Carrier 69NT40--541--200 TO 299, Операция и обслуживание

Страница: 70 / 112

6-4 T--317
b. The recommended method to evacuate and dehy-
drate the system is to connect three evacuation
hoses (see Figure 6-4) to the vacuum pump and
refrigeration unit. Be sure the service hoses are
suited for evacuation purposes.
c. Test the evacuation setup for leaks by backseating
the unit service valves and drawing a deep vacuum
with the vacuum pump and gauge valves open. Shut
off the pump and check to see if the vacuum holds.
Repair leaks if necessary.
d. Midseat the refrigerant system service valves.
e. Open the vacuum pump and electronic vacuum
gauge valves, if they are not already open. Start the
vacuum pump. Evacuate unit until the electronic vac-
uum gauge indicates 2000 microns. Close the elec-
tronic vacuum gauge and vacuum pump valves. Shut
off the vacuum pump. Wait a few minutes to be sure
the vacuum holds.
f. Break the vacuum with clean dry refrigerant 134a
gas. Raise system pressure to approximately 0.2 kg/
cm
@
(2 psig), monitoring it with the compound gauge.
g. Remove refrigerant using a refrigerant recovery sys-
tem.
h. Repeat steps e.and f. one time.
i. Remove the copper tubing and change the filter-drier.
Evacuate unit to 500 microns. Close the electronic
vacuum gauge and vacuum pump valves. Shut off the
vacuum pump. Wait five minutes to see if vacuum
holds. This procedure checks for residual moisture
and/or leaks.
j. With a vacuum still in the unit, the refrigerant charge
may be drawn into the system from a refrigerant con-
tainer on weight scales. Continue to paragraph 6.7
6.7 REFRIGERANT CHARGE
6.7.1 Checking the Refrigerant Charge
NOTE
To avoid damage to the earth’s ozone layer, use
a refrigerant recovery system whenever remov-
ing refrigerant. When working with refrigerants
you must comply with all local government envi-
ronmental laws. In the U.S.A., refer to EPA sec-
tion 608.
a. Connect the gauge manifold to the line piercing
valves. For units operating on a water cooled con-
denser, change over to air cooled operation.
b. Bring the container temperature to approximately
1.7
_
C (35
_
F) or --17.8
_
C (0
_
F). Then set the control-
ler set point to --25
_
C (--13
_
F) to ensure that the suc-
tion modulation valve is at maximum allowed open
position.
c. Partially block the condenser coil inlet air. Increase
the area blocked until the compressor discharge
pressure is raised to approximately 12 kg/cm
@
(175
psig).
d. On units equipped with a receiver, the level should be
between the glasses. On units equipped with a water
cooled condenser, the level should be at the center of
the glass. If the refrigerant level is not correct, contin-
ue with the following paragraphs to add or remove re-
frigerant as required.
6.7.2 Adding Refrigerant to System (Full Charge)
a. Evacuate unit and leave in deep vacuum. (Refer to
paragraph 6.6.)
b. Place cylinder of R-134a on scale and connect charg-
ing line from cylinder to liquid line process tube. Purge
charging line at liquid line valve and then note weight
of cylinder and refrigerant.
c. Open liquid valve on cylinder. Open liquid line valve
half-way and allow the liquid refrigerant to flow into
the unit until the correct weight of refrigerant (refer to
paragraph 2.2) has been added as indicated by
scales.
NOTE
It may be necessary to finish charging unit
through suction service valve in gas form, due
to pressure rise in high side of the system.
(Refer to section paragraph 6.7.3)
d. Backseat manual liquid line valve (to close off gauge
port). Close liquid valve on cylinder.
e. Start unit in cooling mode. Run approximately 10 min-
utes and check the refrigerant charge.
6.7.3 Adding Refrigerant to System (Partial
Charge)
a. Examine the unit refrigerant system for any evidence
of leaks. Repair as necessary. (Refer to paragraph
6.5.)
b. Maintain the conditions outlined in paragraph 6.7.1
c. Fully backseat the manifold gauge port
d. Connect charging line between the suction line pro-
cess tube and the cylinder of refrigerant R-134a.
Open VAPOR valve.
e. Partially frontseat (turn clockwise) the manifold
gauge valve and slowly add charge until the refriger-
ant appears at the proper level .
6.7.4 Emergency Shipboard Refrigerant Charging
Procedure
If the unit is not maintaining set point, refer to section 5
for possible causes. If the unit is then determined to be
low on refrigerant charge, follow the steps below.
a. Perform step 6.7.1.a.
b. If the unit is operating on water-cooled condenser
switch to air-cooled condenser operation.
c. If set point is in a perishable range, temporarily
lower the unit set point to ensure that the SMV is
fully open for this procedure.