Market Forge 2400HE Service Manual

SERVICE & PARTS MANUAL

Supplement to

17-0393,

for

SUPPLEMENT

Cook & Hold for Power Saver II

Convection Ovens

Models:
2400 HE

2492 HE

MARKET FORGE CANADA LTD.

Mississauga, Ontario, Canada

Form No. 17-0406 Printed in U.S.A.

Power Saver II Ovens equipped with

Cook & H old Controls.

35 Garvey St., Everett, MA. 02149

Tel. [phone], Telex 94-9414, Cable MAFORCO

TABLE OF CONTENTS

SECTION

3

PRINCIPLES OF OPERATION

Paragraph

SECTION 1 INTRODUCTION
11 Description 1-1
12 Basic Functioning 1-1
13 Service 1-1
SECTION 2 OPERATION
21 Operating Controls and Indicators 2-1
22 Operating Procedures 2-1
221 Preheating 2-1
222 Cook Mode Operation 2-1
223 Cook & Hold Operation 2-1
SECTION 3 PRINCIPLES OF OPERATION
31 General 3-1
32 Theory of Operation 3-1
321 Power and Heating

Element Operation 3-1
322 Cook Mode Controls 3-1
323 Cook & Hold Mode Operations 3-2
33 Electrical Circuits 3-3
331 Power Circuit Components 3-3
332 Control Circuit Components 3-3
SECTION 4 TROUBLE-SHOOTING
41 General 4-1
42 Trouble-Shooting Guide 4-1
43 Electrical Fault Isolation 4-1
44 Electrical Trouble-Shooting

Procedures 4-5

Page

Paragraph

441 Trouble-Shooting Sequence 4-5
442 Incoming Power 4-5
443 General Oven Test 4-5
444 Transformer (440/480

volt service only) 4-5
445 Circuit Breaker 4-6
446 Power ON-OFF Switch 4-6
447 Door Switch 4-6
448 Operating Thermostat Control 4-6
449 Selector Switch 4-7
4410 60-Minute Timer and Buzzer 4-7
4411 Fan Motor and Mini-Relay

for 440/480 Volt 4-7
4412 Heater Contactors and

Element Light 4-7
4413 12-Hour Timer and Cook Light 4-8
4414 Mini-Relay-Thermostat Interrupt 4-8
4415 Hold Light Thermostat and

Hold Light 4-8
4416 150°F Hold Temperature Control 4-9
4417 Contactor-Hold Heat and

Fan Control 4-9
SECTION 5 ILLUSTRATED PARTS LIST
51 General 5-1
52 Ordering Information 5-1
53 Index of Illustrated Parts List 5-1

Page

LIST OF ILLUSTRATIONS

Figure

SECTION 2 OPERATION

2-1 Controls & Indicators

3-1 Pictorial Schematic- Typical Configuration 3-2
SECTION 4 TROUBLE-SHOOTING
4-1 Wiring Diagram-208/240 Volt, Single & 3 Phase,

60 Hz

4-2 Wiring Diagram - 440/480 Volt, 3 Phase, 60 HZ
4-3 Wiring Diagram - 220/380, 240/415 Volt 3-Phase

50 HZ, 4-Wire

Page

2-2

4-10

4-11
4-12

LIST OF TABLES

SECTION 2 OPERATION

2-1 Controls & Indicators 2-3

Figure

4-4 Schematic Diagram - 208/240 Volt, 3-Phase,

60 HZ

4-5 Schematic Diagram - 220/240 Volt, Single

Phase, 60 HZ

4-6 Schematic Diagram - 440/480 Volt, 3-Phase,

60 HZ

4-7 Schematic Diagram - 220/380, 240/415 Volt, 3

Phase, 50 HZ

SECTION 5 ILLUSTRATED PARTS LIST

5-1 Control Panel Assembly 5-2
5-2 Electrical Control Assembly 5-4

SECTION 4 TROUBLE-SHOOTING

4-1 Trouble-Shooting Guide

4-2 Major Electrical Fault Isolation Guide

Page
4-13

4-14

4-15

4-16

4-1
4-4

SECTION 1 INTRODUCTION

1-1

17-0406

This service and parts supplement to Power Saver II Electric Convection Oven Service & Parts Manual

