MCC 50-2104 - Procedure for Evacuation and Dehydrating System (One Time Evacuation)

4-8
© 2015 Mobile Climate Control
T-367 Rev. 05/2015
b. Essential tools to properly evacuate and dehydrate
any system include a good two stage vacuum
pump with a minimum of 6 cfm (10.2 m
3
/hr) vol
ume displacement.
c. Keep the ambient temperature above 60°F
(15.6°C) to speed evaporation of mo isture. If am
bient temperature is lower than 60°F(15.6°C), ice
may form before moisture removal is complete.
4.6.3 Procedure for Evacuation and Dehydrating Sys-
tem (One Time Evacuation)
a. Remove refrigerant using a refrigerant recovery
system. Refer to paragraph 4.4.3.
b. The recomm ended method is connecting lin es (re
frigerant hoses designed for vacuum service) as
showninFigure4-5.
c. Energize the Liquid Line Solenoid Valve (LSV)
(Item 12 in Figure 4-5) using an external power
source (24 VDC).
d. Start vacuum pump. Slowly open valves halfway
and then open vacuum gauge valve.
e. Evacuate unit until vacuum gauge indicates 500
microns Hg vacuum.
f. Close off pump valve and stop pump. Wait five
minutes to see if vacuum holds below 1000 mi
crons.
g. Close vacuum gauge valve to prevent damage to
vacuum gauge. Vacuum gauges should never be
exposed to positive pressure to avoid damage or
affect the vacuum gauge calibration.
h. Charge system. Refer to paragraph 4.7.3.
4.6.4 Procedure for Evacuation and Dehydrating Sys-
tem (Triple Evacuation)
a. Remove refrigerant using a refrigerant recovery
system. Refer to paragraph 4.4.3.
b. The recomm ended method is connecting lin es (re
frigerant hoses designed for vacuum service) as
showninFigure4-5.
c. Energize the Liquid Line Solenoid Valve (LSV)
(Item 12 in Figure 4-5) using an external power
source (24 VDC).
d. Start 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 the vacuum with n itrogen. Raise system
pressure to approximately 2 psig.
g. Purge the nitrogen from the system.
h. Repeat steps d. thru g. one time.
i. Start vacuum pump and open all valves. Dehy
drate unit to 500 microns Hg vacuum.
j. Close off pump valve , and stop pump. Wait five
minutes to see if vacuum holds.
k. Close vacuum gauge valve to prevent damage to
vacuum gauge. Vacuum gauges should never be
exposed to positive pressure to avoid damage or
affect the vacuum gauge calibration.
l. Charge system. Refer to paragraph 4.7.3.
4.7 CHECKING AND ADDING REFRIGERANT TO SYSTEM
4.7.1 Checking Refrigerant Charge By Pressures
For the purpose of checkin g refrigerant pressures to
determine if t h e approximate charge level is co rrect,
the following conditions and method can be used:
a. Install Manifold G auge set as described in Para
graph 4.4.1
b. Coach engine operating at high idle.
c. Unit operating fully loaded in cool mode for 15
minutes.
d. Compressor discharge (head) pressure to 150
PSIG (R-134a) . (It may be necessary to heat the
coach to provide sufficient heat load).
e. Under the above conditions, the “Rule ofThumb”
method can be used as a reference for proper
charge level. See Figure 4-6.
“Rule of Thumb”
Air Conditioning System Pressures
For Discharge Pressure
Condenser Inlet Temperature __________ _ F
Plus (Constant) 40 _ F
Equals __________ _ F
P/T Chart Temperature __________ PSIG
For Suction Pressure
Evap. Return Air Temperature __________ _ F
Minus (Constant) 30 _ F
Equals __________ _ F
P/T Chart Temperature __________ PSIG
Figure 4-6 Rule of Thumb