Page 21
XP21 SERIES
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:
Close manifold gauge valves.
Shut off HFC
*
410A cylinder.
Slowly open the service valves.
Refer to the charging sticker on the unit to com
plete the outdoor unit installation.
Charging
The XP21 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 sticker on the
unit access panel. Detailed information is given in the
XP21 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.
Homeowner Information
CAUTION
Before attempting to perform any service or mainte
nance, turn the electrical power to unit OFF at discon
nect switch.
In order to ensure peak performance, your system must be
properly maintained. Clogged filters and blocked airflow
prevent your unit from operating at its most efficient level.
The system should be inspected and serviced before each
cooling and heating season by a licensed professional
HVAC service technician (or equivalent).
Heat Pump Operation
Your new Lennox heat pump has several characteristics
that you should be aware of:
Heat pumps satisfy heating demand by delivering large
amounts of
warm
air into the living space. This is quite
different from gas‐ or oil‐fired furnaces or an electric fur
nace which deliver lower volumes of considerably
hotter
air to heat the space.
Do not be alarmed if you notice frost on the outdoor coil
in the winter months. Frost develops on the outdoor coil
during the heating cycle when temperatures are below
45
°
F (7
°
C). An electronic control activates a defrost
cycle lasting 5 to 15 minutes at preset intervals to clear
the outdoor coil of the frost.
During the defrost cycle, you may notice steam rising
from the outdoor unit. This is a normal occurrence. The
thermostat may engage auxiliary heat during the defrost
cycle to satisfy a heating demand; however, the unit will
return to normal operation at the conclusion of the de
frost cycle.
