Service manual

A DJM3.2 MANUAL
C. Damper operation:
• Dampers are closed at night.
10. The DJM3.2 can be converted from standard to high turndown DJ burner simply by cutting a jumper
wire on the back of the control.
11. Can be used with up to a 0.6 HP combustion motor.
12. Easier burner set up.
13. To reduce ground isolation problems, optical isolation was added to the digital and BMS inputs (+
and
Β ).
14. There are many standard service and testing features. These include status indicating LED’s,
service pot, and temperature test points.
IV. WIRING
Power supply = 24 VAC @ 1.2 amps
The DJM (terminals T1 and T2) requires a separate isolated 24 VAC 30 VA class 2 transformer. This
transformer must be powered from the same phases that power the combustion blower transformer.
Power applied to the input terminals (HS, FS, and K) should NOT come from the above isolated
transformer on “T1” and “T2”. This second power supply can be from a grounded transformer, terminal
“N” being wired to the neutral "hot" side (which could be grounded), applied to terminals “HS, FS”, and “K”.
Remote wiring for all thermostats and set points should be run using a minimum 22 ga-shielded wire.
For runs over 150 feet, the use of 20 ga-shielded wire is recommended.
Try to keep high voltage wires such as those used on motors and spark ignition, separate from low
voltage wires, such as those used on speed sensors, temperature sensors, flame rod, etc. This is to
avoid “voltage cross-talk” (stray induced high voltage signals that can adversely affect electronic controls).
All DJM3.2 relay contacts are rated at 5 amps. The TRIAC output (combustion blower) will handle up to a
5/8 HP motor at 120 VAC.
V. OVERVIEW OF DJM OPERATION
It is of the utmost importance to realize that this control is designed to reduce hunting (temperature
swings). To accomplish this, the control does not respond quickly to rapid changes in the discharge
temperature or to rapid adjustment of the set point. If you expect to see the heat start or stop within
seconds of adjusting the set point, it may not occur. Changes can take up to 6 minutes to slowly move
to the newly selected setting. This slow control change prevents overshooting and the resultant cycling
of the burner.
Supply Fan Operation
Refer to the DAY/NIGHT section for a full description of supply fan operation schemes (Page 8).
• 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 DJM3.2
perceives a low limit fault and locks off DJM3.2.
Damper Operation
Refer to the DAY/NIGHT section for damper operation. It is possible that the damper operation may be
independent of the DJM3.2 in many applications, thus the above noted section would not apply.
The Basic Burner Operating Scheme
1. Heat doesn’t run until there is a valid heat call and all the required heating operating conditions
Page 3 Revised: 3/11/99