Midco Economite RE4400B / RE4400BA - Manual (Page 12)

Part 2 Service
PART 2 SERVICE
DANGER: Do not tamper
with the unit or controls. If
trouble occurs contact the
installing contractor, service
agency, or fuel supplier. See front
cover.
DANGER: Be sure that the
main and pilot manual Shut-Off
Valves are closed and the burner
power supply is turned off before
removing any parts for service.
CAUTION: Cover plates, guards, and enclosures must be maintained in place at
all times except during maintenance and service.
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The pilot is of the premix, blast type. The full force of blower air is brought into the mixing tube
where the proper amount of gas is added through the pilot orifice. This mixture is discharged
through the pilot. The mixture provides the flame that contacts the flame sensing rod and also
ignites the main gas.
CAUTION: Do not indiscriminately increase pilot orifice size. Pilot troubles are rarely
cured in this manner and new troubles may be created.
Under normal conditions, with a slight negative pressure in the combustion chamber, pilot
operating pressures should be set as indicated in Table 4.
Some conditions which may require a change from the normal setting include: extremely long
tubing connections between the regulator and pilot solenoid, high negative or positive
combustion chamber pressure, actual air shutter setting and altitude extremes.
Do not subject the pilot to an inlet pressure over 14.0"W.C. See Section VI PIPING for high
pressure gas.
To adjust outlet pressure, remove the seal cap for access to the adjusting screw. Turning the
screw clockwise will increase outlet pressure, counter clockwise will decrease outlet pressure.
The spark rod for a natural gas burner is welded to a round 1/2” perforated retention plate.
(The spark rod for a propane gas burner is welded to a round 1/2” solid retention plate.)
CAUTION: Make sure that the natural gas burner has the correct spark rod
retention plate before operating the burner. See “Replacement Parts Lists” if replacement
is needed. The 1/2” retention plate is centered in the 3/8” Tee pilot and is positioned so the high
tension voltage will arc to the inside of the 3/8” Tee pilot.(
See Figure 7A and 7B ).
The flame sensing rod must be positioned as shown in Figures 7A and 7B so that the Ignition
Control Module will detect a proper flame.
Both the spark and flame rods are current carrying conductors and, along with their
connecting wires, must be kept free of contact with conductive metal parts of the burner. Rod
insulators and wire insulators should be clean, dry and free of cracks.
Both the spark and flame rods are made from heat resistant alloys and can be expected to
have a long service life. They should be routinely inspected, however, for corrosion or loss of
metal.
The pilot air tubing must be kept free of kinks or inside obstructions and must be positioned
per Figures 7A & 7B, otherwise air flow could be reduced and adversely affect the pilot flame.
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CAUTION: BEFORE SERVICING, mark with a scribe line or measure opening of
air controlling shutter, so that it can be reset to its original position following servicing.
Cleaning of the blower wheel is usually the only service required. Need for cleaning is
indicated if the character of the flame indicates a deficiency of air. Motor cooling air vents (if
present) should also be cleaned at this time.
The motor and wheel are removed as an assembly. Disconnect the motor wires from the
motor terminal strip. Disconnect the motor conduit from the motor and remove the mounting
bolts.
The burner is equipped with a diaphragm type air pressure switch so as to prevent the burner
from firing if the blower wheel is not running at its operating speed. When the motor is off there
is no air pressure present to activate the pressure switch and in turn there is no power flow to
the Ignition Control Module.
To make a specific test of the interlock circuit:
1. Turn burner power OFF.
2. Turn Manual Gas Cock OFF.
3. Disconnect the motor wire from the terminal strip to keep the motor off.
4. Turn burner power ON and set the operating control to ON or thermostat to call for
heat. Verify there is 120VAC line voltage by using a multimeter. Check for 24V
between the Ignition Control Module 24V and 24V GND terminals.
Part 2
Service
X Motor Blower
Interlock
12
IX Pilot
6000
6000
6000
6000 3.0”
to
4.5”
W.C.
Model
RE 4 8 5 0 B A
R E 4 7 0 0 B A
R E 4 4 0 0 B
R E 4 4 0 0 B A 0.055”
0.055”
0.055”
0.055”
Table 4: Pilot Specifications
Gas
Orifice
Diameter
#54
Wire Drill
Approx.
Capacity
BTU/Hr. Pilot Gas Pressure
2.5”
to
3.5”
W.C.
Natural Propane