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LV Heat Pump Series
Low Voltage
For heat pumps with PSC or constant torque fan motors,
all thermostat wiring is connected to a terminal block
located in the unit electrical box. For heat pumps with a
constant airflow fan motor thermostat wiring is
connected to a removal terminal strip located on the
ECM (Electronically Commutated Motor) control board
located in the electrical box. Refer to the unit wiring
diagram for connection details.
CAUTION: Never route control wiring
through the same conduit as power supply
wiring.
Unless provided with DDC controls, the unit heat pump
can be controlled by most commonly available single-
stage heat pump thermostats. Note that the reversing
valve on the unit is energized when the unit is in the
cooling mode. Thermostats should be located on an
interior wall away from supply ducts. Avoid locations
subject to direct sunlight, drafts, external walls.
Thermostat wiring should be 18AWG (American Wire
Gage). refer to the installation instructions of the
thermostats for further details.
NOTICE: Exceptionally long runs of
thermostat wire should be avoided to
prevent voltage drops in the control circuit.
See Table #1 and #2 for recommended
length
Unit heat pumps are supplied with a 50VA control
transformer as a standard. Models with DDC, hot gas
reheat or an economizer are supplied with a 75 VA
transformer. The 75 VA and 100 VA transformers are
available as optional components for most models (size
018 and larger for 100 VA). The VA capacity of the
transformer should be considered when connecting low
voltage accessories to the heat pump such as
thermostats or solenoid valves. Table # 3 shows the VA
draw of factory mounted components in the low voltage
heat pump. The total VA draw of the heat pump internal
components plus attached accessories must be lower
than the VA capacity of the unit control transformer.
NOTICE: Exceeding the transformer
capacity can result in low control voltage,
erratic unit operation or damage to the heat
pump.
LV Heat Pump Series
Thermostat to HVAC Equipment
The thermostat may not function properly if the total
resistance of any of the thermostat to HVAC equipment
wires exceeds 2.5 ohms. To ensure that wire length does
not cause excess resistance, refer to Table # 1and
ensure that the wires from the thermostat to the HVAC
equipment are not too long.
Table 1: Copper
wire size
2
22 AWG (0.33mm
)
2
20 AWG (0.50mm
)
2
18 AWG (0.75mm
)
Remote Sensor to Programmable Thermostat
Because remote temperature sensors measure
resistance, very long cable runs can cause slight errors
in the measurement. For the highest temperature
reading accuracy, avoid exceeding the maximum
recommended wire lengths show in Table # 2.
Table 2: Copper
wire size
2
22 AWG (0.33mm
)
2
20 AWG (0.50mm
)
2
18 AWG (0.75mm
)
Table 3: Low Voltage VA Draw
STANDARD
HOT GAS REHEAT
CONSTRUCTION
OR ECONOMIZER
Component
VA
Component
Blower Relay
6-7
Total from
(PSC motors
'Standard'
only)
Reversing
8-9
Additional
Valve
Control
Solenoid
Relays
Compressor
6-8
Hot Gas
Contactor
Reheat
Solenoid
UPM Board
2
Total VA draw
22-26
Total VA
draw
Installation | 11
Maximum recommended
wire length
150 ft (46m)
240 FT (73m)
385 FT (117m)
Maximum recommended
remote sensor wire length
1000 ft (300m)
1500 FT (450m)
2500 FT (750m)
OPTIONAL
COMPONENTS
VA
Component
VA
22-26
Monitor Relay
6-7
(VA draw per
relay)
12-14
Internal 2
7
Way
Motorized
Valve
8-9
LED
1
Annunciator
42-49
8 733 905 683 (2016/09)
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