Merco 86002 Kurzanleitung
MHCservmanual REV: B
PARTS AND SERVICE MANUAL
FOR
MERCO HOLDING CABINET
MODEL 86002
Merco Savory, Inc.
1111 North Hadley Road
Fort Wayne, Indiana 46804
United States of America
Phone: (260) 459-8200
U.S. Facsimile: (888) 790-8193
Int’l Facsimile: (260) 436-0735
Service Hotline: (800) 678-9511
www.mercosavory.com
Holding Cabinet – Service Manual
3
MHC-22-GEN CONTROL PANEL
MODEL 86002
Bin Button #2
Bin Button #1
Bin Button #4
Bin Button #3
Program Button
Time Button
Temperature Button
Down Arrow Button
Up Arrow Button
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4
WIRING DIAGRAM
Holding Cabinet – Service Manual
5
SEQUENCE OF OPERATION
Power Supply
Electrical power is supplied to the unit by a 3 conductor service for single
phase.
120VAC
Black conductor is hot.
White conductor is neutral.
Green and yellow conductor is ground.
Power is permanently supplied to the main power switch.
Heating Circuit
Closing the main power switch supplies voltage to the power board and user
interface.
Temperature is set through the user interface which then intermittently
supplies 120VAC to the heater plates. Temperature is then controlled by the
thermocouples sending a reference signal back to the user interface.
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6
TROUBLESHOOTING GUIDE
SYMPTOM POSSIBLE CAUSE EVALUATION
Holding Cabinet will
not heat
Incoming Power Supply Verify power cord is secured firmly in receptacle.
Measure the incoming voltage. Check circuit
breakers. Reset if required. Call power company
if needed.
Power Switch Check continuity between switch terminals.
Replace switch as needed.
Unit doesn’t reach
desired temperature
Thermocouple Check for continuity in circuit.
Heat Element Compare cavity temperature with display reading.
Insert temperature probe into center of cavity.
Acceptable temperature variation is +/- 20° from
display reading.
Check for loose connection.
Check the Amp draw on each element for proper
load. Check page 2 for rating information. If the
amp draw is high or low, check the individual
elements for opens, shorts and proper resistance.
WITH POWER OFF: To check resistance of the
elements, remove all leads from the elements and
use a digital multimeter.
The element resistance should be as follows:
120V – 87 ohms
Replace heating element (shelf) as needed.
Check thermostat (common wire). Please note
that if thermostat is bad, both circuits will be bad.
Temperature is too
high
Thermocouple Check for incorrectly wired thermocouple.
Thermocouple wire polarities are reversed.
Heat Element Compare cavity temperature with display reading.
Insert temperature probe into center of cavity.
Acceptable temperature variation is +/- 20° from
display reading.
Check for loose connection.
Check the Amp draw on each element for proper
load. Check page 2 for rating information. If the
amp draw is high or low, check the individual
elements for opens, shorts and proper resistance.
WITH POWER OFF: To check resistance of the
elements, remove all leads from the elements and
use a digital multimeter.
The element resistance should be as follows:
120V – 87 ohms
Replace heating element (shelf) as needed.
Holding Cabinet – Service Manual
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TROUBLESHOOTING GUIDE (CONT’D)
Display reads
unusual characters
Make sure wires are connected properly
(grounded).
If wires are grounded properly, new control board
is needed.
On/Off switch doesn’t
light (but unit works
properly)
Power Switch Check wiring to switch.
HEAT SHELF – REPLACEMENT
1. Disconnect power.
2. Take out screws holding “L Brackets” in cavity.
3. Disconnect thermocouple and all power connections to board. Mark all wires for reassembly.
4. Take out power board.
5. Take out shelf mounting screws from both sides.
6. Remove shelves and feed wiring out of unit.
7. Reassemble in reverse order.
USER INTERFACE (U.I.) BOARD – REPLACEMENT
1. Remove four (4) screws.
2. Disconnect thermocouples.
3. Disconnect ribbon cable.
4. Remove board.
5. Reassemble in reverse order.
WARNING:
Be careful to avoid tearing the aluminum foil while working with wire
connections.
!
!
When replacing U.I. board, be
sure ribbon cable is connected
so that blue wire is facing
towards interior of unit.
Holding Cabinet – Service Manual
8
PARTS BREAKDOWN
LABEL PART NUMBER PART DESCRIPTION
A 340040 Back Panel Assembly
B 340041 Side Panel
C 340042 Power Board Assembly
D 340043 Controller, User Interface
E 340038 Switch, Rocker, Lighted
F 10000949 Overlay, Control Panel
G 340045 Bracket, Heater Side
H 340046 Tray Seal
I 340011 Leg
J 340015 Tray, Plastic
K 340025 Tray Cover, Front Retention Rod, Assembly
L 10000968 Side Insulation
M 340048 Top / Bottom Insulation
N 10000966 Heater Insulation
O 10000946-02 Lower Shelf Assembly**
P 340051 Upper-Upper Shelf Assembly**
Q 340052 Lower-Upper Shelf Assembly**
R 340053 Rod, Rear Tray Seal Retainer
S 000171 Strain Relief
Not Shown 340054 Power Cord, NEMA 5-15P
Not Shown 340055 Ribbon Cable (Power Board to Interface)
Not Shown 340056 Cable (On / Off Switch to Power Board)
Not Shown 340017 Retention Rod Spring
Not Shown 340014 Retention Rod Spring Clip
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9
GENERAL VIEW
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10
DIAGNOSTIC MODE
►Press and hold down the “Temperature” button until you hear a short, double-beep sound.
In this mode all displays indicate temperatures for either the upper or lower heaters for
each bin. Pressing the “Up” and “Down” arrow buttons will select the upper and lower
heaters respectively.
In this mode, pressing the “Time” button will also display the PWM output power duty
cycle. This is shown as a percent for the corresponding heater.
The thermocouple calibration system can only be accessed from within the diagnostic
mode.
►THERMOCOUPLE CALIBRATION SYSTEM
Make sure heater zone to be calibrated is at temperature and stable. Measure actual
temperature and proceed with following procedure.
Enter “Diagnostic Mode” by pressing and holding down the “Temperature” button. After a
second or so, the actual temperatures as measured by holding cabinet are displayed.
Use “Up” or “Down” buttons to select either the upper or lower heating zone for each bin.
Press “Bin” select button to select bin containing heating zone to be calibrated.
Note: Bin display will alternate between showing temperature and calibration offset. As the
calibration offset is changed the temperature displayed will reflect this.
Use the “Up” and “Down” buttons to make the displayed temperature match the actual
temperature as independently measured.
To apply the temperature calibration correctly, press and hold the “Temperature” button
down. While pressing the “Temperature” button, press “Program” button (for 1 second)
until the unit beeps.
Once program in completed the temperature correction is applied and the heater zone will
adjust its temperature. The user interface returns to the actual temperature display.
Once a bin is selected for programming, if no keys are entered for 10 seconds the
calibration mode is terminated and the display returns to actual temperature display mode.
►THERMOCOUPLE FAULT DETECTION
The thermocouple (TC) fault detection logic is disabled for 10 minutes following initial
power application. This allows time for all heating zones to develop enough heat to not
trigger a shorted thermocouple fault.
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