Service manual

8−15
62-11389
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18
1. Refrigerant
Cylinder
2. Refrigerant
Recovery Unit
3. Manifold Gauge
Set
4. Valve
5. Vacuum Indicator
6. Vacuum Pump
7. Discharge Service
Valve
8. Compressor
9. Heat Exchanger
10. Evaporator
11. Electronic
Expansion Valve
12. Receiver
13. Liquid Line Service
Valve
14. Subcooler
15. Filter-Drier
16 Condenser
17 Suction Service
Valve
18 Compressor
Suction
Modulation Valve
(CSMV)
Figure 8−18 Refrigerant System
Service Equipment
8.6.2 Servicing The Refrigerant Charge
Servicing of the refrigerant charge includes: checking
the charge level, checking for noncondensibles,
removing the charge, pumping down the low side,
pumping down the compressor, adjusting the charge
level and adding a complete charge. Procedures for
charge service are provided in the following sub
paragraphs.
a. Checking Charge Level
Check the refrigerant charge before adding any
refrigerant to the system. Only add refrigerant if charge
is low. If charge is low, leak checking must be performed
(Refer to Section 8.6.3) and all leaks repaired before
adding refrigerant.
1. Install a manifold gauge set to allow reading of dis-
charge pressure. See Figure 8−18.
2. Start unit in Continuous Run Operation. Adjust set
point so that unit is running in high speed, fully loaded
and operating in cooling. Run approximately ten min-
utes - until the refrigeration system is warmed up and
the refrigerated compartment temperature is ap-
proaching set point.
3. Partially block off air flow to condenser coil so dis-
charge pressure rises to 230 psig (15.7 bar).
4. Check the receiver sight glasses to determine
charge. The system is correctly charged when the
lower sight glass is not empty and the upper sight
glass is not full.
5. If the system appears to be overcharged or under
charged, adjust charge. Refer to following step f.
b. Checking For Noncondensibles
To check for noncondensibles, proceed as follows:
1. Install a manifold gauge set to allow reading of suction
and discharge pressure. See Figure 8−18.
2. Stabilize system to equalize pressure between the
suction and discharge side of the system. The refri-
gerant system needs to be off for several hours.
3. Measure temperature at the copper tubing leaving
the condenser (not the subcooler).
4. Record compressor discharge pressure.
5. Determine saturation pressure as it corresponds to
the condenser temperature using the temperature
pressure chart, Table 8−7.
6. If gauge reading is not close to the calculated satura-
tion pressure in step 5, noncondensibles or mixed re-
frigerants are present.
7. Remove refrigerant. Refer to following step c.
8. Leak check, evacuate and recharge the system.
c. Removing Charge
To remove the refrigerant charge, proceed as follows:
1. If the system is in operating condition, it will be quicker
to remove the charge by continuing with step 2. If the
system is not in operating condition, skip steps 2
through 5 and continue with step 6.
2 Install a manifold gauge set to allow reading of suction
and discharge pressure. See Figure 8−18.
CAUTION
Only a refrigerant cylinder that has previ-
ously been used with R404A should be con-
nected to this refrigeration unit.
3. Connect a clean, evacuated refrigerant cylinder to the
liquid line service valve connection. Place the cylinder
on a weight scale so the refrigerant going into the cyl-
inder can be monitored.
4. Start the unit and run in high speed cool. Cover the
condenser to raise the discharge pressure to as high
as 375 psig (25.5 bar). Do not let the discharge pres-
sure exceed 400 psig (27.2 bar). Open the refrigerant
cylinder valve, and allow the refrigerant to flow into