035-20401-001 Rev. A (0904)
Unitary Products Group
15
Forced Second Stage Feature Operation
The control will force second stage compressor operation when the liq-
uid line temperature is below the switch point even if the thermostat is
calling only for first stage. The liquid line temperature must be below
the switch point continuously for 30 seconds. If the liquid line tempera-
ture exceeds the switch point before 30 seconds has expired, the con-
trol will reset the timer and restart the timer when the liquid line falls
below the switch point again. The liquid line temperature may be fil-
tered to improve system performance if necessary.
The control shall only implement this behavior during a call for first-
stage heating (Y1).
The control will no longer force two-stage compressor when all of the
following conditions are true continuously for 30 seconds. If any of the
conditions are no longer true before the 30-second timer expires, the
control will reset the timer and restart the timer when all of the condi-
tions are again true. That is, if the liquid line temperature exceeds the
switch point temperature then falls below the switch point temperature
before the 30-second timer expires, the control shall reset the timer
when the control falls below the switchpoint. The control shall restart
the 30-second timer when the liquid line temperature exceeds the
switch point temperature again.
1.
The liquid line temperature exceeds the switch point temperature.
2.
The outdoor ambient temperature exceeds the values correspond-
ing to each switch point setting as shown in Table 9.
3.
The unit is not in defrost mode. If the other exit conditions are met
while the unit is in defrost mode, the control will complete the
defrost cycle and then exit the forced second-stage feature.
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 thermostat calls for emergency heat operation (W signal with-
out a Y signal), the control will de-energize the compressor and ener-
gize 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 11 & 14. 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
•
Y2 LOCK – Determines compressor staging
•
SWITCH POINT – Specifies liquid temperature at which second-
stage compressor operation is forced.
TABLE 9:
Switch Point Exit Temperatures
Switch Point Setting
OD Ambient Exit Temp
35
42
40
47
45
55
FIGURE 13:
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)
