035-14511-000 REV B (1299)
Unitary Products Group
13
®
sor in the second stage mode. Additionally, the control
outputs a 24v signal (at Y2 OUT) to control the indoor blower
at the correct CFM.
If there is a call for second stage cooling (Y2) prior to the unit
operating the first stage (i.e. if call occurs during the five
minute anti-short cycle period), then the control will switch the
control circuit and will energize the contactor starting the out-
door fan and the compressor in the second stage mode.
Additionally, the control outputs a 24v signal (at Y2 OUT) to
control the indoor blower at the correct CFM.
When the second stage of the room thermostat is satisfied
only, the unit will continue to operate in the second stage
mode.
When the first stage of the room thermostat is satisfied, the
control will de-energize the contactor stopping the outdoor
fan and the compressor.
If the room thermostat calls for second stage cooling (Y2) on
two consecutive cooling cycles, the next call for cooling for
either first (Y1) or second (Y2) stage will energize the unit in
the second stage mode. The above mode will be reset to per-
mit start up on first stage with only a Y1 call when the second
stage operational cycle runs less than 15 minutes. This mode
can also be reset when servicing the equipment by removing
24 V to the control.
NOTE: The control with not operate on Y2 without a Y1 signal.
SYSTEM CONTROL BOARD FUNCTIONS
Refer to Figure 11 for view of Control Board.
Five Minute Anti-Short Cycle Timer
The control has a five minute time delay to prevent the sys-
tem from short cycling after a thermostat off cycle or power
interrupt. This five-minute delay is initiated following the com-
pletion of a first stage cooling call (Y1) or the 24v power up of
the control. During this mode the control will not respond to
any thermostat inputs and the LED will flash a code 1 at the
control board.
For servicing or during installation of the condensing unit, the
time delay may be by-passed by momentarily jumping the
two test pins when there is a call for cooling (Y1 or Y2).
Pressure Switch Operation
The condensing unit is provided with high and low pressure
switches installed and wired into the control to provide addi-
tional protection for the system if any abnormal operating
conditions occur. The high pressure switch is threaded on a
Schrader fitting located in the liquid line of the outdoor unit
and a low pressure switch is brazed in the suction line of the
outdoor unit. These two controls are wired in series to the unit
control.
If the pressure switches detect a fault condition, they will
open (high pressure opens with pressures greater than 400
psi and low pressure opens with pressures less than 25 psi)
and the control will immediately shut down the unit. The con-
trol will go into a five-minute anti-short cycle mode inhibiting
any thermostat inputs. Following the anti-short cycle mode,
the control will permit the unit to start normally with the next
call for cooling as long as the pressure switches have reset
(high pressure resets at 300 ± 15 psi, low pressure resets at
65 ± 7 psi).
If the control detects a second pressure switch fault within
one hour of compressor run time, the unit will again shut
down and the unit control will lock out the unit until the fault
condition is reset. During this period, a code “2” will be
flashed at the control and provide a 24v signal on the X/L line
to flash at the room thermostat.
Indoor Blower Operation
The indoor blower operation is controlled directly by the Y1 or
G thermostat signal for the first stage of cooling and by
Y2OUT from the control for the second stage of cooling. The
reason the unit control controls the second stage blower is
that the control will override the thermostat and continue sec-
ond stage once the second stage of the thermostat is satis-
fied and there is still a first stage demand. Additionally, during
the five second switching from first to second stage, the
blower ramp up is delayed.
.
FIGURE 11 : COMFORT ENHANCER
™
CONTROL
BOARD
T E S T
R
L
Y 2
Y 1
M
C
Y 2 O U T
P S
S T A T U S
E X T E R N A L R L Y
T S C O N T R O L
TEST
PINS
LED
