see this causes and fix it. God bless you All microwaves have
some sort of a cooling fan to help keep the magnetron and controls at a
tolerable level. Most OTR models will usually use the vent motor for
the cooling fan also. Countertop units have a small fan behind the
control panel somewhere. Either way, if the cooling fan is not working
and heat builds up, it is going to open a thermostat. On some makes,
this thermostat might re-set itself as soon as the temperature cools
down. Other makes, you will have to replace the thermostat or fuse.If
this is your microwave oven repair problem, you will need to check the
operation of the fan. Below in the component testing chart, you will
see how to test the fan. Also, if possible, make sure the fan is not
obstructed somehow and not turning. Also check your fan relay at your
control board for voltage, if no voltage, replace control board. This
fan should come on at the same time any cooking starts.