Middleby Marshall Understanding Conveyor Motor and Safety Switch Features

SECTION 3 - SERVICING COMPONENTS

VI. BLOWER MOTOR CENTRIFUGAL SAFETY SWITCH (PS360-SERIES)

Middleby ovens have a safety feature that prevents the burner/heating elements from activating if the blower(s) are not in operation. On PS360-series ovens, this feature is controlled by a centrifugal switch mounted inside each blower motor. If either motor is not operating, the burner/ heating elements cannot activate.

The centrifugal switch is a normally-closed (NC) limit switch mounted inside the rear of each blower motor. See Figure

49.When the motor is not running, the centrifugal switch weight holds the switch open. As the motor reaches full speed, the weight moves away from the switch permitting the contacts to close. When the switch contacts of BOTH blower motors are closed, the heat circuit is completed, allowingthe burner/heating elements to activate.

If a blower motor is not operating, the switch will not close and the circuit remains open, preventing burner/heating el- ement activation.

A.Part Number Reference - Blower Centrifugal Switch

On all PS360-series blower motors, the centrifugal switch can be replaced with switch P/N 27270-0144.

B.Troubleshooting

1.To access the switch, remove the rear motor wiring cover plates. See Figure 49.

2.When the switch is operating properly, both sides of the brown wires coming from the switch should be “hot” when the motor is at full RPM.

3.No adjustment can be made to the switch. If it is not operating properly, it must be replaced.

VII. BURNER BLOWER MOTOR CENTRIFUGAL SAFETY SWITCH (PS200-SERIES GAS, PS310, PS314, PS360, PS360WB, PS570S)

Middleby gas ovens with a 120V burner blower motor have a centrifugal safety switch that prevents burner activation if the burner blower motor is not in operation. This includes:

•Most PS360-series ovens (except PS360WB70 and PS360EWB);

•PS200-series gas ovens (except units produced with the modulating gas system);

•All Model PS570S ovens.

Ovens with a 208/240V burner blower motor use a separate air pressure safety switch to prove motor operation. See Air Pressure Safety Switch on Page 81.

The centrifugal switch is a normally-closed (NC) limit switch mounted inside each blower motor. When the motor is not running, the centrifugal switch weight holds the switch open. As the motor reaches full speed, the weight moves away from the switch permitting the contacts to close. This com- pletes the heat circuit, allowingthe burner to light.

If the burner blower motor is not operating, the switch will not close and the circuit remains open, preventing burner activation.

No adjustment can be made to the switch. If it is not oper- ating properly, the burner blower motor must be replaced.

Figure 49 - PS360-series blower motor centrifugal safety switch

Switch

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