Sealed system repairs have become increasing sophisticated since the days when I first picked up a pair of gauges. When I attended refrigeration school back in the early 70s we had no recovery machines, no charging cylinders. Charging a refrigeration system with a bathroom scale was considered high tech. Back then you could vent refrigerant into the corporal air without guilt, and because refrigerant was so inexpensive, we used it to blow out drains and condenser coils. Times have changed, but the skills necessary to make proper repairs haven’t. What’s changed are the rules and the equipment.
In this two part series, I will first cover the basic equipment recommended for servicing sealed systems and in part 2 we will address the technique and procedures.
The common types of failures that would make it necessary for you to enter into the sealed refrigerant system are:
Undercharge/overcharge of refrigerant
Restriction in the flow of refrigerant
You should be familiar with the correct diagnostic procedures that will pinpoint one of these problems. Always remember that there are many factors that can baffle your diagnosis of system failure. Some include:
Customer usage problems
Electrical and mechanical problems
KEYS TO SUCCESSFUL SEALED SYSTEM REPAIRS
Make a proper diagnosis of the problem
Use correct equipment that is properly maintained in the approved manner
Observe all safety precautions
Follow recommended procedures during the repair.
It is not only important that you have the correct equipment, but also that your equipment is in good working condition. Much of your sealed system tools will require periodic upkeep and maintenance.
The fastest and most thorough way to evacuate a sealed system is with a refrigerant recovery machine. The EPA has strict rules for removing and handling refrigerant. Help protect our environment. Do not release freon into the atmosphere. These machines are designed to draw out the refrigerant vapor and transfer it to a holding tank, and if the refrigerant is not contaminated, you can reuse it. Recovery machines come in many sizes, but for household refrigerators a compact unit will suffice. You cannot perform any sealed system repairs without first removing the refrigerant.
You’ll also need a recovery tank to store the recovered refrigerant. Recovery tanks come in various sizes. For household refrigerators you can get by with a small 2lb tank if you can find one. GE manufactured a small refrigerant tank that came with their refrigerant recovery machines years ago, but I haven’t been able to find one on the open market since, you may have to settle for a 30 lb tank. I still use the 2 lb tanks manufactured by GE because they take up less space and I can carry them in my tool bag. If you’re sure your sealed system isn’t contaminated, you can use your charging cylinder to hold the contents until it’s time for a recharge.
Domestic refrigerators are critically charged. That means they require an exact amount of refrigerant. Many years ago, before charging cylinders were available I used a bathroom scale, but it was a tedious process and took more time. Other methods, such as the frost-back method sufficed, but it could take hours before the system balanced out. Back then, if needed, you could vent an over-charged system into the corporal air. Times have changed, and they changed for the better because there’s no need to wait around anymore for pressures and temperatures to balance out. Now, we weigh the correct amount of refrigerant into the cylinder, transfer it into the system and presto, you’re done. No need to wait wondering if the unit is properly charged. Today’s charging cylinders are accurate to the oz. and are compact enough to fit in a tool case. I use a 16 oz. charging cylinder available from Thermal Engineering. What I like about this particular cylinder is the ability to rebuild it; a kit is obtainable from the manufacture to replace the seals and quartz-glass.
Vacuum pumps are standard equipment for any seriously minded technician. They’re rated in CFM’s (cubic feet minute) and are available in single-stage, two-stage, and for commercial and industrial applications, three-stage. I use a two-stage rotary pump capable of reducing pressure on average of 50 to 250 microns which, in most cases, will boil-off any moisture at room temperature. I also carry extra vacuum pump oil in my service vehicle and replace it after each use to prevent contamination. For a thorough understanding of how vacuum pumps work see Modern Refrigeration and Air Conditioning, GW Publishers.
If you are old fashioned like me then you’ll prefer using a jar of bubbles to find a leak or a halide leak detector which attaches to a propane or MC tank. Halide leak detectors are quite accurate and are not expensive and are still available from local suppliers. With that being said, modern technology has trumped again and now electronic leak detectors are out in the forefront. They are more accurate, readily available, compact and affordable and no sealed system technician can do without one simply because they save enormous amounts of time. There are several manufactures today with brand names you’ll recognize available from most supply houses specializing in refrigeration and electronic instruments.
