Selecting the Right Stub Connection for Replacement Compressors
Matching stub connections makes installs easier, while the wrong choice can add delays
CONNECTION CHECK: When ordering a replacement compressor, make sure it has the same stub connection as the compressor it’s replacing, as this will make for an easier installation.
Compressors are manufactured with several different types of stub connections. The most popular is a brazed stub connection; however, they can also use a Rotolock connection or a service valve with a bolted connection.
When ordering a replacement compressor, it is important to make sure that it has the same type of stub connections as the original, as this will make for an easier installation. Although it is possible to switch from one connection type to another, it will add time and materials to the repair. Generally, the bill of material (BOM) of the compressor will list this feature. When ordering a compressor, either make sure the BOM includes the right stub connections, or verify with your supplier that the stubs will match.
When using a brazed connection, be careful not to overheat the joint. The connection between the stub tube and the shell may be made with a silver brazing alloy which, if overheated during the brazing process, can be damaged. Generally, a torch flame should be used primarily on the refrigerant line, with only enough heat applied to the stub to ensure the brazing alloy flows into the joint.
Heat should be applied to both sides of the tube, and the flame should be moved continuously in a circular motion to distribute the heat evenly. If using the brazing alloy requires flux, only the male connection should be fluxed, and only enough flux should be used to adequately cover the surface. Excess flux can enter the system and cause future issues.
If the original compressor model is not available or no longer manufactured, you may need to use a compressor with stub connections of a different size or connections in slightly different locations. If you need to swage the tubing to make a connection, avoid swaging the stub connection, as it can be damaged during the process. It is best to swage the ACR tubing end instead.
Some fractional horsepower compressors have a steel stub for the discharge line connection. This will require using a brazing alloy of a higher silver content than you may typically use for a copper-to-copper joint. I typically check the discharge stub of these compressors with a magnet. If the magnet sticks, then I will use an alloy designed for a copper-to-steel joint.
Compressors with a RotoLock connection will use an O-ring to seal between the RotoLock and compressor stub. If you need to braze tubing to the RotoLock connection, always remove this O-ring before heating the RotoLock. Otherwise, the O-ring will be damaged during the brazing process. I normally remove the O-ring and then hand-tighten the RotoLock connection back into position and then braze the tubing to the connection. This allows me to get the connection in the right position. After the brazing is done and the valve has cooled down, I will reinstall the O-ring and tighten the connection.
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Some compressors will use a bolt-in service valve to connect the compressor to the system. When replacing these compressors, you may need to scrape off the old gasket between the compressor body and valve and replace it. Take care when removing this gasket, as you need to prevent any gasket material from getting into the valve or compressor. Placing a clean rag into the opening while scraping off the gasket will usually prevent this from happening.
Working with the various stub connections of a compressor is not overly difficult. Remembering some of the finer details will help with an easier and smoother installation.
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