DJM2.4 MANUAL
18 Oct 00 R2
Refer also to “Water and Ice from Combustion” on page 32 regarding another problem with
improper combustion set up.
High Turndown (Rectangular) Burner
HIGH FIRE SET UP
1. Place a jumper across the DJM2.4 terminals “SV and SR” to force the control into a
manual firing mode.
2. Set manual firing pot labelled “SER” (Pot 4
located near the middle of the panel) to high
fire by turning it fully clockwise. Ensure adequate inlet fuel pressure. Adjust the high fire
manifold pressure to that listed on the rating plate. Adjust the combustion air slider or
inlet damper until the high fire O
2
reading is between 3.5 and 4.2%. Tighten the locking
screw to keep the damper locked into this spot.
Add another locking screw if the damper moves from its position.
LOW FIRE SET UP
For both 10:1 and 15:1 turndown burners.
NOTE: Most high turndown DJ units will employ one of the following Maxitrol
modulating DC volt gas valves.
Series 20 - M520, M620. These valves do not have high fire regulators. High fire
pressure is set up at the appliance regulator.
Series 50 - M550, M650, ES350. These valves do not have high fire regulators. High fire
pressure is set up at the appliance regulator
ES345D-L This valve has a built in high fire regulator. Used on DJ140
models
The above valves differ from each other in size, configuration, BTU capacity, physical layout, and
low fire set up.
Check the unit you are working on to verify what type of modulating gas valve you have to ensure
the correct combustion set up method is used.
Top Loading - Ensure that there is a ¼" aluminium tubing connected from the top of the
modulating gas valve vent connection to the burner box. This is to guarantee that the varying
burner box pressure allows the proper flow rate through the modulating gas valve. Also ensure
that the small vent hole under the oval shaped cover is sealed off with silicone or Tremco tape.
When doing combustion analysis it is important that the top of the valve be sealed by either
reinstalling the cap after each adjustment, or placing your finger fully over the top to seal the
open top on the valve. The reason for this requirement is that the valve is “top loaded” which
means that the valve is having pressure from the combustion fan added to the top of the valve’s
diaphragm thus increasing the gas flow through the valve, especially at higher flow.
Series 20/ M520 and M620 (High Turndown)
As these valves have 2 low fire adjustments the following procedure should be followed
carefully:
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