4-- 6© 2012 Mobile Climate Control T-299 Rev. 08/2012
4.6.3 Procedure For Evacuation and Dehydrating
System (Triple Evacuation)
a. Remove all refrigerant using a refrigerant recovery
system (Refer to paragraph )
b. The recomm en ded metho d is con n ecting lines
(3/8“ refrigerant hoses designed for vacuum
service)asshowninFigure4-2.
c. Make sure vacuum pump valve is open.
d. Start the vacuum pump. Slowly open valves
halfway and then open vacuum gauge valve.
e. Evacuate unit until vacuum gauge indicates 2000
microns (Hg vacuum). Close gauge valve, vacuum
pump valve, and stop vacuum pump.
f. Break t he vacuum with nitrogen. Raise system
pressure to approximately 2 psig (0.14 bar).
g. Purge the nitrogen from the system.
h. Repeat steps d. thru f. one time.
i. Start vacuum pump and open all valves.
Dehydrate system to 500 microns (Hg vacuum).
j. Close off pump valve, and stop pump. Wait 5
minutes to see if vacuum holds.
k. Ch arge system. Refer to paragraph 4.8.
4.7 PROCEDURE FOR EVACUATION AND DEHYDRATING
SYSTEM (ONE TIME EVACUATION)
a. Remove all refrigerant using a refrigerant recovery
(reclaimer) system (Refer to paragraph 4.4)
b. The recomm en ded metho d is con n ecting lines
(3/8“ refrigerant hoses designed for vacuum
service)asshowninFigure4-2.
c. Make sure vacuum pump valve is open.
d. Start the vacuum pump. Slowly open valves
halfway and then open vacuum gauge valve.
e. Evacuate unit until vacuum gauge indicates 500
microns (Hg vacuum). Close gauge valve, vacuum
pump valve, and stop vacuum pump.
f. Close off pump valve, and stop pump. Wait 5
minutes to see if vacuum holds.
g. Charge system. Refer to paragraph 4.8.
4.8 ADDING REFRIGERANT TO A SYSTEM
4.8.1 Checking Refrigerant Charge
The following conditions must be met to accurately
check the refrigerant ch arge.
a. Bus engine operating at high idle.
b. Air conditioning system operating in high cool 10
to 15 minutes.
c. Com p ressor discharge (head) pressure a minimum
of 150 psig with R134a. It may be necessary to
block condenser air flow to raise discharge
pressure.
d. On the large split systems that are equipped with a
liquid line receiver, the system is prop erly charged
when the refrigerant level is at 1/2 to 3/4 of the
receiver sight glass. If it is n o t at the proper level,
add or remove refrigerant to bring it ro the proper
level.
e. On the smaller split systems refer to Table 4-5 to
determine if correct charge has been obtained.
4.8.2 Adding Full Charge
a. Install manifold gauge set at the suction and
discharge service valves. See Figure 4-2.
b. Evacuate and dehydrate system. (Refer to
paragraph 4.6 ).
c. Place R134a refrigerant cylinder o n scales.
d. Calculate the approximate refrigerant charge using
either Table 4-1, Table 4-2 or Table 4-3. Open the
liquid valve on refrigerant cylinder. Open the
discharge line service port coupler and allow
refrigerant to flow into t h e unit u ntil the correct
weight of refrigerant h as been added as indicated
by scales.
e. Backseat discharge service cou p ler (to close off
gauge port). Close liquid valve on cylinder.
f. Start unit in cooling mode. Run approximately 10
minutes and check the refrigerant ch arge. (Refer to
paragraph 4.8.1)
4.8.3 Adding Partial Charge
a. Examine the unit refrigerant system for any
evidence of leaks. Repair as necessary. (Refer to
paragraph 4.5.)
b. Maintain the conditions outlined in paragraph
4.8.2.
c. Con n ect charging line between suction service
port and cylinder of refrigerant R-134a. Open
VAPOR valve.
d. Slowly add charge as required. Refer to Table 4-5.
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