Service manual
A DJM3.2 MANUAL
If the heat switch is on and there is an immediate heat call or a heat call within the first
minute of the blower starting, the blower will shut off or remain off until the burner has
been running for 30 seconds.
If during this time the heat call is lost, the blower will cycle back on but the pre-purge
will continue (Under some conditions, the supply fan may cycle a few times before the heat
starts).
If there is a heat call and the heat switch is off, and the discharge temperature is not
below 40ºF, the DJM3 will ignore the requirements for having the burner on before the
supply blower is started.
If the discharge temperature is below 40ºF and the heat switch is off, the DJM3.2 will
not start the blower until the discharge sensor rises above 40ºF and the low limit is set
in the activated position (dipswitch 8 "on"). Note that this assumes the low limit bypass
is still timing. If the low limit bypass has timed out the DJM3.2 will lock off on low limit.
Night Mode General Heat/Blower Operation
For night operation, the last three options on the above chart could apply depending on unit wiring and
DJM3.2 configuration.
• Control Source from Room (see above chart).
• The DJM3 must have a room thermostat connected to it.
• If it is a
modulating room thermostat it will be wired to the DJM3 terminals “V, X, Y”, and “Z”. If the
night time room temperature drops 1.5ºF below the night room set-point, the heat will be brought
on and kept on until the room temperature rises 1.5º over the room set-point. During this time, the
burner will fire at maximum rate until the room temperature is satisfied or the discharge
temperature is becoming too hot. The internal modulating high limit will act to prevent the
discharge temperature from exceeding 120ºF.
• If using a make/break room thermostat (usually “X” and “Z”), when it calls, the DJM goes to pre-
purge, starts heat, fan starts, if heat at discharge air sensor exceeds 120ºF it turns off heat. If heat
is removed from sensor fast enough, the burner restarts and cycling at about 120ºF discharge
continues. If heat is not removed quickly from sensor (such as low air flow) then the S/A fan shuts
down one minute after the heat cycles off.
• In nighttime operation the supply air fan will start about 30 seconds after the heat starts. The
supply air fan will stop about 60 seconds after the heat goes off. After the heat call is finished, the
combustion fan will run for about one minute in the cool down mode (to cool the heat exchanger).
Depending on the position of dipswitch 3, and the required control source (see above chart), the room
thermostat can be made to operate in the following manner:
• With dipswitch 3 "on" the DJM3 operates as discharge control WITH room reset during the
day when the blower is operating continuously. At night when operating from the room thermostat,
the blower is operating intermittently. (Dipswitch 3 on.)
• With dipswitch 3 "off" and the control in "day" operation (no power on terminal “K”), the DJM3
operates only on Discharge Control. There is no room reset being allowed from the room
thermostat. (The supply fan operates continuously during the day.)
• At night the room thermostat operates as a room control if the heat ("HS") and night ("K") terminals
are activated on the DJM3. The supply fan will be operating intermittently and will be turned on by
the DJM3 after the room thermostat calls for heat. During intermittent blower operation, the supply
fan blower will start 30 seconds after the burner fires up and shut off 60 seconds after the burner
stops firing. The combustion blower will run for 60 seconds after the flame is turned off to assist in
cooling down the heat exchanger.
• Lower Set-point at Night - If room reset is required during the day at one set-point, and at night
room control is to be at a lower set-point, a separate night thermostat and/or set-point dial must be
switched by an external relay.
Page 9 Revised: 3/11/99