Middleby Marshall PS224 PS310 manual Section Sequence of Operation, GAS Oven Sequence of Operation

SECTION 1 - SEQUENCE OF OPERATION

SECTION 1

SEQUENCE OF OPERATION

I.GAS OVEN SEQUENCE OF OPERATION

A.Electrical Supply

Gas heated ovens operate on 208/240V, single phase. Standard incoming power configurations are:

1.4-wire system (PS200 series, PS310/360 series, PS570, PS570S) - 2 single phase 208/240V sup- ply (hot) lines, 1 neutral and 1 ground.

2.3-wire system (PS360WB70, PS360EWB, PS555, PS570G, PS536) - 2 single phase 208/240V sup- ply (hot) lines and 1 ground.

For all wiring configurations, the voltage when measured from either hot line to neutral should never exceed 130V.

B.Door Switch

Closing the control cabinet door (or machinery com- partment door, as appropriate for the oven model) will close the door switch and allow the oven to operate.

Note that the electrical systems will still be “live” if the switch is open, although the oven cannot operate.

The door switch has a bypass position to enable ser- vice operation with the door opened. When the door is open, grasp the switch actuator and pull it out as far as possible. This will close the door switch and permit troubleshooting. Closing the control cabinet door will reset the switch.

1.Closing the door switch permits a circuit to go through a fuse (or circuit breaker, as appropriate for the oven model) to one side of the conveyor switch, blower motor switch, cooldown relay and heat switch.

2.Closing the door switch permits a circuit to go through the motor fuse (two 9A or 15A fuses per motor).

C.Conveyor Switch

Closing the conveyor switch permits a circuit to go to the Conveyor Speed Control Module, which:

1.Sends power to the gear motor (conveyor drive mo- tor). The 120VAC signal to the Conveyor Speed Control Module is rectified to a 90VDC signal which is then sent to the gear motor.

2.Allows regulation of conveyor speed. Adjusting the thumbwheel (or digital pushbutton display unit, as appropriate) to the desired conveyor belt speed in- structs the Conveyor Speed Control Module to regu- late the output to the gear motor. This increases or decreases the conveyor speed as necessary to match the speed setting shown on the thumbwheel or display unit.

D.Blower Switch

Closing the blower switch energizes:

1.The cooling (axial) fan(s).

2.The blower motor contactor (s).

Closing this contactor starts the blower motor(s). When both blower motors are up to speed, centrifugal switches located inside the blower motors (or air switches de- tecting blower operation, as appropriate for the oven model) will close, setting up the heat circuit.

3.The Temperature Controller.

E.Heat Switch

Closing the heat switch completes a circuit:

1.Through the heat switch.

2.Through the blower motor centrifugal switches (or air switches, as appropriate for the oven model).

3.Through the high limit switch.

4.One circuit then goes to the:

a.Burner (L1).

b.Transformer (110V to 24V).

c.Motor relay coil. On a cold start the heater on this relay takes about 30 seconds to warm up before the relay will energize. This gives an additional prepurge. The relay is not used on ovens with 208/240V burner blower motors.

d.Burner blower motor. As the motor reaches full operating speed, the centrifugal switch (or air flow switch, as appropriate for the oven model) closes and applies voltage to the burner con- trol. This energizes the ignitor control spark transformer and the pilot valve. The spark then lights the pilot. The flame sensor proves the presence of the pilot flame, and the ignitor con- trol then shuts off the spark. At the same time, the main burner valve is opened. The main burner is then ignited.

If the pilot does not light within approximately 90 seconds, the oven will shut down.

The pilot and main gas valve will stay on (open) as long as the heat switch is ON and the flame is proven. If the flame goes out for any reason, the pilot will try to light for 90 seconds, and then go into automatic lockout. To relight the pilot after it has gone into automatic lockout, the burner must be turned OFF for 5 minutes and then turned ON again.

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