contains descriptive information, trouble-shooting and maintenance information, and parts identification for

ovens equipped with Cook & Hold controls. Only information pertinent to these controls is contained in the

supplement. For details of standard oven controls and all other assemblies, see

Service & Parts Manual

1.1 DESCRIPTION
The Model 2400HE Power Saver II Electric

Convection Oven has Cook & Hold controls in addition
to the standard controls of the Model 2800HE Power
Saver II Oven. A selector switch allows the operator to
use either standard (COOK) oven operation or COOK
& HOLD operation. Controls and circuits spec ific to
COOK & HOLD ovens are included in this supplement.

1.2 BASIC FUNCTIONING

Operation of the oven in the Cook & Hold mode is
preceeded by preheating. Preheating is done by
placing the selector switch in the COOK (up) position,
power switch ON and thermostat set at 350°F. for 15
minutes operation.

Initial Roasting - The oven is then loaded, the
selector switch placed in the COOK & HOLD (down)
position, the thermostat set to the required roasting
temperature and the 12-hour timer set for the
approximate roasting time. (Times vary from normal
roasting and are supplied by Market Forge in
Operator's Manual 17-0405). The convector fan will
operate and the COOK light will come on indicating
contactors have closed to heating element circuits and
roasting cycle has begun under control of the
thermostat.

Residual Heat Roasting - When the 12-hour timer
setting has elapsed and the dial has returned to the "0­minute" position, the thermostat and fan circuits are
interrupted to stop fan and heating element operation.
During this cycle only stored heat is used for cooking,
which continues until the oven temperature drops to 1
50°F.

17-0393.

Hold - When the temperature sensor located at the
rear of the oven interior registers a temperature drop
to 150°F., it activates a temperat ure control device to
maintain the 150°F. temperature for an indefinite
period. The control functions through a separate
contactor to control a single heating element and the
convector fan simultaneously. The control cycles the
heater and fan on and off in response to demand of
the sensor. A separate Hold light thermostat closes at
150°F. to verify the Hold cycle by lighting the HOLD
indicator light. The oven remains in the Hold condition
until the 12-hour timer is turned to the OFF position.

All other oven operation, including the Cook mode
is described in the service and parts manual for the
Power Saver II Convection Oven.

1.3 SERVICE

Should repairs be required, a network of authorized
service agencies is available to assist with prompt
service. A current Director of Authorized Service
Agencies and service assistance may be obtained by
contacting:

Product Service Department
Market Forge
35 Garvey Street
Everett, Massachusetts 02149
Tel.: [phone]

Product Service Department
Market Forge Canada Ltd.
1375 Aimco Boulevard, Unit 5
Mississauga, Ontario,
Canada L4W 1 B5

Tel.: [phone]
The model and serial numbers must be referenced
when corresponding with Market Forge.

SECTION 2 OPERATION

2.1. OPERATING CONTROLS AND

INDICATORS

All controls required to operate the Power
Saver II with Cook & Hold are listed in Table 2-1
with a short functional description of each. Figure
2-1 shows the physical location of each control
and indicator.

2.2 OPERATING PROCEDURES

The Cook & Hold oven may be used as either a
standard oven or an oven which roasts and then
automatically holds at 150°F. for an indefinite
period. Instructions for operation in either cooking
mode are included in this section.

2.2.1 Preheating

1. Arrange shelf positions according to the food
product to be cooked. Refer to Test Kitchen
Bulletin #41 for correct positioning.

