Middleby Marshall PS570 manual Air shutter adjustment, Temperature, Pilot Application, Air Shutter

Temperature

Ignition controls should not be exposed to tempera- tures exceeding 140°F (60°C) or less than -40°F (-40°C).

Pilot Application

The pilot and flame sensor application is the most criti- cal aspect of the llD application.

The pilot flame must make contact with the pilot tip and surround the flame sensor probe. A multimeter or ampmeter set to read microamps (mA) is necessary to verify that the proper amount of current is being main- tained through the pilot flame. The minimum value required is 2.0 mA. Rectification-based ignition sys- tems respond in less than 0.8 of a second to a loss of flame. If the minimum signal is not being maintained at all times, OR if the pilot flame is briefly directed away from the flame sensor or pilot tip, the main gas valve may cycle rapidly (“chattering”) or the burner may be prevented from activating.

Other conditions that can cause the failure of the main burner to activate, OR chattering of the burner, are:

1.Pilot flame is too small.

2.Gas pressure is too low for proper pilot flame im- pingement on the flame sensor.

SECTION 3 - SERVICING COMPONENTS

In these cases, the pilot may ignite, but the main burner gas valve will not be energized. It is also possible for drafts or unusual air currents to deflect the pilot flame away from the flame sensor. Deflection of the pilot flame may also be caused by main burner ignition con- cussion or roll-out of the main burner flame.

An additional point to be considered is the condition of the pilot flame. If the pilot flame is hard and blowing, the grounding area of the pilot is reduced to a point where the necessary current is not being maintained, and a shutdown of the system will result.

The positioning of the flame sensor is also critical in the pilot application. Positioning of the flame sensor should be such that it will be in contact with the sec- ond, or combustion area of the pilot flame. Passing the flame sensor through the inner cone of the pilot flame is not a recommended procedure. For this rea- son, a short flame sensor may provide a superior sig- nal over a longer one. The final determination of the sensor location (length) is best determined by the use of a multimeter set to read microamps (mA).

E.	Burner Blower Motor
The burner blower motor is located on the side or top of the
burner housing. Some blowers use a flexible tube to con-
nect the blower to the burner, depending on the available
space inside the machinery compartment. The burner
blower motor drives a blower wheel located in a housing
attached to the end of the motor that is the primary air
supply for combustion. The motor requires no lubrication.
Depending on the oven model, the burner motor operates
on either 120V or 208/240V (line voltage). 120V motors
have an internal centrifugal switch that controls the 24V
power supply to the gas valve (see Burner Blower Motor
Centrifugal Safety Switch on Page 80). 208/240V motors
use a separate air pressure safety switch to sense blower
operation (see Air Pressure Safety Switch on Page 81).
This safety feature prevents burner operation in case of motor
failure.
F.	Air Shutter
The air shutter is a round metal plate located on the open
end of the burner blower wheel. Adjusting the position of
the shutter will increase or decrease the amount of air that
is permitted into the plenum for combustion. Rotate the
plate in a counterclockwise direction to increase the air
supply, or in a clockwise direction to reduce the air supply.
You can insert a drill bit into the shutter gap to check the
size of the opening. Refer to Figure 69 for the recommended
opening sizes.
Early Midco burners use an adjustment screw on the front
wall of the plenum to adjust the airflow. If it is not possible
to adjust the air supply properly using the screw, a retrofit
kit is available (P/N 36829) to install the external air shutter		95
shown in Figure 69.

Figure 69

Air shutter adjustment

Wayne burner

Standard openings:

•1/4”/6.4mm for natural gas ovens

•3/8”/9.5mm for propane ovens

	Loosen hex	Counter-
Clockwise -		clockwise -
	nut to adjust
less air		more air
	shutter

Midco burner

Standard opening 5/16”/7.9mm (all gases)

Clockwise -		Counterclockwise -
less air	Loosen	more air
	screw to
	adjust
	shutter