Vulcan-Hart 126743, Service Manual

Page: 20 / 60

FULL SIZE ELECTRIC CONVECTION OVENS - SERVICE PROCEDURES AND ADJUSTMENTS
F25105 (December 2001) Page 20 of 60
TEMPERATURE PROBE TEST
(SOLID STATE CONTROL)
WARNING: DISCONNECT THE ELECTRICAL
POWER TO THE MACHINE AT THE MAIN
CIRCUIT BOX. PLACE A TAG ON THE CIRCUIT
BOX INDICATING THE CIRCUIT IS BEING
SERVICED.
NOTE: The temperature probe used in conjunction
with the Solid State Temperature control is an RTD
(resistance temperature detector) of the Thermistor
type. As temperature increases the resistance value
decreases.
1. Remove the right side panel as outlined under
"COVERS AND PANELS" in "REMOVAL AND
REPLACEMENT OF PARTS".
NOTE: If right side panel is not accessible, this
component can be serviced by removing the control
panel as outlined under "COVERS AND PANELS".
2. Place a shielded thermocouple in the geometric
center of the oven cavity and determine the
temperature in the oven cavity.
3. Remove the probe lead wires from the solid
state temperature control.
4. Test the probe with an ohmmeter.
A. If the measured resistance values are
inside the given tolerance then the probe
is functioning properly.
B. If the measured resistance values are
outside the given tolerance then replace
the probe and retest.
1) Check oven for proper operation.
5. Reverse procedure to install.
TEMP (°F) OHMS* TEMP (°F) OHMS*
77 90,000 360 822
240 4,077 380 656
260 3,016 400 529
280 2,266 425 424
300 1,726 450 334
320 1,332 475 266
340 1,041
(*) Resistance in ohms ± 10%
HEATING ELEMENT TEST
WARNING: THE FOLLOWING STEPS REQUIRE
POWER TO BE APPLIED TO THE UNIT DURING
THE TEST. USE EXTREME CAUTION AT ALL
TIMES.
1. Turn the power switch ON and set the oven
temperature control to the highest setting.
2. Measure the voltage at the heating element
terminals and verify it against the data plate
voltage.
A. If voltage is incorrect, find the source of
the problem.
B. If voltage is correct, check current draw
(amps) through the heating element lead
wires.
NOTE: This method is preferred over a
resistance check when a clamp on type amp
meter is available.
1) If current draw is correct then heating
element is functioning properly. See
table below for proper values.
2) If current draw is not correct, turn the
power switch OFF and disconnect
the electrical supply to the oven.
a. Replace heating element then
proceed to step 3.
C. If unable to check current draw, a
resistance check may indicate a
malfunctioning element.
1) Turn the power switch OFF and
disconnect the electrical supply to
the oven.
2) Remove the lead wires from the
heating element and check resistance
(ohms). See table below for proper
values.
3. Check for proper operation.
VOLTAGE
KW PER
ELEMENT
AMPS PER
ELEMENT
LEAD
OHMS PER
ELEMENT
1 PH 3 PH
208 2 60 35 21
240 2 52 33 28
480 2 15 4 111
NOTES: 1. Values in the table are nominal.
Tolerance is +5/-10%.
2. Voltage values are @ 60HZ.
3. Resistance values (ohms) are @
room temperature.