Market Forge ST-10M24D Service Manual
ST-10M SERIES
10 PAN CONVECTION STEAMERS
PARTS AND SERVICE MANUAL
EFFECTIVE AUGUST 12, 2014
The Company reserves the right to make substitution in the event that items specied are not available.
ERRORS: Descriptive and/or typographic errors are subject to correction.
44 Lakeside Avenue, Burlington, Vermont 05401 USA Telephone: (802) 658-6600 Fax: (802) 860-3732
Superseding All Previous Parts Lists.
MARKET FORGE INDUSTRIES
www.mi.com
P/N 14-0288 Rev A (8/14)
TABLE OF CONTENTS
PRINCIPLES OF OPERATION ..........................................................3
TROUBLESHOOTING ..................................................................5
WIRING DIAGRAMS & SCHEMATICS ...................................................9
REPAIR AND REPLACEMENT ........................................................ 13
ILLUSTRATED PART LIST
DOOR ASSEMBLY ................................................................... 15
CABINET ASSEMBLY ................................................................ 16
CONTROL PANEL ASSEMBLY ........................................................ 18
CONDENSER ASSEMBLY ............................................................ 19
COMPLETE CONDENSER ASSEMBLY ................................................ 20
POWER PLUS ....................................................................... 21
AUGUST 12, 2014 2 ST-10M SERIES CONVECTION STEAMERS
PRINCIPLES OF OPERATION
GENERAL
The ST-10 Pressureless Steam Cooker consists of two
identical cooking compartments, one above the other, in
a single cabinet assembly. Each compartment is tted
with independent electrically controlled steam circuits and
spring-loaded, self-sealing doors with slam action latches.
Compartments can be used separately or simultaneously
for either constant steam or 60-minute timing. The principles of operation in this section include an explanation
of steam, steam condensing, and electrical circuits and
their functioning.
PLUMBING CIRCUITS
The plumbing circuits consist of the piping, steam solenoid valves, orice, drain, and cold water condenser required to provide controlled steam application to the cook-
ing compartments. A simplied diagram of these circuits
is shown below.
Steam inlet lines for compartments are equipped with
normally closed solenoid valves operated by the electrical control circuits. The inlet valves are opened whenever
the compartment control circuit is activated by use of the
60-minute timers.
STEAM INLET LINE
A steam supply line is plumbed from the boiler output (or
direct-connected steam control) to a 1/2-inch barb tting
connected to the input sides of both steam inlet solenoid
valves. When a cooking compartment is not in use, the
valve for the compartment remains closed to prevent
steam from entering. During operation, the appropriate
inlet solenoid valve is opened by activation of the control circuit. Steam is projected onto the surface of pans
of food loaded into the compartment by an orice located
inside the compartment. Steam continues to ow through
the compartment in this manner until the control circuit
closes the solenoid valve.
STEAM EXHAUST AND DRAIN LINES
Perforated strainers at the drain line openings inside each
compartment allow only steam, condensation, and liquid
cooking drainage to enter. Prior to discharge into the boiler drain system, steam is converted to water by the cold
water condensing systems for each compartment.
Figure 1
NOTE: This is strictly a pictorial schematic diagram and
is not intended to show the actual conguration of
the plumbing. All components are shown in correct relationship with each other. However, the
diagram does not show their actual locations or
position within the cooker.
As shown in the diagram, steam inlet and exhaust connections are connected at the factory directly into a steam
boiler or direct-connected steam plumbing enclosed
within the base cabinet on which the cooker is mounted.
The boiler (or direct-connected steam control system) is
equipped to supply constant, regulated steam at 14–15
PSI. Steam exhaust, having been reduced to water by the
cold water condenser, is directed into the boiler (or direct-
connected steam control) drain system.
STEAM EXHAUST CONDENSING SYSTEM
The steam condensing system consists of the identical,
two-position, normally closed cold water solenoid valves,
with outlet sides connected into the exhaust plumbing for
each cooking compartment. A spray nozzle directs cold
water about the inside of the drain lines to increase cold
water contact with exhausted steam. Valve inlet sides
are connected remote from the supply line of the steam
boiler (or direct-connected steam plumbing). The valves
respond to a thermostatic switch located inside the compartment. When the timer starts the cold water solenoids
will energize.
ELECTRICAL CIRCUITS
The electrical circuits of the cooker control the power to
activate timer motors and energize solenoid-operated
valves and circuits, which in turn control application of
steam to the cooking compartment and condensation
of steam from the exhaust line. The cooker operates on
120V, 2 amp, 60Hz electrical service connected to all circuits from the circuits of the steam boiler (or direct-con-
nected steam controls) contained within the cabinet on
which the cooker is mounted. Power is supplied to the
control circuit at all times when the shut-off device for the
unit (supplied by the user) is in the ON position.
PRINCIPLES OF OPERATION
CONTROL CIRCUIT COMPONENTS
A brief description of the electrical circuit elements follows.
