292424-XIM-A-0307
Unitary Products Group
13
third compressor stage is called for by the thermostat. As
such, it’s a “Pump Out On Start Up” design. A normally closed
solenoid valve (POS1) is placed in the liquid line.
When cooling is not being called for by the thermostat, the
pump out solenoid (POS) is not energized, so it’s in the
closed position. When the Simplicity™ control receives a call
for cooling, it energizes a compressor. With the POS being
closed, it causes the pressure on the low side of the system
to begin falling.
When the low pressure switch (LPS) opens, the control board
energizes its on-board pump out relay, providing a 24vac out-
put to an external relay used to energized the pump out sole-
noid. The refrigeration circuit being controlled is not in normal
operating mode.
If the low pressure switch is already open on a call for cool-
ing, the pump out relay is energized immediately. If the LPS
does not open after 5 minutes, the pump out relay is ener-
gized.
CONTINUOUS BLOWER
By setting the room thermostat to “ON,” the supply air blower
will operate continuously.
INTERMITTENT BLOWER
With the room thermostat fan switch set to “AUTO” and the
system switch set to either the “AUTO” or “HEAT” settings,
the blower is energized whenever a cooling or heating opera-
tion is requested. The blower is energized after any specified
delay associated with the operation.
When energized, the indoor blower has a minimum run time
of 30 seconds. Additionally, the indoor blower has a delay of
10 seconds between operations.
COOLING SEQUENCE OF OPERATION
When the thermostat calls for the first stage of cooling, the
low-voltage control circuit from the “R” to “Y1” and “G” is com
-
pleted. The Simplicity™ control board activates the first stage
of cooling by energizing compressor one and both condenser
fans. After completing the specified fan on delay for cooling,
the Simplicity™ control board w ill energize the indoor blower
motor.
When the thermostat calls for the second stage of cooling,
the low-voltage control circuit from “R” to “Y2” is completed.
The control board will energize compressor two.
If there is an initial call for both stages of cooling, the Simplic-
ity™ control board will delay energizing compressor two by
30 seconds in order to avoid an excessive power rush.
Once the thermostat has been satisfied, the Simplicity™ con -
trol board will de-energize Y1 and Y2. If the compressors
have satisfied their minimum run times, the compressors and
condenser fans are de-energized. Otherwise, the unit oper-
ates each cooling stage until the ASCD has elapsed. Upon
the completion of first stage cooling, the blower is stopped
following the completion of the fan off delay cycle.
FLASH CODES
Various flash codes are utilized by the unit control board
(UCB) to aid in troubleshooting. Flash codes are distin-
guished by the short on and off cycle used (approximately
200ms on and 200ms off). To show normal operation, the
control board flashes a 1 second on, 1 second off "heartbeat"
during normal operation. This is to verify that the UCB is func-
tioning correctly. Do not confuse this with an error flash code.
To prevent confusion, a 1-flash, flash code is not used.
Alarm condition codes are flashed on the UCB lower left Red
LED, See Figure 6. While the alarm code is being flashed, it
will also be shown by the other LEDs: lit continuously while
the alarm is being flashed. The total of the continuously lit
LEDs equates to the number of flashes, and is shown in the
table. Pressing and releasing the LAST ERROR button on
the UCB can check the alarm history. The UCB will cycle
through the last five (5) alarms, most recent to oldest, sepa-
rating each alarm flash code by approximately 2 seconds. In
all cases, a flashing Green LED will be used to indicate non-
alarm condition.
In some cases, it may be necessary to "zero" the ASCD for
the compressors in order to perform troubleshooting. To reset
all ASCDs for one cycle, press and release the UCB TEST/
RESET button once.
Flash codes that do and do not represent alarms are listed in
Table 9 .
