035-20401-001 Rev. A (0904)
Unitary Products Group
13
COOLING OPERATION
First-Stage Cooling Operation
During first-stage cooling operation, the control will receive thermostat
signals at the Y1 and O input terminals. The control will energize the M
compressor output terminal. This signal energizes the coil of the com-
pressor contactor causing the compressor to run. The control also
closes the outdoor fan relay delivering power to the ODF terminal caus-
ing the outdoor fan to operate. The control energizes the RV terminal
with 24VAC to switch the reversing valve.
Second Stage Cooling Operation
During second-stage cooling operation, the control will receive thermo-
stat signals from Y1, Y2 and O inputs. The control will energize both the
M and M2 compressor output terminals. The M signal energizes the
compressor contactor causing the compressor to run. The M2 signal
energizes the isolation relay coil which closes the relay’s normally open
contacts. This closure energizes the 24V compressor solenoid causing
the compressor to operate in second stage. During two-stage cooling
operation the control also closes the ODF relay causing the outdoor fan
to operate. The control energizes the RV terminal with 24VAC to switch
the reversing valve. Additionally, the Y2 OUT terminal is energized with
24VAC. This signal can be used to signal the indoor unit to deliver high
air flow.
Two-Stage Cooling Anticipation Mode
The second-stage anticipation mode applies only to cooling operation. It
does not apply to heating operation.
The purpose of this mode is to allow the unit to bypass first stage oper-
ation under very hot conditions when the unit will most likely require
second stage operation anyway.
The factory setting for second-stage cooling anticipation mode is OFF.
If the control receives two consecutive calls for second-stage cooling
(Y1+Y2+O), it shall force second stage compressor operation with the
next call for first stage cooling (Y1+O). The control shall continue to
force second stage cooling operation with thermostat calls for first stage
cooling until one of the following conditions occurs.
•
A thermostat call for first stage cooling (Y1+O) that has duration
of less than 10 minutes.
•
Recycling 24VAC to the control
•
Shorting the TEST input pins.
If the Y2 LOCK jumper is in the OFF position, the control will not imple-
ment second-stage anticipation mode. This results in second-stage
operation only when the room thermostat calls for second-stage cooling
(Y1 + Y2 + 0).
If the jumper is removed, the control will behave as if the jumper is in
the OFF position.
HEATING OPERATION
First-Stage Heating Operation
During first-stage heating operation, the control will receive a thermo-
stat signal at the Y1 input terminal. The control will energize the M com-
pressor output terminal. This signal energizes the coil of the
compressor contactor causing the compressor to run. The control also
closes the outdoor fan relay delivering power to the ODF terminal caus-
ing the outdoor fan to operate. The reversing valve is not energized in
heating mode.
Second-Stage Heating Operation
During second-stage heating operation, the control will receive a ther-
mostat signal at the Y1 and Y2 input terminals. The control will energize
the M and M2 compressor output terminals. The M signal energizes the
coil of the compressor contactor causing the compressor to run. The
M2 signal energizes the isolation relay coil which closes the relay’s nor-
mally open contacts. This closure energizes the 24V compressor sole-
noid causing the compressor to operate in second-stage. The control
also closes the ODF relay causing the outdoor fan to operate. The Y2
OUT terminal may or may not be energized depending on the HP mode
of operation (conventional vs. hot heat pump).
Conventional Heat Pump Mode
The factory setting of the HOT HEAT PUMP jumper on the control is the
OFF position. In this configuration the heat pump operates in conven-
tional heat pump mode. If the jumper is not in place, the control will act
as if the jumper is in the OFF position.
If the HOT HEAT PUMP jumper is in the OFF position, the control will
energize the Y2 OUT terminal whenever the compressor is running in
second-stage.
The location of the hot heat pump jumper is shown in Figures 11 & 14.
FIGURE 12:
Defrost Operation Curves
REGION C
TERMINATE CURVE
INHIBIT CURVE
INITIA
TE CURVE
REGION A
REGION B
REGION D
REGION E
AMBIENT TEMPERATURE
LIQUID LINE (COIL) TEMPERA
TURE
Defrost prevented from starting
No call for defrost
Time Defrost (6 hour) prevented
No call for Defrost
Time Defrost (6 hour) allowed
Call for Defrost
Defrost Terminated