60 Minute Timer/Constant Steam
The timer contains a 120-volt AC synchronous motor that
drives a timing dial through a gear reduction and clutch
mechanism. The timer dial is manually set for any interval
of operation from 0 to 60 minutes or constant steam as
read on the calibrated dial face. The manual rotation of
the dial moves the common element (1) of the timer switch
from the neutral (OFF) position to contact (3), which connects with the steam inlet solenoid valve operating circuit.
The cooker is placed into automatic operation with the
setting of the timer dial. Its timing cycle, however, is automatically delayed by a thermostatic switch, which assures
operating temperature is achieved before the timer motor
begins to “time out.” When the timer motor has operated
for the preset duration, the common element is transferred to contact (4), returning the inlet solenoid valve to
the closed position and energizing the buzzer. Contact to
the buzzer circuit remains closed until the dial is manually turned to the OFF position, returning the common element (1) of the timer switch to the neutral position.
DOOR INTERLOCK SWITCH
The interlock switch is a single-pole proximity switch with
normally open contacts. The switch is operated by the
proximity of a magnet within the door. When the door is
open, the switch contacts remain in the open position.
When the door is closed and securely latched in place,
the magnet is near the switch to close the contacts. Connected between the operating contact (3) of the timers
and the steam inlet solenoid valve, the door switch acts
as a protective device to interrupt valve operation unless
the door is closed.
THERMOSTATIC SWITCH
The thermostatically operated switch is a two-position,
normally open switch mounted on the cooking compartment. The switch functions to activate the cold water solenoid valves of the steam condensing system and to delay
timer motor operation until the compartment temperature
reaches 195°F, thus assuring that cooking temperature
exists throughout the timed duration.
INDICATOR LIGHTS
An indicator light is included for both compartments. The
light remains on (red) at all times when the coinciding timer dial is set and the door interlock switch is closed. The
light turns off at the end of the timed cooking duration.
BUZZER
The buzzer is an alarm device that operates by oscillation
of a striker against the core of an electromagnet. When
the 60-minute timer dials reach the “0-Minute” position,
the buzzer coil is energized to sound the buzzer. Movement of the timer dial to the OFF position opens the contact to the buzzer coil to shut it off.
TROUBLESHOOTING
ELECTRICAL FAULT ISOLATION
Correction of an electrical failure rst requires isolation of
the fault to a single circuit or component. In most cases,
the nature of the failure and its effect upon the operation
of the cooker will be sufcient to narrow it down to one or
more circuit elements.
ELECTRICAL TROUBLE-SHOOTING PROCEDURES
Before performing the trouble-shooting procedures in this
section, the serviceman must be familiar with the function
of all controls as well as with the Principles of Operation
described the Operation Section.
GENERAL TROUBLE-SHOOTING GUIDE
PROBLEM PROBABLE CAUSE REMEDY
Indicator light fails to light with timer
set.
1. Power to cooker off.
2. Door interlock switch contacts
not closed.
3. Door interlock switch faulty.
4. Indicator light burned out.
5. Faulty timer contacts.
The electrical trouble-shooting procedures that follow require access to components and terminals of the electrical control panel. Electrical controls are reached by removing screws that fasten the control panel to the frame.
The panel may be pulled forward for testing while interconnected to the cooker circuits or disconnected at the
pin connection for complete removal and repair.
1. Locate external circuit breaker for incoming power and place in ON position.
2. Shut cooker door to close switch contacts.
Check alignment of door with switch.
3. Replace switch.
4. Replace light.
Steam fails to enter cooking compartment with indicator light on.
Steam enters compartment continuously. Timer dial not turning.
Steam continues to ow into compartment and/or buzzer fails to
sound at end of timer cycle.
Steam ows continuously from
boiler (or direct connected steam
control) drain line with cooker in operation.
6. Faulty wiring.
1. Faulty steam solenoid valve.
2. Faulty wiring.
1. Constant steam position.
2. Faulty thermostatic switch.
3. Faulty timer motor.
4. Faulty steam solenoid valve.
5. Faulty wiring.
1. Timer contacts faulty.
2. Buzzer faulty.
3. Faulty wiring.
1. Cold water not connected.
2. Faulty thermostat.
3. Faulty cold water solenoid.
4. Faulty wiring.
1. Replace valve.
2. Inspect condition of wire and tightness of
all connections. Correct as needed.
1. Move knob to timing location.
2. Replace switch.
3. Replace Timer.
4. Replace valve.
5. Inspect condition of wire and tightness of
all connections. Correct as needed.
1. Replace timer.
2. Replace buzzer.
3. Inspect condition of wire and tightness of
all connections. Correct as needed.
1. Turn on external shut-off valve.
2. Replace thermostat. Replace valve.
3. Inspect condition of wire and tightness of
all connections. Correct as needed.
TROUBLESHOOTING
Incoming Power
Before trouble-shooting any of the electrical parts or assemblies, verify that power is being supplied to the cooker. Incoming power is connected at the boiler (or direct-
connected steam) control box located in the base cabinet.
With power connected to the cooker, an AC volt-meter is
used to measure 120 volts across L1 and L2. If 120 volts
is present, and the cooker will not operate, the fault lies
within the electrical circuits of the cooker.
