Evacuating And Dehydrating The System - Lennox HP21 Unit Information

CAUTION−WHEN USING DRY NITROGEN, A PRES-
SURE REDUCING REGULATOR MUST BE USED TO
PREVENT EXCESSIVE PRESSURE IN GAUGE
MANIFOLD, CONNECTING HOSES, AND WITHIN
THE SYSTEM. REGULATOR SETTING MUST NOT
EXCEED 150 PSIG (1034 KPA).
2− Open high pressure valve on gauge manifold and pres-
surize line set and indoor coil to 150 psig.
3− Check lines and connections for leaks.
NOTE−If electronic leak detector is used, add a trace of
refrigerant to the nitrogen for detection by the leak de-
tector.
4− Release nitrogen pressure from the system, correct any
leaks and recheck.
B−Evacuating and Dehydrating the System
1− Attach gauge manifold as shown in figure 16. Connect
vacuum pump (with vacuum gauge) to center port of
gauge manifold. With both manifold service valves
open, start pump and evacuate indoor coil and refriger-
ant lines.
NOTE−A temperature vacuum gauge, mercury vacuum
(U−tube), or thermocouple gauge should be used. The
usual Bourbon tube gauges are not accurate enough in
the vacuum range.
2− Evacuate the system to 29 inches vacuum. During the
early stages of evacuation, it is desirable to stop the
vacuum pump at least once to determine if there is a
rapid loss of vacuum. A rapid loss of vacuum would indi-
cate a leak in the system and a repeat of the leak testing
section would be necessary.
3− After system has been evacuated to 29 inches
(737mm), close gauge manifold valves to center port,
stop vacuum pump and disconnect from gauge man-
ifold. Attach an upright nitrogen drum to center port of
gauge manifold and open drum valve slightly to purge
line at manifold. Break vacuum in system with nitrogen
pressure by opening manifold high pressure valve.
Close manifold high pressure valve to center port.
4− Close nitrogen drum valve and disconnect from gauge
manifold center port. Release nitrogen pressure from
system.
5− Reconnect vacuum pump to gauge manifold center
port. Evacuate system through manifold service valves
until vacuum in system does not rise above 29.7 inches
(754mm) mercury (5mm absolute pressure) within a
20−minute period after stopping vacuum pump.
6− After evacuation is complete, close manifold center
port, and connect refrigerant drum. Pressurize system
slightly with refrigerant to break vacuum.
C−Charging
The system should be charged in the cooling cycle if weath-
er conditions permit. The following procedures are
intended as a general guide and slight variations in temper-
ature and pressure should be expected. Large variations
may indicate a need for further servicing.
If the system is completely void of refrigerant, the recom-
mended and most accurate method of charging is to weigh
the refrigerant into the unit according to the total amount
shown on the unit nameplate and in table 14. Refer to the
Lennox Unit Information Service manual for proper proce-
dure.
If weighing facilities are not available or if unit is just low on
charge, the following procedures apply.
BEFORE CHARGING
(steps 1 through 4)
NOTE − The following procedures require accurate
readings of ambient temperature, liquid temperature
and liquid pressure for proper charging. Use a ther-
mometer with accuracy of +2°F and a pressure gauge
with accuracy of +5PSIG.
1− Connect gauge manifold as shown in figure 16. Con-
nect an upright R−22 drum to center port of gauge
manifold.
2− Record outdoor ambient temperature.
3− If indoor temperature is below 74°F, set room thermo-
stat to 74°F (23°C) in Emergency Heat" or Heat"
position and allow unit to run until heating demand is
satisfied. This will create the necessary load for proper
charging of system in cooling cycle. Change thermo-
stat setting to 68°F (20°C) in Cool" position. Allow unit
to run until system pressures stabilize.
4− Make sure thermometer well is filled with mineral oil
before checking liquid line temperature.
NOTE−When checking or adjusting charge, compres-
sor should always be on high speed and indoor blower
should be on cooling high speed. For cooling mode, set
room thermostat at lowest setting. For heating mode,
place a jumper across speed control thermostat (S6) in
outdoor unit and then reset the room thermostat to OFF
and back to HEAT.
OUTDOOR TEMPERATURE ABOVE 60°F
5− If ambient temperature is above 60°F, system should
be charged using the approach method. Place ther-
mometer in well and read liquid line temperature. The
difference between liquid line temperature and ambi-
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(step 5)