2. Place selector switch in the COOK (up) position
and close doors.

3. Place power switch in the ON position. Fan will
begin rotating.

4. Set thermostat dial to desired cooking
temperature. ELEMENTS indicator light will
come on.

5. Allow oven to preheat for about 15 minutes.
Preheating is complete when ELEMENTS
indicator light goes out.

2.2.2 Cook Mode Operation
The oven is ready for cooking use when the

ELEMENTS indicator light goes out following
preheating, (See subsection 2.2.1). For standard
cooking proceed as follows:

1. Load food into oven and close doors.

2. Set 60 MINUTE timer for desired cooking time.
Buzzer will sound at end of preset interval. For
cooking times longer than 60 minutes, reset
timer for additional time. (Timer is a
convenience feature only and has no oven
controlling function).

3. Unload oven and proceed as follows:
a. If oven is to be turned off, place thermostat dial

and power switch in OFF position.

b. If oven temperature is to be reduced, reset

thermostat to the desired temperature and
close the right door. Fan will continue to
operate with left door open. When ELEMENTS
indicator light comes on, oven is at lower
temperature. Left door is then closed until light
comes on to show that temperature has
stabilized.

4. Leave doors ajar if shut -down is to be longer than
one day.

2.2.3 Cook & Hold Operation
The oven is ready for cooking use when the

ELEMENTS indicator light goes out following
preheating, (See subsection 2.2.1). For Cook &
Hold operation proceed as follows:

1. Load food into oven and close doors.

2. Place selector switch in COOK & HOLD (down)
position.

3. Reset thermostat dial to initial roasting
temperature. (See Operators Manual, #17-0405 for
recommended temperature settings).

4. Set 12-HOUR timer (5-Hour Timer on some early
units) to approximate roasting time. (See
Operator's Manual #17-0405 for recommended
time settings). COOK indicator light will come on
and stay on throughout Cook & Hold operation.

NOTE
Once controls are set, all operation is automatic
and continuous. At end of primary cooking cycle,
when 12-HOUR timer dial has returned to '0­minute' position, fan and heaters will shut off.
Product continues to cook with stored heat. 12­HOUR timer must be left at '0-minute' position for
automatic operation to continue.

2-1 17-0406

2-2 COOK & HOLD POWER SAVER

CAUTION

Do not open doors or return timer dial to OFF
position until ready for oven unloading. If doors
are accidentally opened product must be finished
in Cook mode with meat thermometer used to
test doneness.

5. Unload the oven at any time after the HOLD light
comes on.

NOTE

HOLD light comes on when oven temperature
drops to 150°F. to indicate cooking is completed
and product is on hold for unloading as needed.
Heat and fan will operate intermittently as needed
to maintain 150°F.

6. Return 12-HOUR timer to OFF position when all
product has been removed from the oven.

7. Place thermostat dial and power switch in OFF
positions and leave doors ajar for daily shut down.

17-0406

Figure 2-1. Controls and Indicators

OPERATION 2-3

OPERATING CONTROLS AND INDICATORS

Controls electrical power to control circuits and convector fan motor. Must

Hold mode.

f with

out all phases of

Hold mode and will

TABLE 2-1

FIGURE 2-1 REF. DESCRIPTION FUNCTION

1 Circuit Breaker

2 Power Switch

3

4

Cook/Cook & Hold Selector
Switch

Thermostat Control

5 Element Indicator Light

6 60-Minute Timer

7 12-Hour Timer

8 Cook Indicator Light

Protects control circuits and conv ector fan motor. Must be in ON position
for oven to operate.

be in ON position for oven to operate.
Selects standard (Cook mode) baking and roasting or Cook &

Regulates oven temperature. Controls heating element operation.
Indicates when lit that thermostat is calling for heat. Cycles on and of

thermostat control.
Electric timer to aid operator in timing Cook mode operation. Does not

control oven operation. Sounds buzzer at end of timed interval. Place in
OFF position to silence buzzer.
Controls duration of primary roast cycle in Cook & Hold mode. When
preset time has elapsed, timer is left at '0-hour' position until stored heat
cooking is completed. Product is cooked and can be held or used as
desired when HOLD light comes on. Timer setting is changed from '0­minute' to OFF only when oven is unloaded.
Indicates when lit that 12-HOUR timer has been set, and that selector
switch is in COOK & HOLD position. Remains on through­Cook & Hold operation.