Electrical Inspection
The rst step in any electrical trouble-shooting procedure
is a thorough physical inspection of all wiring connections.
To access electrical components, remove the control panel.
ELECTRICAL FAULT ISOLATION GUIDE
FAILURE FAULT LOCATION
Will not operate in either CONSTANT STEAM or 60-MINUTE TIMER position. 1. Incoming power.
WARNING
Before removing control panel or checking
connections and wiring, be sure that the circuit breaker for incoming power is OFF. When
power is supplied, all exposed terminals of the
control panel carry 120 volts.
Check all wiring connections by hand to assure that both
ends of all connection points are tightly secured. Use a
screwdriver to tighten connection points. If necessary, visually inspect all quick-disconnect terminals for evidence
of corrosion. Terminals in this condition should be separated, cleaned with emery cloth until shiny, and tightly reconnected.
2. Timer.
3. Door interlock switch.
4. Wiring.
Operating in CONSTANT STEAM position but not in 60-MINUTE TIMER position.
Operating in 60-MINUTE TIMER position but not in CONSTANT STEAM position.
Steam solenoid valve fails to open with indicator light on. 1. Solenoid valve coil.
Indicator light OFF with steam solenoid open. 1. Indicator light.
With indicator light ON and steam solenoid valve OPEN, timer dial fails to
turn.
Buzzer fails to SOUND at end of 60-MINUTE TIMER mode. 1. 60-Minute timer.
Steam ows continuously from boiler drain line. 1. Thermostatic switch.
1. 60-Minute timer.
2. Wiring.
1. 60-Minute timer.
2. Wiring.
2. Wiring.
2. Wiring.
1. Compartment thermostatic switch.
2. Constant steam position.
3. Timer motor.
4. Wiring.
2. Buzzer.
3. Wiring.
2. Cold water solenoid valve.
3. Wiring.
TROUBLESHOOTING
60 MINUTE TIMER
Timer Contacts
Defective timer contacts will result in failure of either cooker compartment to operate. When this occurs, remove the
control panel, and proceed as follows:
4. Turn off power to the cooker at external circuit breaker.
5. Disconnect all ve wires from timer terminals.
6. Connect an ohmmeter between terminals 1 and 3.
7. Rotate timer dial beyond the “0-Minute” point (any
setting) to obtain a reading of zero ohms on the
ohmmeter. If zero ohm reading cannot be obtained,
timer contacts are defective and the timer must be
replaced.
8. Move ohmmeter leads to terminals 1 and 4.
9. Rotate timer dial to “0-Minute” position (an audible
click indicates correct position). If zero ohm reading
cannot be obtained, the timer is defective and must
be replaced.
10. Remove ohmmeter and replace all ve leads on timer
terminals.
Timer Motor
A defective timer motor will cause continuous operation in
the TIME mode, with the timer dial failing to return to the
“0-Minute” position. Since thermostatic switch failure can
cause the same symptom, fault must rst be isolated to
the timer by testing the thermostat.
To conrm timer motor condition, proceed as follows:
1. Carefully check motor wire leads and tighten loose
connections.
WARNING
Use care while working with control panel.
Terminals carry 120 volts.
2. Turn on power to the cooker.
3. Set timer dial (any setting beyond “0-Minute”). If operation is correct, the motor will turn the dial toward
“0-Minute.” If the motor fails to operate, it is defective
and the entire timer must be replaced.
DOOR INTERLOCK SWITCH
Malfunction of the cooker door interlock switch prevents
timer indicator lights from turning on and steam solenoid
from opening when the timer dial is set. If steam does not
enter the compartment and the indicator light fails to turn
on with the door latch securely engaged, the fault may be
in the door interlock switch.
Proceed as follows:
1. Turn off power to the cooker.
2. Disconnect wires to the door switch terminals
3. Connect an ohmmeter between the terminals of the
switch.
4. Actuate the switch by closing the cooking compartment door. If a zero reading cannot be obtained, the
switch is defective and must be replaced.
5. Remove the ohmmeter and replace the leads on
switch terminals.
STEAM SOLENOID VALVES
When either inlet solenoid valve fails to operate, the fault
may be a defective coil. A defective coil is found using an
AC volt-meter to check the voltage at the coil wire terminals, with the cooker compartment operating in either
CONSTANT STEAM or 60-MINUTE TIMER mode. If voltage of 120 volts is present and the coil fails to open the
valves, the fault is in the valve coil. Defective valve coils
are not separately replaceable, requiring complete valve
replacement.
INDICATOR LIGHTS
If the cooker compartment functions correctly, with the
single exception that the indicator light fails to light during
operation, the fault is a defective indicator light. A “burned
out” or defective light is veried by using an AC volt-meter
at the leads, with input power on the selector switch in the
correct position for that timer, the timer set, and the door
latches closed. If 120 volts is present, the fault is in the
indicator light and requires replacement. If 120 volts is not
present, the fault is in the wiring or control components
(selector switch, timer, or door switch).
4. Shut off power to the cooker.
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