This is the most profitable misunderstanding in our trade and the easiest one to explain. Refrigerant is not fuel.
Somebody rings us most weeks to book a gas top up as routine maintenance, the way you would book an oil change. It is worth explaining why that idea is wrong, because it costs people real money.
An air conditioner is a sealed system. The refrigerant inside it goes round and round changing state; it is not burnt, not consumed and not used up. A unit installed correctly and never touched will hold the same charge for fifteen years. So if your unit is low on refrigerant, there is precisely one reason: it is escaping somewhere.
Which means a top up is not a repair. It is a way of restoring cooling for a few months while the same hole keeps leaking, and it is the most common thing sold in this trade. At around 900 rufiyaa a time, twice a year, on a unit worth nine thousand, you can spend a third of the price of a new machine on gas in two years and own nothing at the end of it. We met a family in Hulhumalé last year who had done exactly that, four times, through three different companies, and not one of those companies had said the word leak.
Finding a leak takes an hour that nobody wants to pay for. We pressure the system with nitrogen, which is inert and cheap, and leave it on a gauge. If the needle moves, there is a leak and its size tells you roughly where to look. Then it is soap solution on the joints, or an electronic detector on the coil, and nine times out of ten in this country it is the outdoor coil, corroded from the outside by salt, usually at a bracket.
Then comes the decision, and it is the customer's rather than ours. A coil is repairable if the leak is in an accessible pipe, and not repairable in any way we would stand behind if it is in the fins. New coil, or new unit. We give both prices and the age of the machine and let people choose.
There is one more technical point that matters for anything bought in the last few years. Nearly every new unit sold here runs on R32, and R32 cannot sensibly be topped up. The correct procedure is to recover what is left, repair, evacuate under vacuum and recharge to the weight stamped on the nameplate. Adding a bit to a partly leaked charge gives you a unit that cools worse than before while the customer is charged for gas. If somebody offers to top up your R32 unit, they are either cutting a corner or they do not know.
The short version. Gas is not a service item. If you have paid for it twice, ask for the leak test instead.