Access valves, sometimes called line-tap valves, saddle valves, and piercing valves allow access into a sealed system in just a few minutes. In the 50s and 60s, GE and Frigidaire had special access ports attached to their compressors that required special tools. Up until the early 90s, Sub-Zero refrigerators came supplied with process ports, which allowed easy access. The GE and Sub-Zero ports were on the low-pressure side of the system while the Frigidaire’s were mounted on the high-side dome. They were helpful and saved the cost of installing a piercing valve. Today one of the most popular access valves on the market is manufactured by the Sealed Unit Parts Company (SUPCO). Their patented Bullet Piercing Valve comes in a variety of sizes including the most popular BP31, which is the most widely used in the domestic refrigeration field. They fit 1/4″, 5/16″, and 3/8″ tubing and are designed for permanent installation on the low-pressure side of the system.
For sweating and brazing you’ll need an acetylene tank. For space saving the MC tank is most suitable because it can fit into a tool box. When you’re pressed for space in a small vehicle like mine, it’s ideal. However, a B tank will suffice if you don’t mind the extra weight. Both B and MC tanks are refillable from local suppliers.
TORCH AND ACCESSORIES
For most sealed system repairs you’ll need several pieces of equipment including a torch, striker, cleaning brushes, swag and flaring tools and a ball-peen hammer. My torch of choice is the torbo-torch from Cyberweld which creates a hotter flame by using the oxygen in the air to mix with the flowing acetylene to produce enough heat to braze copper to steel. There are a variety of tips available to accommodate almost every size. For domestic refrigeration equipment I use a number 5 tip and a smaller number 3 tip for tubing smaller than 1/4″ , however, some manufactures have different heat ratings, so you may need to experiment. Ask your local supplier or someone in the trade. You’ll most likely get a variety of answers, but remember to limit the size of the flame as much as possible to avoid safety issues. A flame guard is also an additional piece of protection.
A pinch-off tool can be a helpful device for sealing-off the sealed system after a recharge. When it is necessary to tap into a system, if you have to remove the line-tap valve for any reason, you use the pinch-off tool to close off the process port. We’ll talk more on this in part 2. There are several types and styles of pinch-off tools to choose from. I personally prefer a tool with a ball end and a Tork handle.
A swaging tool makes joining tubing together quickly and less costly. You use them in conjunction with a flare-block. Each piece is machined to provide a snug fit from the male into the female end. In the long run, you’ll save on sweat-couplings and joints; less joints means less chances of a refrigerant leak in the future. I prefer individual sizes and use 1/8”, 1/4”, 5/16” and 3/8″. I’ll cover more on this topic in part 2, when we discuss procedures and safety.
I only carry a 2″ mini cutter because I very seldom work on units with larger than 3/8″ tubing. There are many brands to choose from, but carry an extra blade and occasionally tighten the set screw holding the cutter wheel in place. I’ve lost many cutter blades in my career.
BRAZING RODS/SILVER SOLDER/FLUX
Here is where preference becomes an issue. I like using silver solder with a 56% silver content. Sometimes, that’s not always available, so I settle for 45%. I like the flow better than brazing rods. However, some of my top technicians use the rods and claim superiority and reliability, with very few bounced jobs. It’s all in the technique. Like I said above, it’s a matter of preference. Be sure you use the appropriate flux for each type of solder. You’re supply house can recommend a matching brand.
Wire brushes, and sand cloth are essential in preparing any soldering task for leak-proof joints. There are also liquid chemicals that you brush on, liquid sandpaper as it is sometimes called, that eliminates the need to sand at all. I prefer sand cloth. I carry 1/4” and 3/8” brushes. A worn-down 3/8” brush can be used for 5/16” tubing.
If you’re going to be doing sealed system repairs you’ll need different sizes of copper tubing. The most popular sizes are the same sizes as your swag tools; 1/8”, 1/4”, 5/16”, and 3/8’. Copper tubing is not only measured in diameter (OD), but also wall thickness, usually .030, .032 for refrigeration systems in the HVAC industries. Don’t forget sweat couplings just in case you can’t swag. Copper tubing designed for ice makers and water supply lines are not recommended for refrigeration work.
I very rarely use flare nuts in my day-to-day service business because sweating and brazing are not only better, they’re quicker and less likely to leak. The constant expanding and contracting of refrigeration lines, because of temperature fluctuations, can work the joints loose over time and create an unnecessary callback. With that being said, I do carry some an assortment of different sizes in my tool box.
There are other helpful accessories you might consider carrying in your magic tool box, some of which are: extra flints for you striker, open-end wrenches for securing your pressure regulator-tip attachment, a jewelers saw and file, tubing benders and extra schrader valves.
In this first part series of sealed system repairs, we’ve covered the basics as far as tools and equipment is concerned. In the next segment, part 2, we’ll discuss the techniques and safety procedures to help you become a sealed system pro.