A
DJM3
IOM-17
14 of 27 Mar 99 R3
OPERATION
DAY
/
NIGHT
OPERATION
The DJM3 supports a variety of fan, damper, and temperature control operating schemes. The exact
operation depends on the status of terminals “FS, HS”, and “K”. Night operation is not suitable for
100% make‐up air applications, due to the equipment having to open outside air dampers and heat
outside air. To operate in Night mode, a room thermostat or make/break reset must be used.
TABLE 12
Terminal Status
Blower
Operation
Damper
Operation
Control Source
Control
Mode
HS
FS
K
XXX
XXX
Off
On
Off
Off
Off
Constant
Off
Powered
N/A
Discharge/Room/BMS
Off
Day
Off
On
On
XXX
Off
On
On
On
On
Off
Intermittent
Constant
Off
Off
Off
N/A
Room
Discharge w/Room
Reset
Off
Night
Night
XXX = Switch (SW.) can be "ON" or "OFF"
FAN
CONTROL
In day mode, the supply air fan should run continuously (unless just starting the morning warm‐up or
tripped on low limit.). For supply fan operation, the discharge sensor must be operating correctly as it
is also used as the low limit sensor. If the discharge sensor resistance is too high (or open circuit), the
DJM3 perceives a low limit fault and locks off DJM3.
DAMPER
CONTROL
The inlet damper actuator(s) is enabled through output terminal DM2. The DJM3 has a delayed supply
blower start to allow time for the dampers to open.
BURNER
CONTROL
Burner is enabled when a valid heat call is made and terminal “HS” is powered. The DJM3 will enter a
heat exchanger purge cycle. When the purge cycle is complete, the DJM3 will run combustion blower
at light‐off speed and enable the ignition control to start the pilot. When the ignition control proves
pilot light‐off it will enable the main gas valve. Once the main flame is established and the DJM3
receives a feedback signal to terminals VFB24 or VFB120 and VN the control will modulate the gas
valve and combustion blower to satisfy the heat call. If the DJM3 does not receive the feedback signal
the alarm contact, terminal “AL”, will be activated.
When heat call is satisfied the DJM3 will cycle off the burner. The combustion blower will continue to
run for several minutes after heat call is open to maintain purge and cool off the burner and heat
exchanger.