9 Hold Indicator Light

Indicates when lit that oven is in Hold phase of Cook &
maintain 150°F. 65°C. until 12-Hour timer is manually shut off.

17-0406

SECTION 3 PRINCIPLES OF OPERATION

3.1 GENERAL

The model 2400 HE Electric Convection Ovens are
equipped with an optional factory installed control
system which povides operator selection of standard
(Cook) operation or Cook & Hold operation. The oven
is otherwise constructed like model 2800 HE Power
Saver II. Principles of operation for the oven as a
whole are included in section 4 of service and parts
manuals #17-0393. The following description of
functions and controls is for Cook & Hold models only.

3.2 THEORY OF OPERATION

Cook & Hold controls include power circuits and
control circuits for operation of the oven in two modes.
A brief description of the sequence of events and
interdependence of components in each mode follows.
Simplified Schematic figure 3-1 shows the
interrelationship of each component described below.

3.2.1 Power and Heating Element Operation

Incoming power is supplied to the oven from a
terminal block at the lower, front right side of the oven.
Power is connected from the terminal block to three
contactors which control operation of heating
elements. (A fourth contactor in 440/480 volt units is
used for the fan motor). A single phase branch circuit
from the terminal block connects to the control panel
circuit breaker. (In 440/480 volt ovens, a step-down
transformer is included before the circuit breaker to
supply 220 to 240 volts).

When the control circuit thermostat requires heat in
either the Cook mode or the 'Cook' cycle of the Cook
& Hold mode of operation, two contactors are
energized to power the five heating elements inside
the oven. When satisfied, the thermostat opens the
coil circuit to break power to the heaters. On-off
operation proceeds throughout oven operation.

A third identical contactor controls the power circuit
to a single 2600 watt heating element during the 'Hold'
cycle of Cook & Hold operation. It opens and closes
under the control of a 150°F. temperature control
device. Only two sets of contacts are required for
heater control. The third is used for simultaneous on­off control of the fan motor.

3.2.2 Cook Mode Controls

With the control panel circuit breaker in the ON
position 208 to 220 volt service is connected to the
power switch. The power switch is the routine on-off
control for the oven. A normally open switch actuated
by closing the right side oven door functions as a
circuit interrupter to prevent operation unless the door
is closed. Power is brought up to the control
components when the power switch is in the ON
position and the right side door is closed.

A double-pole, double-throw selector switch which
functions as the mode selector switch is placed in the
COOK (up) position. The convector fan begins to
operate immediately, remaining on continuously
during Cook mode operation. The 475°F. (maximum
setting) thermostatic control is set to the required
preheat or baking temperature. Setting the dial when
the oven is cold automatically closes the thermostat
contacts to light the ELEMENTS indicator light and
energize the two contactor coils controlling the heating
elements. Thermostat contacts remain closed until the
capillary bulb inside the oven senses sufficient
temperature rise to open them. Elements are cycled
on and off by the thermostat as needed to maintain
temperature setting.

A 60-minute electric timer included as an operator
convenience has no controlling function. The dial is
set to the required oven operating time. At the end of
the timer setting a buzzer sounds until the dial is
returned to the OFF position.

3-1

3-2 COOK & HOLD POWER SAVER II

Figure 3-1. Pictorial Schematic — Typical Configuration

3.2.3 Cook & Hold Mode Operation
The same control circuit components are utilized

for Cook & Hold operation as for the Cook mode
except for the 60-minute timer. Setting the selector
switch in the COOK & HOLD (down) position supplies
power to control components for that mode. In normal
use the oven is first preheated in the Cook mode as
described in 3.2.2. The thermostat is then set to the
required initial roasting temperature prior to switching
to Cook & Hold.

