Middleby Marshall PS220 III. High Limit Control Module, Operation and Troubleshooting, Location

III. HIGH LIMIT CONTROL MODULE

On most PS200-series and PS300-series gas ovens, the temperature controller monitors the high limit. All other oven models use a High Limit Control Module that is inde- pendent of the temperature controller.

Middleby ovens have used several different types of high limit control modules. See Figure 23.

•The United Electric Type 54 control was used for high limit functions only. Ovens equipped with this control did not have a cooldown feature. The control was used on early PS310 and PS360 electric ovens.

•The United Electric Type 55 control included both high limit and cooldown functions, and was used on PS310 and PS360 electric ovens.

•The Watlow high limit control module is the only ver- sion still in use by Middleby. The module includes high limit functions only. The cooldown function is con- trolled by the oven’s temperature controller, except on PS200VL-series ovens, which do not include a cooldown feature.

The Watlow high limit control module is used on PS200- series, PS360-series, and PS555/570-series ovens.

Service information in this Manual is limited to the current Watlow high limit control module. The United Electric units are no longer available. Service Kit P/N 39733 can be used to upgrade either of the two previous controllers to the Watlow version.

A.Part Number Reference - High Limit Control Mod- ules

P/N Description

28071-0002 United Electric Type 54 high limit control module No longer available - upgrade to current model 34982 using Service Kit 39733

SECTION 3 - SERVICING COMPONENTS

C. Operation and Troubleshooting

Refer to the wiring diagrams at the back of this manual for high limit wiring connections.

The Watlow high limit control module generally uses a dedi- cated high limit thermocouple. Some older ovens use a dual-function, four-lead thermocouple that sends a signal to both the temperature controller and the high limit control module. Refer to Thermocouples on Page 54 for details.

If the temperature sensed by the high limit thermocouple exceeds 650°F/343°C, the high limit control module will shut down the oven and illuminate the green reset button. The module will need to be reset (by pressing the reset button) before the oven can be operated. The reset button is located inside the machinery compartment to ensure that it is reset by an authorized service agent. The agent should determine and correct the cause of the high limit condition before returning the oven to service.

An open high limit thermocouple will trigger the high limit control module to shut down the burner. The high limit control will need to be reset after the open is corrected (as per the procedure described above) before the oven can return to operation.

Figure 23 - High limit control modules

(Shown in PS360-series oven)

United Electric Type 54 high limit control module

28071-0014 United Electric Type 55 high limit/cooldown con- trol module

No longer available - upgrade to current model 34982 using Service Kit 39733

34982 Watlow high limit control module, 115V

For use on ovens with 120V control circuits

33983 Watlow high limit control module, 240V

For use on ovens with 208-240V control cir- cuits

30693 Illuminated reset button (green) for Watlow con- trol (all voltages)

United Electric Type 55

high limit/cooldown

control module

39733 High Limit Conversion Kit for PS300, PS310, PS350, and PS360 ovens

Replaces P/Ns 28071-0002 or 28071-0014 with

P/N 34982

B. Location

On ovens that include the separate high limit control mod- ule, it is located:

• PS200-series - Inside the machinery compartment.

• PS360-series - Inside the control compartment.

• Early PS555 ovens - Inside the left blower motor com- partment.

• Current PS555 and all PS570 ovens - Inside the machinery compartment.

45

Watlow high limit

control module

Reset button