Refrigerant travels around a sealed loop over and over, so a system that’s low on charge has a hole in it somewhere. Adding refrigerant without fixing that gets the box cold again for a while. Then it slowly warms back up, and you’re paying for another charge, and on an older R-22 system that refrigerant isn’t cheap.
Signs you might have a leak
Most leaks are slow. Over a few weeks the box runs a little warmer in the afternoon and the compressor runs longer before it shuts off. A freezer that used to sit well below 0 F may start having trouble getting there. On systems with a sight glass on the liquid line, you may see bubbles in it. Odd frost patterns are another clue, like the first few rows of the evaporator coil frosting while the rest stays bare.
Oil gives leaks away too. Refrigerant carries a little compressor oil around with it, so a leaking fitting often has a dark, oily, dusty patch around it. If you spot one on the copper lines near your condensing unit, mention it when you call.
How the leak gets found
The tech starts with an electronic leak detector and works along the places leaks usually show up. Bubble solution confirms a suspect spot. Some leaks are too small to find that way, or the system is nearly empty, and then the remaining refrigerant may be recovered so the system can be filled with dry nitrogen at a higher pressure and checked section by section. The usual suspects are flare fittings and the little valve cores on service ports, which can loosen with vibration over time. Small copper lines that rub against a cabinet or against each other will eventually wear through. And evaporator coils can develop pinhole leaks from corrosion, which is hard to see and often means the coil needs replacing. Display cases have a lot of tubing in tight spaces, so case repairs often turn into leak hunts.
Fixing it, then charging it
Depending on what’s found, the fix might be tightening or replacing a fitting, brazing a line, swapping a valve core or replacing a coil. After the repair the system is pressure tested to make sure it holds. Then it’s pulled into a vacuum to clear out air and moisture before it gets the right charge. The repair is priced in writing before it starts, and the service report afterward says where the leak was.
Any refrigerant that comes out of your system is recovered into a cylinder. It’s never vented.
If the leak is in the evaporator coil of an older system, it’s worth asking whether the money should go toward replacing the system. A low charge also makes compressors run hot, so if yours has been short on refrigerant for a while, the tech will check on the compressor while they’re there. Regular maintenance visits include a look for oily fittings, which is how a lot of slow leaks get caught early.
