Refrigerant Piping Lines

The refrigerant in an air conditioning system or air conditioner is transported to the different components in it through copper piping of small diameter called refrigerant lines. The line that carries liquid refrigerant from the condenser or receiver to a pressure reducing device is called the liquid line. Between the evaporator and the compressor inlet, the line is called the suction line.

The suction line carries the refrigerant in vapor form to the compressor where it is compressed into a higher pressure in order to create a flow of refrigerant in the system. Therefore, the sizing of the suction line is critical to creating the proper pressure drop for the system. A suction line needs to be able to return oil from the evaporator to the compressor under minimum load conditions.

Additionally, the suction line should be designed to prevent drainage of oil into a non-operational from an operating one, and to prevent the drainage of liquid into a compressor that is shut down.
In a remote or split air conditioner system, the suction line’s slope also becomes important. If the evaporator coil is at a higher elevation than the condensing unit, the slope of the suction line should have a continuous fall of ¼ inch per foot towards the condensing unit. When the evaporator coil is higher than the condensing unit and excess line has coils in it, then the coils must be oriented horizontally such that the refrigerant flows from the top of the coil to the bottom towards the condenser unit continuously, in other words, with no coils slanting up in the flow.

Refrigerant Piping Tips

During routine maintenance, one of the things that is checked is if the liquid line and suction line are not in contact with each other; if there is direct contact between the two, then heat will transfer to the suction line.

Refrigerant line connections should also be checked at the evaporator coil for seating correctly. This connection is for a non-reusable valve which requires 100 percent seating; if not seated 100%, the metal diaphragm will obstruct the line, thus restricting refrigerant flow. To achieve the proper seating, the connection’s nut is tightened with one wrench while another wrench is used to hold the valve stationary fitting.

If ice or frost if forming on an expansion valve or capillary tube, then a hot wet cloth is applied to the tube or valve to melt the ice plugging it up inside. If the suction line is frosty, there may be an overcharge of refrigerant, the expansion valve may be stuck or the evaporator fan may need replacement.