I have a Kitchenaid KSRA25FKSS00 where the over temperature keeps on getting triggered. About 18 months ago, i had a similar issue. I blow dried all the freezer coils and that addressed the issue until now. The issue started happening last week. The fridge did get warmer and I noticed some slight frost buildup on the diffuser and the fridge was warmer. So I blow dried all the freezer coils (and diffuser) and that seemed to have fixed the issue for 4-5 days, but it started happening again today. What is happening now is the over temperature indicator is going off every 90 minutes. I do feel some cold air coming out of the diffuser. There is a bit of frost buildup on the diffuser. The return air area at the bottom is free of any frost. If I open the fridge and put my hands on the diffuser there is some cold air coming out. However if I then open the freezer door at the same time, a lot more cold air immediately comes out of the diffuser. Any ideas on what it can be?

I just defrosted the coils for a second time and prior to defrosting I took pictures of the coils. Seems to be over frosted? See links below for images
http://thebizservices.ne...idge/20180311_224014.jpg
http://thebizservices.ne...idge/20180311_224414.jpg
http://thebizservices.ne...idge/20180311_224438.jpg
http://thebizservices.ne...idge/20180311_224529.jpg

Could it be the defrost thermostat:
Whirlpool WPW10225581 Defrost Thermostat - AppliancePartsPros.com

Any other possibilities?

Thanks!