Maytag refrigerator does not defrost
 

My maytag (MSD2757AEB) refrigerator started having problems
a few weeks ago. It cannot defrost anymore. I've vacuumed and
manually defrosted it 2x since then. I've tried hitting the test and L1
on the controller but got a buzzing sound from the controller rather
than a single audible click (which is what I was expecting). I measure
about 25V across the thermostat when that happens. The thermostat
impedance seems ~250kOhms and the heater is not open. I am suspect
of the thermostat though with the 25V across it. At this point I am not
sure if it is the controller or the thermostat/heater (since they are sold
as a unit). But I have pretty much ruled out the fans, motors, seals,
compressor problem, etc. Any thoughts?

Thanks