Dometic RM3962, Service Manual

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17
7.4 Burner
7.5 Flue Baffle
Any reading below 20 millivolts could cause erratic gas
operation. note: A reading of 20 or less could be caused
by low gas pressure, carbon build up or improper ther-
mocouple location. The thermocouple should be centered
over the burner and extend over 3 slots. The control board
reads negative millivolts from the thermocouple and the
positive lead goes to the ground terminal on the control
board. The lower control has a built-in delay when the
unit is first turned on. If the lower control reads millivolts
in excess of 6 MVDC the control will go into a 30 second
gas delay before attempting to light on gas. To test the
thermocouple set the meter to DC millivolts. Put the black
lead from the meter to terminal J4 and the red lead from
the meter to J10 or ground ( other lead from thermocou-
ple). Start the unit on gas and measure the DV millivolts
produced by the thermocouple. The thermocouple should
produce 22 to 36 millivolts within 45 seconds. If the milli-
volts are 20 or below erratic operation will occur. Anything
below 10 to 13 the control board will not keep the gas
valve energized and turn on the check light after the third
trial-for-ignition. Approx 6 to 7 minutes.
The slots in the burner should be directly below the flue
tube. The burner should be cleaned periodically, at least
once a year. Soak the burner in an alcohol based solvent
and allow to air dry. If the burner does not have a good
ground it can cause erratic gas operation. The electrode
sparks to the burner tube and a erratic ground will cause
erratic gas operation.
The flue baffle ( spiral baffle ) is a twisted piece of metal
that hangs in the flue tube to slow the heat from the flame
to the proper location on the cooling unit. If the flue baffle
is too high or low the heat will not be transferred to the
cooling unit properly.
MODEL ABOVE
BURNER
SIZE
RM3762 1-7/8 5-1/8X13/16
RM3962 1-7/8 5-1/8X13/16
Lack of heat transfer to the cooling unit will cause low cool-
ing performance in the gas mode. It should be cleaned
periodically, at least once a year. The proper position of
the baffle above the burner should be as shown in the
chart : always refer to parts list on the model/product
number unit you are currently working on.
7.6 flue tube
The flue tube is welded to the boiler of the cooling unit. As
heat travels up the flue tube and slows at the flue baffle it
transfers heat to the cooling unit. Carbon build up will not
allow the heat transfer to the cooling unit and cause lack
of cooling on gas. In a ruff riding coach there has been
rare cases where the weld will crack and create lack of
heat transfer to the cooling unit. The flue tube must be
cleaned periodically, at least once a year. Clean by using
a flue brush, Dometic Part no. 0151404001.
Baffle
flue tube
Flue Baffle
Burner