Service manual

A DJM3.2 MANUAL
NOTE: There is an optional room thermostat operation using a standard make/break
thermostat for room sensing in place of the modulating control. For information
on this option refer to this guide under "Make/Break Thermostat operation".
XII. BASIC BURNER OPERATION
The following controls the DJM3 burner:
• If the DJM3 is not satisfied, it calls for heat.
• Contacts 4-2 close to energize the flame supervision control.
• The flame supervision control starts the pilot. If it is a good pilot it opens the main gas valve and
sends a feedback signal to the DJM3 terminal 3.
• The DJM3 can now shut off the pilot as it controls the burner modulation and combustion fan
speed.
XIII. TEMPERATURE CONTROL – GENERAL OVERVIEW
The DJM3 is primarily a “discharge air control” but has the optional capability of electronically changing
the “calculated set-point” if external reset devices are wired correctly and the appropriate dipswitches
are configured correctly. The “calculated or operating discharge air set-point” is the mathematical
addition of the master set-point and one optional reset signal. The reset signal may be from room
temperature, ambient temperature, voltage, or current input. The voltage and current inputs will only
reset the discharge air calculated set-point (SPC) in the up direction. The room and ambient
temperature resets will reset SPC in both directions.
The only exception to “discharge air control” is when the DJM3 is wired to provide space temperature
control at night (OPTIONAL). During this night time operation the discharge sensor acts as a
modulating high limit and prevents discharge air temperature from exceeding 120ºF.
The DJM3 has proportional and integral (PI) control. On initial start-up, it is designed to bring the
discharge temperature quickly to within 10ºF of the calculated set-point. After this initial start-up time,
small output corrections to the gas valve are gradually made until the discharge air temperature is
within ±1.5ºF of the “calculated” set-point. When the heat load is light and the burner is cycling
between low fire and off there will be some temperature swing. This is especially true for the standard
(round) burner, as it is limited to a 2.5:1 turndown ratio. (This means that a heat exchanger designed for
100ºF-temperature rise will have a temperature rise of 40ºF at low fire, thus it must cycle the burner often.) Low
load operation is inevitable and the burner on/off control algorithms have been improved to provide 20
to 40% better temperature control than was possible with the original DJM.
XIV. MASTER SET-POINT
As a SET-POINT, the DJM3.2 is designed to use either:
• The set-point mounted on the face of the DJM3 (range of 10-35ºC or 52-95ºF). If the DJM3 face
mounted set-point is used, terminals “SP and S” must be jumped; or
• The Johnson TE 6100-960 set-point (range of 50-85ºF and usually remote mounted). If the TE 6100-
960 is used as a set-point, “S to SP” is not jumpered and the TE 6100 must be wired:
TE 6100 Wires DJM3.2 Terminals
Violet (not used, sensor)
Blue
M
Orange
S
Grey
U
Red (not used)
Q
(No jumper S-SP)
P
TE 6000 Sensor
Page 10 Revised: 3/11/99