeration experience and your brazing skills are half decent, you can do it. These are the filters I use. Cut the cap tube back.

Viking built in refers come with a 6 year full sealed system warranty and a 12 yr parts only sealed system warranty...

Hot Shot will void that warranty. Have someone recover all hot shot from the unit and re-charge with 134a. Then call your authorized servicer maybe one now who doesn't know hotshot was used.

I'm completely neutral on using hot shot, but why not just charge with 134a? I'm assuming your commercial guy just didn't have a bottle on his truck? The debate is that the different chemicals used to produce hot shot will wear on the compressor seals differently than 134a. At least that's what most manufacturers will claim.

-16 on the evap but 40 in the upper area of the freezer sound less like sealed system issue and more like an evaporator fan issue, or restriction in the ducting running along the back wall.

-you stated that the suction line was frozen. If the suction line is frosted near the compressor the unit is over charged. If the suction line at the evap is what's iced up it's undercharged (leak).

My best suggestion...Recover all refrigerant, run in a deep vacuum 600 microns if a micron gauge is available, and let it run in that vacuum for at least 20 minutes as stated before. If you struggle to get below 1200-1500 microns there is probably a leak in the system. It will have to be located and repaired. Once vacuumed down to satisfaction install a filter drier that is designed for contaminated systems. I once had to change one of these driers twice after following up someone who used a dye to locate a leak. The dye may have never hurt anything, but wasn't allowed by the manufacturer. gas up the unit and let it run a day or so, then recover and start all over. Vacuum down for extended time, then install a new drier (oem), charge to spec. Let the unit run for 24 hours, the evaporator should have a light but even frost covering the fins. This will indicate that the refrigerant is moving freely and the charge is correct and cooling should occur.

If there are still issues, they are probably not sealed system related. All of this should be done by someone familiar with the unit. I hear it often that time of service led to hiring someone who is completely unfamiliar with the unit. It is usually better to wait for the quality servicer for that product that have someone shotgun it like what it sounds like happened here.

It should tell you on the model tag