Immediately on setting the selector switch to
COOK & HOLD, the COOK indicator light turns on.
The 12-hour timer, used for this mode, is set for the
initial roasting time. Timer contacts close to the fan
motor circuit to begin operation.

17-0406

Another circuit is closed to energize the coil of a
normally open single-pole relay (C4) which in turn
completes the circuit between the thermostatic control
and the heater contactor coils. Controls operate in
these positions, with timer motor running under the
continuous on-off control of the thermostat.

When the 12-hour timer setting elapses, the
common element transfers to complete a circuit to
'Hold' cycle components. Simultaneously the timer
motor and convector fan motor circuits are opened.
The relay contacts between the thermostat control and
heater element contactors are opened to interrupt
control by the thermostat. The oven is now in residual
heat roasting with only the COOK indicator light on.
The residual cycle continues until, by normal oven
heat loss, the interior temperature drops to 150°F.

PRINCIPLES OF OPERATION 3-3

The 'Hold' cycle of Cook & Hold operation is
controlled by a solid state 150°F. temperature
control. A thermistor probe mounted inside the oven
activates the control when the temperature drops to
150°F. Control contacts close to complete a circuit
to the contactor coil for single heater and fan
operation in the 'Hold' cycle. Each time the 150°F.
control contacts close the contactor pulls in to
power one 2600 watt heating element and the
convector fan. On-off operation proceeds
throughout the 'Hold' cycle, varying approximately +
1°F.from 150°F.

Simultaneous with 150°F. control operation, a
separate (normally closed at room temperature),
thermostat for the HOLD light senses interior oven
temperature. On temperature drop to 150°F. its
contacts close to turn on the HOLD light. Unlike the
150°F. control device, the light thermostat operates
in a wide temperature range from 150°F. to 170°F.
It keeps the HOLD light on throughout the 'Hold'
cycle, while the oven temperature fluctuates above
and below 150°F.

The 150°F. temperature control and HOLD light
thermostat operate throughout the 'Hold' cycle until
interrupted. Placing the 12-hour timer dial in the
OFF position terminates operation of both
thermostatic controls.

3.3 ELECTRICAL CIRCUITS

The electrical circuits for Cook & Hold controls
consist of the 208/220 or 440/480 volt power circuits
and the 208/220 volt control circuits. They contain
all contactors, relays, switches, timers, indicator
lights and wiring required for oven operat ion.

3.3.1 Power Circuit Components

The power circuits are shown in wiring diagrams
and schematic diagrams, figures 4-1 through 4-7.
Line voltage is connected to the line terminals of
two 30 Amp. contactors. Contactor load terminals
are connected to the leads of two 1300 watt and
three 2600 watt heating elements mounted inside
the oven. A third 30 Amp. contactor is connected to
two input poles with output to one 2600 watt
element for use in the 'Hold' cycle only. A fourth 10
Amp. contactor is used for fan motor control in
440/480 volt units only. All power circuit controls are
activated by the control circuits.

3.3.2 Control Circuit Components
Control circuits are shown in wiring diagrams and

schematic diagrams figures 4-1 through 4-7. Control
circuits are powered from a branch line off L3 and one
other terminal block terminal depending on voltage
characteristics for the oven. Input controls have
common use for both Cook and Cook & Hold modes
up to the selector switch. Beyond the mode selector
switch many controls are used for one mode only.
Components for each mode are described in the
following paragraphs.

3.3.2.1 Control Circuit Components For Both

Modes.

The components which control power to both Cook

and Cook & Hold controls include the following:

1. Tr ansformer - (440/480 volt ovens) -A 440/480 volt
to 220/240 volt step-down transformer supplies
input power for the control circuit. The primary field
windings are connected to L2 and L3 terminal
block locations.

