170761-UIM-B-0406
14
Unitary Products Group
When the ten-minute timer expires, the control will measure the liquid
line temperature and determine whether to energize Y2 Out and
increase the indoor airflow or keep Y2 Out de-energized and maintain
reduced indoor airflow. The control compares the measured liquid line
temperature to a pre-programmed indoor airflow curve. It continues to
keep Y2Out de-energized until the liquid line temperature exceeds the
curve for the given outdoor ambient temperature continually for 30 sec-
onds. If the liquid line temperature drops below the curve, the control
will reset the 30-second timer and restart it when the liquid line temper-
ature again exceeds the curve. When the liquid line temperature
exceeds the indoor airflow control curve continually for 30 seconds, the
control will energize Y2Out, i.e. cause high indoor airflow, until the ther-
mostat demand is satisfied and the thermostat signal inputs are
removed. Figure 12 describes the required behavior.
Once the control energizes Y2 Out to create high airflow, it will keep Y2
Out energized until the thermostat is satisfied and the call for heating is
removed. It will do this regardless of a change in outdoor ambient or liq-
uid line temperature. Therefore, if the control energizes Y2 Out because
the outdoor ambient temperature is greater than or equal to 50F or
because the liquid line temperature exceeds the curve for the given out-
door ambient temperature (point within region B), it will keep Y2 Out
energized until the thermostat is satisfied even if the liquid line or out-
door ambient temperature falls below the curve (point within region A).
The control of Y2 Out to generate high indoor airflow as required will
prevent the heat pump system pressures and temperatures from
becoming too great when the compressor is running at full capacity with
low indoor airflow.
As an example, assume that the HOT HP jumper is in the ON position.
When the control receives a call for heating (Y1), it checks the outdoor
ambient temperature. If the outdoor ambient temperature is 52F, the
control will energize Y2 Out immediately causing high indoor airflow
and keep it energized until the Y1 signal is removed. If the outdoor
ambient temperature is 48F, the control will maintain Y2 OUT in a de-
energized state and begin a ten-minute timer. The indoor unit will be
running at low airflow because of the Y1 signal being delivered to the
Y1 input of the indoor unit.
When the ten-minute timer expires, the control will compare the liquid
line temperature to the indoor airflow control curve for the measured
outdoor ambient temperature. If the point is within region A (See Figure
12), the control shall maintain Y2 OUT in the de-energized state until
the liquid line temperature rises so that region B is entered. While in
region A, the indoor unit will continue to run at low airflow. When the liq-
uid line temperature point enters region B, the control will start a 30 sec-
ond timer. When the timer expires, the control will immediately energize
Y2 OUT. If the liquid line temperature drops back into region A before
the timer expires, the control will reset the timer and restart it when the
liquid line temperature again enters region B. When the liquid line tem-
perature is in region B continually for thirty seconds, the Y2 Out signal
will be delivered to the indoor unit and cause high airflow.
During defrost operation, the control will ignore the HOT HP jumper set-
ting and energize the Y2 Out signal to create high indoor airflow. Addi-
tionally, if at any point the conditions require a defrost cycle, the control
will override the reduced indoor airflow feature and function based on
the defrost requirements and conditions.
EMERGENCY HEAT
When the control receives a W signal without a Y signal (emergency
heat), the control will de-energize the compressor and energize the W1
Out and W2 Out terminals immediately. The balance point setting is
ignored during a call for emergency heat. Therefore, W1 Out and W2
Out will be energized regardless of the outdoor ambient temperature.
JUMPER INPUTS
The control uses seven jumpers to determine how the heat pump
should operate. These jumpers are shown in Figures 10 and 13. The
jumpers that affect this heat pump are the following. The effects of
these jumper settings on the operation of the heat pump are described
in other sections of this document.
•
LTCO – Low Temperature Cutout
•
BP – Balance Point
•
Defrost Curve
•
FFUEL – Specifies fossil fuel furnace application
•
HOT HEAT PUMP – Enables indoor airflow control for hot heat
pump application
The two jumpers that do not affect the operation of this heat pump are
Y2 LOCK and SWITCH POINT. Both of these jumpers apply only to
two-stage compressor units.
FIGURE 11: Hot Heat Pump Indoor Airflow Control
IN
DO
O
R
AI
RF
LO
W
C
O
NT
RO
L
CU
RV
E
REGION A
REGION B
AMBIENT TEMPERATURE
LI
Q
U
ID LINE
(
C
OIL) T
E
M
PER
AT
URE
Y2Out Energized (High Indoor Airflow)
Y2Out De-energized (Low Indoor Airflow)
