Lay It On The Line Sets

By Barbara A. Checket-Hanks

It's a fact. Any number of service problems can be prevented if technicians take proper care when installing new line sets on replacement heat pumps or new installations.

According to the trainers at York UPG, "Many service problems can be avoided by taking adequate precautions to provide an internally clean and dry system, and by using procedures and materials that conform to established standards." However, this is just one consideration among many when it comes to installing line sets correctly.

Think Before You Install

Planning is critical when it comes to installing line sets for optimum efficiency, serviceability, and homeowner satisfaction.

Whether it's a factory line set or field-fabricated tubing for that new heat pump system, the pros from the UPG training department want you to make sure that the lines are installed so that they will not obstruct service access to the indoor coil, air-handling system, or filter. Such obstructions can impede proper service and maintenance later.

Figure 1. Recommended construction of oil traps.

Moreover, take care to install the lines with as few bends as possible. "Care must be taken not to damage the couplings or kink the tubing," recommend the trainers. Also, by isolating the refrigerant lines, you will help minimize noise traveling from the equipment to the home.

"Never solder vapor and liquid lines together," they warn. If you need to, tape them together for convenience sake and for support; but make sure they are completely insulated from each other. Support them at appropriate intervals with suitable hangers and brackets. In particular, do not allow metal-to-metal contact.

When it comes to elbows, use long-radius types whenever possible, the trainers pointed out - except when you are fabricating oil return traps. These require short-radius elbows in order to minimize the volume of oil returning to the compressor. (See Figure 1.)

Going Underground

Installing contractors should use PVC piping "as a conduit for all underground installations," the trainers state. Keep buried lines as short as possible; this helps minimize the buildup of liquid refrigerant in the vapor line during long periods of shutdown.

Wherever refrigerant lines penetrate a wall, the company recommends packing the area with fiberglass insulation and a sealing material (i.e., permagum). This helps reduce vibration as well as retaining some flexibility.

"Insulate all vapor lines with a minimum of 1/2 inch of foam rubber," the company recommends. "Liquid lines that will be exposed to direct sunlight also need to be insulated."

If you need to fabricate your own piping in the field:

Use hard-drawn "L"-type copper tubing if there will be no significant bending around pipes or other obstructions. "If soft copper must be used," the trainers add, "care should be taken to avoid sharp bends which may cause a restriction."

Braze all copper-to-copper joints with Silfos-5 brazing material (or equivalent). Do not use soft solder.

While you are brazing, flow nitrogen through the system to prevent scaling and contamination.

Table 1. Equivalent lengths of elbows. (*Two 45-degree-radius ells equals one 90-degree-radius ell.)

Line Lengths

There are many important considerations for line lengths and sizing for heat pump systems. We will touch on just a few of the more important ones mentioned by the UPG trainers. (For more information, contact a reputable source of unitary installation particulars, such as the manufacturer.)

According to this manufacturer, "The total length of interconnecting tubing is the sum of all horizontal and vertical runs from the indoor unit to the outdoor unit." For heat pumps, the limiting factor is the accumulator's storage capacity.

"Total equivalent line lengths must only be used when calculating pressure drop," states UPG. Therefore, use the information in Table 1 to calculate equivalent lengths for elbows.

Elevation differences between the indoor and outdoor units can cause performance and reliability problems, the trainers say, "if special considerations are not given to line sizes and orifice sizes."

For split-system heat pumps, interconnecting refrigerant lines need to be sized so that they match the manufacturer's factory-supplied fittings. Vapor lines may be increased by one size to minimize pressure drop; however, liquid lines should never be increased or decreased, the manufacturer says. "The additional charge required for larger liquid lines will overflow the accumulator in the heating cycle."

Publication date: 05/17/2004

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