The defrost t-stat that you used for a replacement should be OK, (2 degrees difference in opening temp isn't going to make any difference). The original 42-30F t-tstat close at 12 degrees, (just in case you may have thought the 30 was the closing temp, it's not - that is the differential temp). You replacement t-stat should be marked L44-26 if it really closes at 18 degrees as you note.
That small amount of difference wouldn't be causing it to run too much. You need to look at the frost pattern on the evaporator to make sure you have an even white frost coating from top to bottom and back to front of the complete evaporator - if the trailing section of the evaporator isn't frosting you could have the starting of a sealed system problem that would make it run lots longer and more often need it should.
Yes, I did think the second number was a shutoff temperature, so thanks for that clarification. According to the Amazon.com information for that part (#Part number: 4387503
), those are the correct operating numbers.
I will have to take the inner freezer panel off again to take a closer look at the pattern. By "trailing" do you mean the part of the evaporator closest to the draining hole?
If it's something unrelated to my recent switch of thermostats, I must say that it is a big coincidence.
Thanks for your input! I'll have a look.
IMO your should have a new refrigerator thermometer in the fresh food and freezer, and in any spare frig you might have. Check the temp at least 2 times a day morning and night.
What have the temps been averaging in both compartments?
I don't have the thermometers handy yet, but I will add this to the list of diagnostics. Thanks...