2. Circuit Breaker - 15 Amp., 2-pole circuit breaker
provides overload protection for the control circuit.
Normally left in the ON position, it supplies 208 to
220 volts to the power switch.

3. Power ON-OFF Switch - A double-pole, double­throw toggle switch provides routine on-off control
for the oven. In the ON position it connects
through one pole to the door switch, and through
the second pole to the L3 power feed for all
components.

4. Door Switch - A single-pole, normally open, micro­switch actuated by closing the right side oven
door. It serve s as a circuit interrupter, stopping all
oven operation unless the door is closed. When
closed it completes the circuit from one selector
switch common element to the 475°F. operating
thermostat contacts.

5. Thermostat Control - A maximum setting 475°F.
control for oven operating temperature. A capillary
bulb mounted inside the oven is permanently
connected to the bellows in the control. When
thermostat contacts are closed a circuit is
completed to one common element of the selector
switch.

17-0406

3-4 COOK & HOLD POWER SAVER II

6. Mode Selector Switch - A double-pole, double-throw
toggle switch for selection of Cook or Cook & Hold
operation. Power is supplied to the two common
elements through controls described above. Output
terminals are connec ted with appropriate
components for each mode.

3.3.2.2 Cook Mode Components. The only
components used exclusively for Cook mode
operation are the 60-minute timer and buzzer. The
timer is a convenience item only and has no
controlling function. When the dial is set the common
element closes a circuit to the timer motor to maintain
timer operation. At the '0' minute setting the common
element switches to contacts for the buzzer circuit.
The buzzer sounds until the timer knob is placed in
the OFF position.

Other components used for the Cook mode are the
ELEMENTS indicator light and heater element
contactors which cycle on and off by control of the
475°F. thermostat control. The convector fan operates
continuously.

3.3.2.3 Cook & Hold Mode Components.
When the selector switch is placed in the COOK &

HOLD position the following components function to
control operation.

1 12-Hour Timer - The timer controls the duration of

initial roasting and switches to the 'Hold' cycle. The
common element is connected to one Cook & Hold
terminal of the mode selector switch. When set for
initial roasting, the timer completes a circuit to the
convector fan motor and timer motor, and closes a
relay in the thermostat circuit to the heater
contactors. At the end of the initial roasting period
the common element switches to the hold
component circuit. It remains in this position until
the dial is moved to the OFF position.

2. Relay C4-A single-pole, normally open relay.
Its coil is energized when the 12-hour timer is set
for initial roasting with closed contacts

ostat control to heater contactors. When the 12­hour timer reaches '0' hours, the relay coil circuit is
opened, in turn causing relay contacts to open so
that the 475°F. thermostat circuit to heater
contactor is interrupted.

3. COOK Light - The light (red lens) is connected to
one selector switch terminal for Cook & Hold
operation. It comes on immediately upon setting
the switch.

4. 150°F. Temperature Control - A solid state
temperature actuated switch device, with switch
contacts normally open at room temperature. It is
actuated by a thermistor probe mounted inside the
oven and connected electrically to the control.
Operating potential is connected from L3 on one
side, and the 'Hold' cycle terminal of the 12-hour
timer on the other. The control/probe system
functions to maintain 150°F. temperature during
the 'Hold' cycle. When the oven temperature drops
to 150°F. at the end of residual heat roasting, the
control contacts close a circuit to the coil of the
contactor for 'Hold' cycle heater and fan control.
The contactor opens and closes under the control
of the 150°F. control until the 12-hour timer dial is
returned to the OFF position.

5. HOLD Light Thermostat And HOLD Light - A
separate button type thermostatic switch, normally
closed at room temperature is used to control
HOLD light operation. Its contacts close on
temperature drop to 150°F. and open on rise to
170°F. It functions to keep the HOLD light on
continuously during the 'hold' cycle.

completing the circuit from the 475°F. therm-

17-0406