Service manual

A DJM3.2 MANUAL
status changes (on/off or off/on transition) or when the "SA" (supply air blower) contactor is energized or
FS status is changed to on/off.
A 30-second anti-noise low limit bypass timer is started every time a low limit condition is detected and
the 5-minute auto bypass timer has timed out. This timer is designed to prevent nuisance low limit lock
outs caused by any electrical noise which may be picked up by the discharge sensor. If the low limit
condition exists for more than 30 seconds, a low limit lockout will occur. When the low limit trips, the
DJM3.2 closes it's L/L 24 VAC output alarm contact. Also, LED 1 will be turned on steady. Flame
failure can also activate this output.
Whenever the discharge temperature is below 40°F but one of the bypass timers is operating, LED 1
will flash every 2 seconds. Also note that the low limit bypass timer is reactivated when terminal "K" is
cycled.
NOTE: For additional information see "Discharge Sensor Self Test" (Page 24).
Resetting Low Limit
To reset the low limit, turn the power off and on to the DJM3.2 control terminals "T1" and/or "T2"; or
interrupt power to terminals "FS, HS, and K" all at the same time. Most units can have the low limit
reset at the remote panel by turning the control switch off (often labelled fan or unit switch) and then on
as it will remove power to the "FS, HS, and K" terminals.
XI. DAY AND NIGHT OPERATING STRATEGIES
The DJM3.2 supports a variety of fan, damper, and temperature control operating schemes. The exact
operation depends upon the status of terminals “FS, HS”, and “K”.
Blower/Damper Operation
The combination of energized night (K) and fan (FS) terminals set the blower and damper operation at
night.
DAY (FS on, HS on) Continuous Blower, Dampers Open, Discharge Control
NIGHT (FS off, K on, HS on) Intermittent Blower, Dampers Off, Room Control
ALTERNATE NIGHT OPERATION Continuous Blower, Dampers Off, Discharge Control
(HS, FS, K terminals all energized) with Room Reset
Day and Night Operating Strategies
XXX = Switch (SW.) can be "ON" or "OFF"
Heat
SW.
Fan
SW.
Night
Term.
Blower
Operation
Damper
Operation
Control Source
Control
Mode
XXX
XXX
Off
On
Off
Off
Off
Constant
Off
Powered
N/A
Discharge
Off
Day
Off
On
On
XXX
Off
On
On
On
On
Off
Intermittent
Constant
Off
Off
Off
N/A
Room
Discharge/Room
Off
Night
Night
Day Mode General Heat/Blower Operation
OFF The first option in the above chart is "Off".
Day The second option applies to day operation.
If the discharge sensor is warm, the supply air fan will start in 30 seconds.
Page 8 Revised: 3/11/99