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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 ovens 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
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)
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.
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.
SECTION 3 - SERVICING COMPONENTS
Figure 23 - High limit control modules
(Shown in PS360-series oven)
United Electric Type 54
high limit control module
United Electric Type 55
high limit/cooldown
control module
Watlow high limit
control module
Reset button