Thermostatic Control - Market Forge Industries 2500 HE Service & Parts Manual

5.4.4 Thermostatic Control

5.4.4.1 Thermostat Contacts
Defective contacts will result in failure of the
oven to operate properly. If the ignition system fails
to operate when the thermostat knob is set to the
desired temperature, the fault may be the
thermostat switch contacts or thermostat wiring.
When this occurs, remove the control panel
(subsection 6.4.1) and proceed as follows.
1. Turn off power to the oven at external (main)
circuit breaker
2. Disconnect all wires (8,9,18) from thermostat
terminals (See Figure 5-1)
3. Connect an ohmmeter between the terminals
4. Rotate the thermostat knob to the maximum
setting With the oven cool, a zero ohm reading
should be obtained on the ohmmeter. If zero
reading cannot be obtained, contacts are
defective and the thermostat must be replaced.
5. Remove ohmmeter and replace all leads on
terminals as shown in Figure 5-1
5.4.4.2 Thermostat Capillary
A defective or punctured capillary/bellows
system may cause continuous operation of the
burners. If continuous operation occurs and
recalibration of the thermostat as explained in
subsection 6.3.2 fails to correct the problem, the
entire thermostat control must be replaced
5.4.5 Solenoid Gas Valve
When the solenoid gas valve fails to operate,
the fault may be a defective valve or control board.
An a-c voltmeter is used to check the voltage at the
coil wire terminals with the oven operating.
If voltage of 120 volts is present, the valve is defective
and must be replaced as a unit If 120 volts is not
present and all wiring connections are tight, the
ignition control board is defective and must be
replaced
5.4.6 Wiring
All the electrical components of the HE oven (ON-
OFF switch, door switch, thermostat control, gas
solenoid valve, RESET switches, ignition control
board, and indicator light) are connected to each other
by wiring shown in Figure 5-1. If all of the electrical
components are operating correctly (and the incoming
power has been checked) but the unit fails to operate,
the fault lies in the wiring.
Figure 5-1 is a wiring diagram which shows all
terminals and interconnections within the electrical
circuits All numbered terminals are identified and all
leads number coded as shown Connections can be
easily removed Figure 4-2 shows the same
information schematically and is an aid in isolating
circuits for testing
Using an ohmmeter, wiring continuity between the
connections shown on the wiring diagram (Figure 5-1)
is readily verified. This is best done in stages,
removing only those wires required for each continuity
check. As each lead is replaced, it should be checked
for evidence of corrosion and cleaned if necessary. All
leads must be tightly attached to provide a good elec-
trical connection.
5.4.7 Buzzer Relay
A defective relay will cause continuous sounding
of the buzzer when the thermostat is set If the buzzer
is sounding but the burners are operating properly, the
relay is defective and must be replaced.
5-5 S2207