Repair manual
MT3855
5
CONVECTION SYSTEM
POSSIBLE CAUSE(S) SUGGESTED REMEDY
Symptom #1 - Blower motor(s) not running
Oven in OFF mode.
Emergency stop switch on OFF.
No power to oven.
Motor circuit breaker tripped.
Faulty start capacitor.
Motor(s) burnt out.
Motor contactor open.
Thermal overload tripped.
Press ON/OFF key.
Pull switch out to ON.
Verify power to motor(s). If there is voltage presĆ
ent, replace the motor. If voltage is not present,
check the motor contactor.
Replace fuse. Determine amp draw.
Replace capacitor.
Check draw (3amps or greater).
Check that the computer is turned on and that a
cook time and temperature have been proĆ
grammed. Check for voltage to the coil of the moĆ
tor contactor. If voltage is present, replace the
contactor. If voltage is not present, check that the
blower relay is closed. If not, check for voltage at
the blower relay coil. If a 12 VDC voltage is presĆ
ent at the coil the blower relay is bad. If there is
no voltage present at the coil the computer may
need to be replaced.
Determine if the cooling blower (or fans) are operĆ
ating. If not, verify voltage to the cooling blower.
If voltage is present, replace the cooling blower
motor. If voltage is not present, verify voltage
through the thermal switch. If no voltage is presĆ
ent, replace the thermal switch.
Symptom #2 - Blower motor(s) do not shut off
Faulty motor contactor.
Faulty blower motor relay.
Faulty auxiliary contact.
Faulty probe.
Faulty computer.
Replace contactor.
If the temperature probe is good check for voltĆ
age at the coil of the blower relay. If voltage is not
present the relay is bad. Replace the blower
relay.
Replace auxiliary contactor.
Check the resistance values of the temperature
probe for values from 135Ć170F (57Ć77C). RefĆ
erence TABLE 6 on page 6-10 of the Technical
Appendix. If the values do not agree with the
chart change the probe.
If voltage is present at the blower relay, the comĆ
puter is bad. Replace the computer.