Are you EPA certified? (must have)
Do you know how to "tap into a system" and install a schrader valve for evacuation and charging?
There are a few ways to accomplish this; Use a "tap valve, or solder a schrader valve on the "process tube" It's a tube that is pinched off at the factory after the charge was weighed in. If the Tech is going to install 2 taps, one on low and one on high. then the tech may be planning of using gauges to charge it.. not the best way on small equipment. Name plate charge type and weight is almost always listed by the MFG.
Do you know how to weigh in refrigerant charges that are less then a pound? Domestic, RV, Marine, small units in general? ( Small systems generally should not be charged by gauge operating pressures) Yes, we all do try to charge by pressure or amps.. and many of us are good at it.. but we know what is "right" and if we don't want call backs we strive to "do it right"
(Charging cylinder works but electronic scales are most accurate.) Charging/Scales | TIF - An SPX Brand
If the service person says something like "I'll just give it a shot" I would not feel very confident in the answer
Are you familiar with small 12/24 volt systems used for marine/RV/solar/domestic?
(this is a big question) "everyone lies" re Dr house
Why did you love Freon 12 so much?
(Because the pressures were very close to the actual temperatures in the system)
What is low, med, high refrigeration?
without being too specific; Low= frozen foods, med = like your home refrigerator, High wine, flowers,
Of course there are hundreds of questions that could be asked. I only wanted to mention a few.
Air conditioning and heating people generally don't work on refrigeration, those that do; (or used to) like yours truly
have made it a point in their career to learn the differences in AC and Refrigeration equipment. and the unique differences in small systems.
"Marine" hvacr. is generally the same as the trade with certain differences, but realize. Not all boat systems are tiny like on most our sailboats where power is a important factor.
Passenger ships for example, have large.. very large systems, just like large high rise or sprawling buildings. Yet even on ships, you may find little dorm size refrigerators in the state rooms
the big difference in your systems is size, roughly if you don't have 120/240 volt 24/7 365 your going to most likely have 12/24volt power supplying your equipment.
Not many techs adapt their thinking to small systems. All the principals of mechanical refrigeration apply.. They are just small.. tiny even. 12 and 24 volt power supply is a mystery to many also.. was to me.. and still is, but! I do work at learning about the little 12volt wonders by Danfoss and a couple of other mfgs. that have cornered that market.
Troubleshooting, other then checking wiring, connections, and voltage. It's almost always all about power, the fan, the "module and circuit boards" on just about anything now a days.. those not with it in learning about the "circuit boards" fall behind those that make it a point to know about codes, read outs, thermistors, sensors. etc. Electronics invaded this trade just like automotive many many years ago.
"Just throw on the gauges and check the pressures" AHEM! just the hoses on the gauge set may hold more refrigerant then your unit! Please, please, don't assume the system needs "shot"! No, this is not a "how to" discussion. it's just to help those that feel they need the help from a person in the trade.
Small equipment .. any, mechanical refrigeration and ac system for that matter, should be evacuated with a "deep vacuum pump" (sometimes called "high vacuum" ) "purging" is a big NO on anything making temps below freezing.
You are allowed to ask questions. If you don't feel confidence in the answers (not to be confused with ego) call someone else!
(This is an attempt to help those not feeling qualified to try DIY I'm not in the marine trade and I'm not seeking business fixing marine hvacr systems)
Hope to helps!