Midco Unipower A-Series - Manual (Page 10)

Part 2 Service
CAUTION: Do not tamper with the unit or controls. If trouble occurs contact your
serviceman.
CAUTION: Be sure that the main and pilot manual valves are closed and the burner
power supply is turned off before removing any parts for service. Do not push relay
contacts in manually.
■ ■ ■ ■ Maintenance of the burner box and nozzle is minimal, due to the simplicity of the parts and
the absence of small air or gas passages. An occasional inspection of the parts in contact with the
flame will suffice. The burner nozzle parts should show no severe loss of metal or warping.
■ ■ ■ ■ If the burner mounting flange shows evidence of overheating, check the tightness of the
burner mounting. The burner is intended to be sealed into the appliance face as shown in Figure
4 to prevent blow-back of hot flue products around the nozzle and flange.
■ ■ ■ ■ The pilot is of the premix, blast type. Undampered blower air is brought into the pilot body
through the air orifice where the proper amount of gas is added through the pilot gas orifice. The
mixture is discharged through the alloy flame retention pilot tip. The pilot is rated for an
approximate capacity of 20 MBH and a normal operating pressure of 2.5" to 4" W.C. for both
Natural Gas and Propane.
■ ■ ■ ■ The pilot regulator is factory set for an outlet pressure of about 3 1 /
2
" W.C. which will be
suitable for average conditions. Do not indiscriminately increase orifice sizes. Pilot troubles are
rarely cured in this manner. Adjust the pilot as described in the start-up instructions included with
the burner.
■ ■ ■ ■ The spark rod is located on the center line of the pilot and is arranged to arc to the inside of
the central port. Spark current is supplied by a 6000V, 20 milliampere (minimum) end point
grounded ignition
transformer.
■ ■ ■ ■ Service of the pilot
will generally consist
only of inspection and
cleaning. Check that the
air tube, pilot body and
the tip ports are free of
lint and dirt and that the
pilot tip is free of serious
corrosion. The spark rod
insulator must be clean,
dry and free of cracks.
See Figure 13.
■ ■ ■ ■ The high tension
cable for the spark
electrode should be
checked for cracks and
abrasions.
■ ■ ■ ■ Proper operation of
the flame safeguard
depends on a reliable
current flow through
the flamerod, pilot
flame and the burner
frame. The flamerod
must be free of any
contact with conductive
burner parts. The
insulator must be clean, dry and free of cracks. While the rod is made of heat resistant alloy, it
may eventually deteriorate at the point of flame contact and should be replaced if it is seriously
corroded.
X Pilot and Flame Sensor
IX Burner Box and
Nozzle Assembly
Model A50G
Air Orifice
Natural
Propane
5 /
16
" (Brass)
#45 (.082) #47 (.078)
#50 (.070)
Pilot Orifice Sizing
9 /
32
" (Aluminum)
A52-A55G A73-A77G
C
L
Figure 13: Pilot Assembly
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