Lennox SL18XP1 Installation Instruction page 17

Deep Vacuum Gauge Response and
System Conditions
FIGURE 16
Triple Evacuation Method
The triple evacuation method should only be used when
system does not contain any water in liquid form and vacu­
um pump is only capable of pulling down to 28 inches of
mercury (711mm Hg). Refer to figure 17 and proceed as
follows:
Triple Evacuation Sequence
BREAK VACUUM WITH DRY NITROGEN
BREAK VACUUM WITH DRY NITROGEN
CHECK FOR TIGHT, DRY SYSTEM (IF IT HOLDS DEEP VACUUM)
CHARGE SYSTEM
FIGURE 17
1. Pull system down to 28 inches of mercury (711mm Hg)
and allow pump to continue operating for an additional
15 minutes.
2. Close manifold valves or valve at vacuum pump and
shut off vacuum pump.
3. Connect a nitrogen cylinder and regulator to system
and fill with nitrogen until system pressure is 2 psig.
EVACUATE
WAIT
EVACUATE
WAIT
EVACUATE
4. Close nitrogen valve and allow system to stand for one
hour. During this time, dry nitrogen will diffuse
throughout the system, absorbing moisture.
5. Repeat this procedure as indicated in figure 17.
6. After the final evacuate sequence, confirm there are
no leaks in the system. If a leak is found, repeat the en­
tire process after repair is made.
7. Reconnect the manifold gauge to the vacuum pump,
turn the pump on, and continue to evacuate the line set
and indoor unit until the absolute pressure does not
rise above 500 microns (29.9 inches of mercury) within
a 20*minute period after shutting off the vacuum
pump and closing the manifold gauge valves.
8. Disconnect the manifold hose from the vacuum pump
and connect it to an inverted cylinder of HFC*410A
positioned to deliver liquid refrigerant. Open the mani­
fold gauge valve 1 to 2 psig in order to release the va­
cuum in the line set and indoor unit.
9. Perform the following:
S
Close manifold gauge valves.
S
Shut off HFC*410A cylinder.
S
Slowly open the service valves.
S
Refer to the charging sticker on the unit to com­
plete the outdoor unit installation.
Charging
The SL18XP1 unit is factory-charged with enough
HFC-410A refrigerant to accommodate a 15-foot length of
refrigerant piping. Charge should be checked and adjusted
using the tables provided on the charging procedure stick­
er on the unit access panel. Detailed information is given in
the SL18XP1 Installation and Service Procedures manual,
which is available on DaveNet.
Heat Pump Control -- Defrost Operation
A full description of the heat pump control can be found in
the detailed installation and service procedure manual
available on DaveNet. The defrost termination pins (E47)
must be set on the heat pump control prior to starting the
system to ensure proper defrost operation.
The heat pump control (A175) measures differential tem­
peratures to detect when the system is performing poorly
because of frost build-up on the outdoor coil. The heat
pump control self-calibrates when the defrost system
starts and after each system defrost cycle. The heat pump
control monitors ambient temperature, outdoor coil tem­
perature, and total run-time to determine when a defrost
cycle is required. The coil temperature sensor is designed
with a spring clip to allow mounting to the outside coil tub­
ing. The location of the coil sensor is important for proper
defrost operation.
NOTE - The heat pump control accurately measures the
performance of the system as frost accumulates on the
outdoor coil. This typically will translate into longer running
time between defrost cycles as more frost accumulates on
the outdoor coil before the heat pump control initiates de­
frost cycles.
Page 17
SL18XP1 SERIES