DJM2.4 MANUAL
28 Oct 00 R2
Combustion blower runs at light off speed unless power is turned off.
If an external low limit is on the unit and it trips it will shut off the fan and the dampers,
and usually leave power to the DJM although some units are designed to lock the DJM off
also.
In either of the above situations, assuming that the original problem did not rectify itself you
will have the supply fan off, the combustion fan on and the low limit tripped when you arrive at
site. If you turn the unit service or remote on/off switch off for 30 seconds and then turn it back
on, watch the lights as the ignition process retries. If the ignition or sensor problem still exists it
should be evident within a few minutes.
Night Heat Function Problem When Slaved From C-TRAC
On the odd occasion when a night heat function is applied to a DJM that is slaved to a C-TRAC
the following operation has been observed:
- Room stat calls for heat through the C-TRAC
- The C-TRAC outputs a heat call to the DJM and it completes firing the burner
- The auto fan switch starts the unit supply air fan
- Now the problem begins
- In a short time after the supply fan starts the auto fan switch cools and the fan shuts
off
- The DJM during this time has modulated to low fire
- There is not enough heat produced to remake the auto fan switch, the DJM may
continue to modulate at low fire depending on temperature conditions at the
sensors.
- Suggested resolution:
- When C-TRAC terminal “K” is powered at night the coil of a relay is powered.
- The contacts of the relay are located between the DJM main gas feedback terminal
and the coil of a camstat. The contacts of the camstat parallel the auto fan switch
contacts.
- Only at night and when the burner is in operation does the camstat have power to
start the supply fan and it will keep it in operation until after the heat call is
completed and the camstat has timed out.
Ignition Problems
Check the condition of the pilot assembly. Check for damaged or dirty ceramics, proper gasket,
and pilot set up. If you are still having problems lighting the burner, check the items itemized
below.
If you have been having problems lighting the burner, check the following items:
1. If the combustion fan wheel or motor have been changed refer to the diagram just before
section XVI below.
2. If the combustion has been set up, the ignition should be checked. Whenever the total air
slider has been adjusted it affects how much air flows into the pilot air tube.
3. Occasionally some ignition control devices have the power to throw a spark through the
To Next Page
Loading...
