Service manual

A DJM3.2 MANUAL
NOTE: If combustion is not set correctly it can result improper burning which may
produce products of combustion that smell, carbon and or an excessive amount
of water in the flue. Care should be taken to set burners up properly. Note that
temperature of the air and fuel may have a great affect on the set up you select.
If both the combustion air and the fuel are at a constant temperature throughout
the heating season, once combustion is set it should remain similar through the
season. However, this usually only occurs on indoor units. Setting up an outdoor
unit is not the same as setting up a unit or a boiler inside a building.
When a unit is located outside, it is subject to different temperatures of combustion air and fuel
through the season. These temperatures affect the densities, thus affecting the resulting combustion
process. In some instances units that operate with 3% oxygen at Β40º ambient temperatures will be
found to operate at 9% oxygen on an 80ºF day. How the gas line is run (indoors or across the roof) is
the largest contributor to this problem.
It is better to have a burner that runs clean and doesn’t produce a lot of water from the flue
throughout the season then to set up for best efficiency. Also, we recommend that the probe for
combustion analysis be placed directly into the heat exchanger outlet rather then in the flue. This is
because air can enter into the bottom of the flue and dilute readings in the flue.
Refer also to “Water and Condensation from Combustion” on Page 42 regarding another problem
with improper combustion set up.
High Turndown (Rectangular) Burner
High Fire Set Up
1. Turn on the service switch (dipswitch 5).
2. Set manual firing Pot Hi Service (located next to the + terminal) to high fire. Adjust the high fire
input to the correct clocked rate. Adjust combustion air slider or inlet damper until the high fire
O
2
reading is between 3.5 and 4.2%.
Low Fire Set Up
• For both 10:1 and 15:1 turndown burners.
NOTE: Most high turndown DJ units will employ on of the following Maxitrol modulating
DC volt gas valves.
Series 20 420, M520, M620. These valves do not have high fire regulators. High fire pressure is
set up at the appliance regulator.
Series 50 550, 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. Often 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 3" 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,
Page 30 Revised: 3/11/99