If you haven't got up running and screaming reading this prose, I salute you because most customers would have sent me packing already. For those in the technical part of it, hopefully it helps or at least gives you reason to laugh. Either way, mission accomplished.
So the refrigerant, coolant, freon, etc is low. We can either add leak sealer and refrigerant and hope it stops the leak, or find and fix it. I'm not a big fan of leak sealers myself, but for a customer contemplating ruining a vacation or trying to defer the expense until next season, it's an alternative worth considering. Dump it in and pray that it hold is all I can say. Easy Seal brand seems to work the best for this, but I've also encountered several systems where the leak was too large.
The first thing to do is look for the obvious. Are the Schrader valves loose or damaged? There's usually two in the condensing unit and one in the indoor coil; these are common sources of leaks. Usually, you will hear the leaks or find them with bubbles at the the condensing unit. This is because hooking up and removing the hoses will result in a false positive with an electronic device. If you can't fix it tightening the cores, use a core removal tool that lets you replace them without recovering the charge and vacuuming the system. The one inside the indoor coil will need an electronic leak finder, such as the Bacharach Informant 2 to find as bubbles won't be very practical there. This is also good for finding smaller leaks anyway.
Another way to find leaks is visually and this means looking for oil on fittings or where someone didn't join two pieces correctly. Grab a couple wrenches and tighten all the fittings on mini splits and many indoor coils with compression fittings. Most of the time, these will cure a leak without having to take too much time and effort. However, if involves a poor joint, crack or other breach in the system, you will have to recover the refrigerant, fix the leak, charge it with nitrogen, vacuum and recharge.
Most of the time this involves using a torch and there's no substitute for an Oxy-Acetylene outfit. Propane and MAPP Gas will not get the fittings or filler metal hot enough to fill the joints and make the repair. I've had some success with low temperature brazing rod such as Harris' Blockade, but this stuff has a tendency to bubble when you try and heat it with a MAPP gas torch and has some issues with flowing. It is cheaper to use at about $15 a pack as opposed to $120 for silver brazing rod, but refrigerant is also pricey and most jobs only need less than one stick of the good stuff anyway. Bite the bullet and use it, because callbacks are a pain. Just heat up the base metal without melting it and apply the brazing rod to fill the leaks. If there's plumbing solder on the joints, just heating this stuff will remove it and then apply the silver brazing rod to it. Once you've found and fixed the leaks, let the joint cool and charge the system with nitrogen. Usually not a bad idea to have a light charge of it while you fix the leaks, but this is your call. If the charge doesn't drop, you've fixed all the leaks for now. Vacuum the system down and either weigh in the charge or by superheat or subcooling with the proper refrigerant.
To the customer, this isn't a walk in the park and the items we use to do the repair properly are not cheap either. Refrigerant is crazy expensive as of this writing. R410 costs about $260 for a 25 pound jug wholesale and over $400 for 25 pounds of R22. The latter is only going up and we could face shortages of it by summer's end. Blame the Montreal Protocol for this one. Soon R410 will be replaced because of its "global warming" potential (I can't make this horse feathers up) with carbon dioxide or good old CO2. It's $37,000 per day per violation for allowing "ozone depleting" refrigerants into the air, so we can't legally just dump R22 into a system without fixing it. Some firms will keep doing this until this stuff gets out of this world on price, but not forever. I personally believe that "global warming" "climate change" and "ozone depletion" are bunk, as someone is getting filthy rich over this planned obsolescence. However, it isn't me or the business owner that is. Every time there's a change, we have to invest in new equipment, materials and tools. I've spent close to $6000 in the past 3 years upgrading my tools and training to stay current and compliant. This doesn't include buying and replacing tools necessary at any rate. My boss has also had to upgrade and shell out more money too. Because the cost of everything from refrigerant to copper and aluminum to steel had gone up, this is not a cost a business owner can afford to absorb and still stay in business. It hasn't resulted in his pay going up at all, and though I can't complain, it hasn't booted my pay either. This is much like the clerk facing numerous customer tirades after gasoline prices spike. These guys and gals aren't getting rich either and most are barely getting by. Please understand the cost of the effort and materials when getting a quote for a job. Sure it's expensive, but it's even more expensive to do the job wrong or illegally. You wouldn't want us to do that. Maranatha!