035-19315-001-A-0603
38
Unitary Products Group
The ASCD is initiated on unit start-up and on any com-
pressor reset or lock-out.
FLASH CODES
The UCB will initiate a flash code associated with
errors within the system. Refer to UNIT CONTROL
BOARD FLASH CODES Table 29.
RESET
Remove the call for cooling, by raising thermostat set-
ting higher than the conditioned space temperature.
This resets any pressure or freezestat flash codes.
HEATING SEQUENCE OF OPERATIONS
WITH OR WITHOUT ELECTRIC HEAT
When the thermostat calls for the first stage of heating,
the low voltage control circuit is completed between “R”
and “W1”. The 24vac signal is passed through the UCB
to the “Y” contact on the Defrost Control (DC) assuring
the reversing valve cannot be energized, except during
defrost. If the ASCD timer is satisfied the UCB will
energize compressor contactor M1.
If the compressor alone cannot satisfy the heating
requirements a second stage call from the thermostat
completes the circuit between “R” and “W2”. This
24vac signal is passed through the UCB to the electric
heat section (if available). The total available kW of
electric heat will be energized on a call for “W2”.
DEFROST MODE
As mentioned earlier, the defrost control (DC) utilizes a
time/temperature defrost scheme. The following two
conditions must be met before the DC will enter a
defrost mode:
1.
The defrost thermostat (SD) must be closed. This
normally open thermostat is mounted on the liquid
line and is set to close at 28 ± 4°F.
2.
Once the defrost thermostat closes, the defrost
control starts a run timer that must be satisfied
before defrost can begin. This is accumulated com-
pressor run time. The selection pin is factory set at
60 minutes, but is field adjustable to 30, 60 or 90
minutes.
When the DC enters the defrost mode, it’s on-board
defrost relay is powered. This energizes the reversing
valve, de-energizes the condenser fan motor and ener-
gizes the unit’s optional electric heater. The DC
remains in defrost mode until either of the following two
conditions is met:
1.
The liquid line thermostat is open. It is set to open
at 55 ± 4°F.
2.
The maximum defrost run time of 10 minutes is
met.
SAFETY CONTROLS
The control circuit includes the following safety con-
trols:
1.
Temperature Limit Switch (TLS) - This control is
located inside the heater compartment and is set to
open at the temperature indicated in the Limit Con-
trol Setting Table 27. It resets automatically. The
limit switch operates when a high temperature con-
dition, caused by inadequate supply air flow
occurs, thus shutting down the heater and energiz-
ing the blower.
TABLE 27: LIMIT CONTROL SETTING
VOLTAGE
kW
TEMPERATURE LIMIT SWITCH Open Temp
º
F
5
1
140
7
1,3
140
10
1,2,3
140
15
2,4,6
140
1,2,3,4,5
140
6
150
30
1,2,3,4,5,6
150
5
1,2,3
140
7
1,2,3
140
10
1,2,3
150
15
2,4,6
140
20
1,2,3,4,5,6
150
1,3,5
160
2,4,6
150
7
2,4,6
140
10
2,4,6
140
15
2,4,6
140
20
3
160
30
3
150
10
2,4,6
140
15
2,4,6
140
20
5
160
30
5
150
20
30
230-3-60
460-3-60
575-3-60
230-1-60
