Some refrigeration systems are designed to be installed using a pre-charged line set. This normally allows for quicker installation and reduces the risk of non-condensables entering the system, saving both time and money on a typical installation.

These line sets use a quick connect coupling assembly, which allows refrigerant to be trapped in the tubing with the line set connected and then released by simply tightening a nut. However, using this type of line set is not without complications, and if installed incorrectly, it can lead to some major issues.

One of the first steps when using this line set is to verify that the refrigerant in the line set matches the refrigerant in the condensing unit and evaporator. Mixing refrigerants would be a serious mistake.

Recently, I installed a new walk-in cooler and freezer for a major fast food chain, and the system was designed for R-448A. Before I even started the installation, I verified the line set shipped was pre-charged with R-448A.

When connecting the line set to both the evaporator and condensing unit, it is very important to properly connect the coupling assembly. Failure to properly secure the couplings can lead to a leaking connection and/or refrigerant restriction. Do not rush this part of the installation. A failed connection will likely cost more time and material to correct than if a standard line set were used.

To ensure an unobstructed leak-free connection, follow these general guidelines:

• Do not remove the caps and plugs from the couplings until you are ready to connect them to the respective components. This will help prevent any damage to the threads as you run your line sets to the condensing unit and evaporator;
• When you are ready to connect, remove the protector caps and plugs and wipe the seats and threaded surfaces with a clean cloth to remove any possible foreign matter;
• Lubricate the threads, o-rings, diaphragms, and all internal coupling surfaces with refrigerant oil;
• Position the fittings on the correct connections and begin to tighten the couplings together by hand until it is certain that the threads are properly engaged. If you cannot engage the threads by hand at first, reposition the fittings and try again. Do not use a wrench to try and force the threads to engage because you will likely cross-thread the fitting and prevent it from sealing properly, resulting in a leaking connection. You may also lose the refrigerant in the system and be forced to cut out the fitting and replace it with a traditional coupling, evacuate the system, and replace the lost refrigerant; and
• Use two wrenches: one to rotate the swivel nut and one to hold the tubing in place. As the coupling is tightened, the diaphragms in the quick connect couplings will begin to be pierced. As that happens, there will be increased resistance to tightening the swivel nut. Continue tightening the swivel nut until it bottoms and no threads are showing. Then tighten the coupling nut an additional one-quarter turn. The final one-quarter turn forces two shoulders on the swivel nut end into the beveled surface of the male end, resulting in a sealed brass-to-brass connection. Do not overtighten.

Using a pre-charged line set can save time and money on an installation. However, when this process isn’t followed and they are improperly connected, they can make the installation process unnecessarily frustrating and costly.

Publication date: 7/2/2018

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