Service manual

A DJM3.2 MANUAL
Low Limit Lockouts
NOTE: If your application does not require it, L/L could be disabled. If there is an
intermittent problem with the discharge sensor, a false low limit lock out code
may be generated. This happens if the discharge sensor generated an initial
lockout and then the reason for the sensor lock out disappeared. (Refer to Section
X for more detail on the low limit.)
If the discharge sensor calibration is not correct you can also have low limit lockouts.
Also, be aware if the heat call light comes on, the burner lights, and there is not adequate heat to
allow the discharge temperature to rise above the 40ºF. Low limit setting for the period of time that
the low limit is being bypassed, and then the low limit light will come on when the unit locks off. If the
low limit sensor then warms up, both the heat call and low limit light should remain on until someone
resets it by turning the power off to the DJM3.2. We strongly recommend that no one reset the
control until the status of all of the troubleshooting lights are recorded.
Items that will turn off other alarm lights when low limit light is activated:
What happens if ignition fails on morning start-up?
On a Warm Day
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•
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Dampers open
Supply fan starts
If heat call light comes on:
 Supply air fan is shut off (assumes first call must be delivering cold air into building).
NOTE: If this occurs during the first 36 seconds of morning startup, the supply fan
would stay off.
 Dampers go closed.
 Combustion fan starts, purge light comes on.
 Purge cycle completes, purge light goes off.
 Ignition enable light comes on.
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•
•
Now, if ignition failure occurs:
 Ignition enable light flashes 90 sec. later.
 Combustion blower turns off.
 Low limit light will come on if discharge sensor falls below 5ºC (40ºF).
 Sensor or ignition light that was flashing will go off when low limit light goes on.
On a Cold Day
If discharge sensor is in warm area:
 Dampers will open.
 Supply fan will start.
 Fan and dampers may go off due to low limit if discharge sensor cools.
 Ignition attempt as above.
If discharge sensor is in a cold area:
 Dampers open, fan awaits response that heat is on.
 Ignition attempt as above.
 Supply fan may start and run on low limit bypass until flame failure light comes on.
 Then dampers, supply fan and combustion fan shut off.
 Only LED 4 flashes at one-sec interval – FLAME FAILURE.
In any of the above three situations, assuming that the original problem did not rectify itself you will
Page 35 Revised: 3/11/99