17
M
INI
-S
PACE
EC I
NSTALLATION
, O
PERATION
AND
M
AINTENANCE
M
ANUAL
refrigerant may need to be added or removed when fi ne tuning
the charge to obtain the correct superheat and sub-cooling
temperatures.
Example: Estimate the amount of refrigerant required for
a refrigeration circuit in a system using R410A refrigerant
consisting of a CCD-041-A-EC unit connected with a 1/2” x 30
foot liquid line and 5/8” x 30 foot discharge line to a STULZ
Model SCS-018 condenser.
A/C Unit
= 3.8 lbs
+1/2” Liquid Line- 30 × (5.88 /100)
= 1.764 lbs
+ 5/8” Discharge Line- 30 × (2.03/100) = 0.609 lbs
+ Condenser
= 0.5 lbs
Estimated Refrigerant Charge
= 6.673 lbs
(Round off to nearest 0.1 lb
= 6.7 lbs)
2.9.4.1
Preparing the System For Charging
1. With all the system piping connections made, perform a
dry nitrogen leak detection test on the system. Using dry
nitrogen only, pressurize the system to 150 psig. Ensure
all service and solenoid valves are energized open and
that no part of the system is isolated from the pressurized
nitrogen.
2. Since there is no refrigerant in the system to detect at
this point, leaks may be detected by observing if there’s
been a change in the standing pressure after 12 hours.
A signifi cant drop in pressure (>10 psig) indicates a leak
in the system that needs to be repaired. After the system
is determined to be free of leaks, you may evacuate the
system.
2.9.4.2 Evacuate
the
System
CAUTION
A proper vacuum must be drawn on the refrigerant
system to remove moisture before charging. If this
is not done, the refrigerant charge will combine with
moisture in the pipes to form an acid that will eventually
lead to compressor failure. A triple evacuation
procedure with dry nitrogen is recommended,
especially for systems with newly installed refrigerant
piping.
NOTE
Use a vacuum pump capable of evacuating the
entire volume of the A/C system, including newly
installed or existing piping. The pump must be in good
operating condition. Ensure it contains clean, fresh
oil. Manufacturers recommend you change the oil in
the pump regularly to maintain its ability to remove
moisture.
CAUTION
PVE oil is used in systems with R410A refrigerant.
PVE oil quickly absorbs moisture when exposed
to air. Acid forms in systems with high PVE oil
moisture levels (via reaction between moisture and
refrigerant), resulting in system contamination. Keep
the entire system sealed as much as possible and
minimize exposure of PVE oil to outside air.
R410A systems operate at high pressures, which must be
considered when checking the operating temperatures/
pressures while charging or troubleshooting the system.
Tables are provided in Section 2.11.1 on page 21 showing
the temperature/pressure characteristics for R410A.
2.9.4 Estimating Refrigerant Charge
When charging a system with R410A refrigerant it will
be necessary to weigh in the refrigerant and confi rm the
charge is correct by checking the superheat and sub-cooling
temperatures (see Section 2.9.4.3 on page 18).
You can estimate the amount of refrigerant needed by adding
the amount of refrigerant required for the A/C unit (3.8 lbs for
all CC()-()-A-EC units) plus the condenser (see Table 4) plus
the interconnecting refrigerant piping between the A/C unit
and the condenser (see Table 5). The values in the tables are
the estimated weights for the refrigerant circuit.
Table 4 shows the estimated charge weights for STULZ model
SCS condensers. Depending upon site specifi c conditions,
SCS Model
Number
R410A Charge
(less receiver)
R410A Charge
(with receiver)
SCS-018
0.5 lbs
2.6 lbs
SCS-024
1.0 lbs
5.2 lbs
SCS-036
1.5 lbs
7.8 lbs
SCS-060
2.2 lbs
11.7 lbs
SCS-MC-015
0.8 lbs
4.0 lbs
SCS-MC-018
1.0 lbs
4.2 lbs
Line Size
O.D.
Liquid Line
Discharge
Line
1/2”
5.88 lbs
1.27 lbs
5/8”
9.44 lbs
2.03 lbs
7/8”
19.62 lbs
4.22 lbs
Table 4.
Estimated Refrigerant Charge Weight
for STULZ SCS Condensers
Table 5.
Weight of R410A Refrigerant
(lbs/100 ft of type L tubing)
