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?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file
Upload is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.