035-20401-001 Rev. A (0904)
16
Unitary Products Group
The control only reads the jumper inputs when the Y1, Y2, and W ther-
mostat inputs are de-energized. If a jumper position is changed while
any of these inputs are energized, the control will not act upon the
jumper changes until all three of these thermostat calls are de-ener-
gized or power (24 VAC) to the control is cycled.
IMPORTANT: Changes to the jumper inputs do not take affect until
Y1, Y2, and W thermostat signals are de-energized.
LOW TEMPERATURE CUTOUT (LTCO) AND
BALANCE POINT (BP)
The control includes a low temperature cutout (LTCO) feature that pre-
vents compressor operation below a specified temperature during heat
pump heating operation only. The LTCO setting does not apply to com-
pressor operation during cooling or defrost operation.
The control also includes a balance point feature that prevents the
operation of auxiliary heat above a specified temperature.
Setting
The LTCO and BP jumpers on the control are shown in Figures 11 & 14.
Both jumpers are placed on the same connector. The control will con-
sider the lowest jumper pin setting to be the LTCO and the highest
jumper pin setting to be the BP. The use of the same connector forces
the BP and the LTCO to always be separated by at least 10 degrees.
The temperatures shown on the side of the connector labeled LTCO are
the LTCO temperature options. The values shown are in degrees F. The
control allows the LTCO to be set to any of the following temperatures: -
10, 0, 10, 15, 20, 25, 30, 35 degrees F or ON. Placing the jumper in the
ON position will allow the control to operate the compressor at any tem-
perature during heating operation.
The factory places the LTCO jumper in the ON position. The jumper
must be changed in the field to implement the LTCO feature. If the
jumper is removed, the control will behave as if the jumper is in the ON
position.
The temperatures shown on the side of the connector labeled BP are
the BP temperature options. The values are shown in degrees F. The
control allows the balance point to be set to any of the following temper-
atures: 0, 10, 15, 20, 25, 30, 35, 40, or 45 degrees F.
The factory places the BP jumper in the 35 F position. The jumper may
be changed in the field as desired. If the jumper is removed, the control
will behave as if the jumper is in the 35 position.
If only one jumper is in place, the control will set the balance point
based on the jumper position and will set the LTCO to ON. If only one
jumper is in place and it is below the valid BP settings (in the –10 or ON
position), the control will set the BP to the default value for no jumper in
place (35F) and set the LTCO based on the jumper position (-10 or
ON).
Low Temperature Cutout (LTCO) Operation
The control will not operate the compressor in heating mode when the
outdoor ambient temperature is below the selected LTCO. The LTCO
applies only to air handler mode operation. In fossil fuel mode the bal-
ance point (BP) restricts the operation of the compressor so the LTCO
setting has no effect.
Balance Point (BP) Operation
If the measured outdoor ambient temperature is greater than the bal-
ance point setting, the control will not energize the auxiliary heat out-
puts. However, the control shall ignore the balance point setting and
energize auxiliary heat under some conditions as described in the auxil-
iary heat sections of this document.
FOSSIL FUEL JUMPER (FFUEL)
Setting
The control includes a FFUEL jumper to specify whether the control is
installed with a fossil fuel furnace or an air handler (electric heat). This
jumper is shown in Figures 11 & 14. The factory places the FFUEL
jumper in the OFF position which is the correct position for an air han-
dler installation. The jumper must be changed to the ON position in the
field if the heat pump is installed with a fossil fuel furnace. If the jumper
is removed, the control will behave as if the jumper is in the OFF posi-
tion.
IMPORTANT: If the heat pump is being installed with a fossil fuel
furnace, the FFUEL jumper must be placed in the ON position dur-
ing installation for proper system operation.
Operation
The control operates the auxiliary heat outputs, W1 OUT and W2 OUT,
based on the position of the FFUEL jumper. If the FFUEL jumper is in
the ON position, the control will function in fossil fuel mode. If the
jumper is in the OFF position, the control will function in air handler
mode. The FFUEL jumper has no effect on cooling operation.
AUXILIARY HEAT - AIR HANDLER MODE
The heat pump control energizes the auxiliary electric heat in air han-
dler mode using the W1 OUT and W2 OUT signals. The control
receives the room thermostat call for auxiliary heat at the W input termi-
nal.
Standard Operation
If the outdoor ambient temperature is less than ten degrees F below the
balance point setting and a W input is received with a Y1 or Y1 + Y2
input, the control will energize the M compressor contactor output
based on the Y1 input and will energize the W1 OUT immediately when
the W input is received. When the W input is received, the control will
start a fifteen-minute timer. If the call for Y1 + W or Y1 + Y2 + W is still
present after the fifteen-minute timer expires, the control will then ener-
gize W2 OUT along with W1 OUT. If the W input is removed but the Y1
or Y1 + Y2 signal remains, the control will de-energize W1 OUT and W2
OUT (if energized) and reset and restart the timer. If the W input is
received again without a loss of the Y1 or Y1 + Y2, the same functional-
ity will be repeated.
If the outdoor ambient temperature is ten degrees F or more below the
balance point setting and a W input is received with a Y1 or Y1 + Y2
input, the control will energize W1 OUT and W2 OUT immediately.
If the outdoor ambient temperature is below the low temperature cutout
(LTCO) setting, the control will de-energize the compressor and ener-
gize W1 Out immediately when a Y1 input is received and W2 out
immediately when the Y2 input is received. If the outdoor ambient tem-
perature rises above the LTCO setting before the thermostat is satis-
fied, the control will continue to keep the compressor outputs de-
energized until the thermostat is satisfied. In other words, the control
will use auxiliary heat to satisfy the thermostat demand and not turn the
compressor back on even if the outdoor ambient temperature rises
above the LTCO setting during a call for heating.
FIGURE 14:
Jumper Inputs
