BALANCE POINT
This feature can be used in 2 different options: furnace interface or
electric heat staging. Refer to the Furnace Interface section for its
application. If heat pump is installed with a fan coil with
multistages of electric heat, this option can be used to stage the
banks of heat by outdoor ambient. This eliminates the need for
accessory outdoor thermostats.
When using this option to stage electric heat, the first stage is
energized by a W2 demand, and second stage is energized by a W3
demand. Select the W3 desired temperature by rotating BAL-
ANCE POINT pot. (See Fig. 9 or 11.) Temperatures that may be
selected are 10°, 15°, 20°, 25°, 30°, 35°, 40°, and 45°F. The pot is
factory set at 45°F.
LOW-SPEED HEATING WITH AUXILIARY HEAT
If system is operating in low-speed heating and there is a demand
for auxiliary heat (W2), the system changes to high-speed opera-
tion. W2 is energized unless low-voltage control wiring is config-
ured as shown in Fig. 12.
AUXILIARY HEAT (W2) LOCKOUT
In some areas, it is necessary to disable auxiliary heat, except for
defrost, until outdoor ambient is less than the structure’s balance
point. This is accomplished by using the low-voltage wiring shown
in Fig. 12. Wire the 24-vac W2 signal from indoor thermostat to
W3 of control, and W2 of control to W2 of indoor unit. When
outdoor ambient is less than setting of BALANCE POINT pot, the
24-vac signal energizes auxiliary heat (W2) of indoor unit.
EMERGENCY HEAT
If the 2-speed control receives a call for auxiliary heat (W2)
without a heat pump heating (Y1) call, second auxiliary stage (W3)
is energized. This ensures all available heat is energized if indoor
thermostat is switched to emergency heat.
COMPRESSOR PTC OVERLOAD PROTECTION
The control senses the resistance of the compressor internal
positive temperature coefficient (PTC) overloads. If PTC resis-
tance is out of range, control shuts unit off until resistance range is
acceptable. See Table 10 for compressor PTC ranges.
When control turns outdoor unit off due to out of range PTCs, unit
remains off for 15 minutes with outdoor fan running. After 15
minutes, control checks resistance every 5 minutes until it reaches
reset range. During this time, a malfunction signal appears at
control board. If a PTC trip occurs 3 times, the control locks out
outdoor unit operation and provides a malfunction signal at
control.
PRESSURE SWITCH PROTECTION
The outdoor unit is equipped with high- and low-pressure
switches, wired in series. If the control senses the opening of a
pressure switch, it provides a 5-minute time delay in outdoor unit
operation with outdoor fan running. A malfunction signal appears
on control when pressure switch opens. If pressure switch remains
open for 1 hr or longer, a malfunction signal is provided at L
terminal on indoor thermostat.
MAJOR COMPONENTS
2-Speed Control
The 2-speed control board controls the following functions:
•
High- and low-compressor contactor operation
•
Outdoor fan motor operation
•
Crankcase heater operation
•
Compressor protection
•
Pressure switch monitoring
•
Second-stage latching
•
Time delays
•
Time/temperature defrost
•
Defrost interval selection
•
Zoning
•
Furnace interface
•
Electric heat staging
Refer to other headings in the System Functions and Sequence of
Operation section for individual function information.
Header Pin Housing
The header pin housing is the plastic assembly which holds the
stripped lead ends for field connections. The 2-speed control
receives 24-vac low-voltage control system inputs through the
housing/pins. The housing also contains jumpers which the control
uses for system configuration, such as heat pump versus air
conditioner. Refer to Fig. 13 for header pin housing configuration.
2-Speed Compressor
The 2-speed compressor contains motor windings that provide
low-speed, 4 pole (1750 RPM) and high-speed, 2-pole (3500
RPM) operation. Refer to Table 11 for appropriate winding
resistances. Refer to unit wiring label for winding configurations.
Fig. 12—Low-Voltage Control Wiring
A93572
W2
W3
W3
W2
W2
TWO SPEED
THERMOSTAT
TWO SPEED
HEAT PUMP
FAN
COIL
CONTROL
LOGIC
Table 10—Compressor PTC Ranges
COMPRESSOR INTERNAL PTC RESISTANCE
Safe range (77°F)
1.5k to 7.8k ohms
To trip
26k to 34k ohms
To reset
8.4k to 10k ohms
Fig. 13—Header Pin Housing Configuration
A93576
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
JUMPER FOR
HEAT PUMP ONLY
C - TRANSFORMER COMMON
R - TRANSFORMER LINE
W2 - FIRST STAGE AUXILIARY HEAT
O - REVERSING VALVE
Y2 - SECOND STAGE COOLING/HEAT PUMP
L - MALFUNCTION LIGHT
Y1 - FIRST STAGE COOLING/HEAT PUMP
W3 - SECOND STAGE AUXILIARY HEAT
4 - TON
5 - TON
IF NO JUMPER IS
INSTALLED, DEFAULT
IS 3 - TON
18
