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Length
Feet
5
10
15
20
25
30
50
75
100
150
FOR EXAMPLE:
Calculate the Preliminary Charge for a ZF13 compressor with a 25 ft. liquid line, ½" ODS Copper
Rated Tons of Capacity (From Table 4) = 1.15
Amount of Refrigerant to Fill a 1/2" ODS Liquid Line, 25 ft. long (From Table 5) = 1.67 lbs.
Preliminary Charge = (Rated Tons of Refrigeration x 3 lbs of R-449A) + (Liquid Line Refrigerant
Volume)
Preliminary Charge = (1.15 x 3) + 1.67 = 5.12 lbs (This value is also given in Table 6 below)
2. Weigh in the preliminary charge from Calculations, or from Table 6
3.
Be sure all service valves are "open".
4.
Start the system by "flipping on" the disconnect on the side of the electrical box.
5.
Check evaporator fan motors after start-up. Medium temperature, air defrost fans run
continuously (the cooler) , low temperature fans provided with electric defrost (the
freezer) will be delayed by the fan control.
6. During pulldown, expect evaporator superheat to be high, as the box is under a very high load.
As the room temperature approaches set point, the superheat will begin to drop, and begin to
approach the superheat setpoint, designated in the controller programming, typically 10⁰F.
Continue to let the box temperature fall. This is a good opportunity to calibrate the adjustable low
pressure controller. Recommended set points are as follows:
Cut Out = 2 psig
7. When the box temperature approached set point, this is the time test the defrost cycle.
The reaction of the compressor during a defrost cycle is a good time to determine if the system is
charged properly. The following sequence will likely be seen if the charge is not correct.
IF SHORT CYCLING ON THE LOW-PRESSURE CONTROL AT THE BEGINNING OF THE DEFROST,
THE SYSTEM IS UNDERCHARGED.
Table 5
Lbs. of R-449A to fill Liquid line by Length
Liquid Line Size (in.ODS)
3/8"
1/2"
0.18
0.34
0.36
0.67
0.54
1.00
0.72
1.34
0.9
1.67
1.08
2.00
1.8
3.35
2.7
5.01
3.6
6.7
5.4
10.1
Cut-In = 20 psig
5/8"
0.54
1.08
1.62
2.16
2.7
3.24
5.4
8.1
10.8
16.2
13
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