Heat Pump; Installing Heat Pump And Accessories; Equipment Installation; Pressure Switch - Lennox HARMONY III Installation, Setup And User Manual

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2.1.

Installing Heat Pump and Accessories

2.1.1.

Equipment Installation

Follow all equipment installation instructions provided with each unit.
2.1.2. Pressure Switch
The high pressure switch is a normally closed (N.C.) auto-reset high pressure
switch located in the compressor discharge line or on the suction valve service
port. The switch is factory set to open when operating pressures rise and close
when the pressure drops (see following table). The intent of the switch is to protect
the outdoor unit from abnormally high operating pressures during mild weather
heating days. The green pressure LED comes on when the heat pump pressure
switch is closed indicated normal condensing pressures.
Table 13. High Pressure Switch Operation
Refrigerant Open on pressure rise (psig)
HFC-22
HFC-410A
NOTE: If a pressure switch is factory installed in the unit, do not remove the switch
or switch wires.
The switch may also be fastened directly to the vapor valve service port which
becomes the discharge line in heat pump heating mode (see "Figure 17. Tee and
Vapor Line High Pressure Switch").
1. Connect refrigerant gauge set to the outdoor unit vapor line.
2. Establish a compressor heating demand and allow system to begin operating
(see heat pump heating checkout section for details). Note that the green
pressure switch LED comes on.
3. Allow system to operate several minutes so refrigerant pressures can balance.
4. Momentarily block the return air opening and observe the high pressure gauge.
When hot gas line pressure reaches the "open on" pressure and the green
pressure switch LED turns off, an error code will be set in the zone control
system, DIAGs 1 and 4 will turn on, and outdoor unit will stage down and turn
off if the switch does not close within 90 seconds. Afterwards, backup heat will
be used to satisfy the demand.
5. Remove the restriction. When hot gas pressure drops below the "close on"
pressure, the green pressure switch LED will turn on and all DIAGs should
turn off.
Close on pressure fall
(psig)
375 275
550 425
2.1.3. Pressure Switch Wiring
Pull a two-wire thermostat cable from the field-installed pressure switch to the zone
control panel and connect at the pressure switch, and at the zone control panel as
shown in the connection location diagram.
2.1.4. Tee (High Pressure Switch; Heat Pumps only)
A tee (Lennox #87071) is needed to install the pressure switch along with a valve
core (Schrader) for checking pressure in the vapor line during heat pump heating
mode. The switch may also be fastened directly to the vapor valve service port
which becomes the discharge line in heat pump mode.
TO
REVERSING
VALVE
VALVE DEPRESSOR TEE
(LENNOX 87071)
NEW SERVICE
PORT
Figure 17. Tee and Vapor Line High Pressure Switch
IMPORTANT
High pressure switch must be installed on open side of tee first to prevent
refrigerant loss.
2.1.5.

Balance Point Sensor (Outdoor Thermostat)

A balance point sensor as illustrated in the following figure may be implemented in
a dual-fuel (Option 3) system. This thermostat monitors the outdoor temperature,
compares it to the balance point setting, and signals the zone control if the reading
is below the set point. The zone control then instructs the gas furnace to provide all
the heating and prohibits the heat pump from attempting to fill a demand for heat.
See "Figure 32. Option 3 - Typical Lennox Heat Pump and Lennox Variable-Speed
Gas Furnace (Dual Fuel) (Troubleshooting)" on page 48 for connecting sensor
switch to Harmony III.
TERMINAL B
Figure 18. Balance Point Sensor (10Z23)
NOTE: In Harmony III zoning system applications, terminal B and R are wired to
the Harmony III zoning system panel.
18
VAPOR LINE
(TO INDOOR
COIL)
HIGH PRESSURE
SWITCH
TERMINAL
R