826081-XIM-C-0214
Johnson Controls Unitary Products
33
The ASCD is initiated on unit start-up and on any compressor
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 24.
Reset
Remove the call for cooling, by raising thermostat setting higher
than the conditioned space temperature. This resets any
pressure or freezestat flash codes.
Electric Heating Sequence Of Operations
The following sequence describes the operation of the electric
heat section.
Single-stage heating (7, 10, & 15 kW 460V heaters. All other
heaters MUST use a two-stage thermostat):
a. Upon a call for heat by the thermostat, the heater
sequencer (1S) will be energized. After completing the
specified fan on delay for heating, the UCB will energize
the blower motor.
b. The thermostat will cycle the electric heat to satisfy the
heating requirements of the conditioned space.
Two-stage heating (applies only to 20 and 30 kW heater 460V
heaters.):
a. Upon a call for first-stage heat by the thermostat, the
heater sequencer (1S) and contactor (2M) (20, 30 kW
460 volt) will be energized. After completing the specified
fan on delay for heating, the UCB will energize the
blower motor.
If the second stage of heat is required, heater sequencer
(2S) or contactor (3M) (20, 30 kW 460 volt) will be
energized. After completing the specified fan on delay for
heating, the UCB will energize the blower motor.
b. The thermostat will cycle the electric heat to satisfy the
heating requirements of the conditioned space.
Safety Controls
VOLTAGE
kW
TEMPERTURE LIMIT SWITCH
Open Temp
ºC[ºF]
7
2,4,6
58[140]
10
2,4,6
58[140]
15
2,4,6
58[140]
20
3
71[160]
30
3
65[150]
380/415-3-50
The control circuit includes the following safety controls:
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 Control Setting Table 19.
It resets automatically. The limit switch operates when a
high temperature condition, caused by inadequate supply
air flow occurs, thus shutting down the heater and
energizing the blower.
Reset
Remove the call for heating by lowering the thermostat setting
lower than the conditioned space temperature. This resets any
flash codes.
Heat Anticipator Setpoints
HEATER
KW
VOLTAGE
SETTING, AMPS
TH1
TH2
7
380/415-3-50
0.35
-
10
0.35
-
15
0.35
-
20
0.37
0.29
30
0.37
0.29
It is important that the anticipator setpoint be correct. Too high
of a setting will result in longer heat cycles and a greater
temperature swing in the conditioned space. Reducing the
value below the correct setpoint will give shorter “ON” cycles
and may result in the lowering of the temperature within the
conditioned space. Refer to Table 20 for the required heat
anticipator setting.
Gas Heating Sequence Of Operation
When there is a W1 call for heat, the heat relay (RW1) is
energized by the unit control board (UCB). The RW1-1 contacts
immediately close energizing the ignition control board (ICB).
The ICB checks the state of the flame sense circuit, the roll out
switch, the centrifugal switch and the primary / auxiliary
temperature limit switch circuit. If they are in the expected state,
then the ICB energizes the draft motor and verifies that the
centrifugal switch located on the end of the draft motor closes.
After the centrifugal switch closes, a 15 second heat exchanger
purging period is completed. After this purging period, the ICB
will simultaneously energize the pilot gas valve and the ignition
coil. Once the flame sensor senses a pilot flame is present, the
ignition coil is de-energized. The ICB checks for pilot flame
stability and once the ICB is satisfied that the pilot flame is
stable, the main gas valve is energized by the ICB. The UCB
will energize the indoor blower after a 45 second delay from the
call for heat. The ICB and UCB both monitor the furnace safety
devices during the furnace operation. When the call for heat is
Table 19: Limit Control Setting
Table 20: Electric Heat Anticipator Setpoints
