Heatcraft Refrigeration Products H-IM-FL1A, Installating And Operation Manual

8

Liquid Lines 

Liquid lines should be sized for a minimum pressure drop to 

prevent “flashing”. Flashing in the liquid lines would create 

additional pressure drop and poor expansion valve operation. 

If a system requires long liquid lines from the receiver to the 

evaporator or if the liquid has to rise vertically upward any 

distance, the losses should be calculated to determine whether 

or not a heat exchanger is required. The use of a suction 

to liquid heat exchanger may be used to subcool the liquid 

to prevent flashing. This method of subcooling will normally 

provide no more than 20

˚

F subcooling on high pressure 

systems. The amount of subcooling will depend on the design 

and size of the heat exchanger and on the operating suction 

and discharge pressures. An additional benefit from the use 

of the suction to liquid type heat exchanger is that it can 

help raise the superheat in the suction line to prevent liquid 

return to the compressor via the suction line. Generally, heat 

exchangers are not recommended on R-22 low temperature 

systems. However, they have proved necessary on short, 

well insulated suction line runs to provide superheat at the 

compressor.

Figure 6. Suction P-Traps.

Slope 1/4" 

per 10 ft. 

toward 

compressor

Suction Lines

NOTE:  If the suction line must rise to a point  

higher than the suction connection on the 

evaporator, a suction line trap at the outlet 

of the evaporator must be provided. 

Horizontal suction lines should slope away from the evaporator 

toward the compressor at the rate of 1/4 inch per 10 feet for 

good oil return. When multiple evaporators are connected in 

series using a common suction line, the branch suction lines 

must enter the top of the common suction line. 
For dual or multiple evaporator systems, the branch lines to 

each evaporator should be sized for the evaporator capacity. 

The main common line should be sized for the total system 

capacity.
Suction lines that are outside of refrigerated space must be 

insulated. See the 

Line Insulation

 section on page 11 for more 

information.

Suction Line Risers

Prefabricated wrought copper traps are available, or a trap can 

be made by using two street ells and one regular ell. The suction 

trap must be the same size as the suction line. For long vertical 

risers, additional traps may be necessary. Generally, one trap is 

recommended for each length of pipe (approximately 20 feet) to 

insure proper oil movement. See Figure 6 below for methods of 

constructing proper suction line P-traps.