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A puzzling defrost thermostat question - Always closed, even at room temperature

john_in_fl_5646

Premium Member
Joined
Dec 2, 2022
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2
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USA
Part 1, but this isn't my question, just some background info: I have a Frigidaire FPBS2777RF0, that stopped working due to icing over, I believe from the door not swinging shut, and a couple episodes of hours with the door not fully closed. The coils were frozen so so much that the thermistor was pushed off of the coil by ice (the defrost thermostat stayed in place though.) It's back operational, probably not permanently, but it's working for the moment after defrosting with a hair dryer. (This isn't my current question, though.)

Part 2, this is my question: The defrost thermostat is the Frigidaire 5304521781, labeled as FR-5 57/43. According to everything I think I know, the specs say that it opens (continuity off (the clarifications are more for my brain than yours) at 57 degrees and closes (continuity on) (at 57 minus 43=14 degrees.

My question is this: I tested it, and it shows closed (continuity) at room temperature as well as cold (for the cold testing, I had it in the 7 degree freezer for several hours.) The part where it stayed closed at room temperature, I interpreted as a problem.

Except, I bought a new one, and the new one also shows closed at room temp too (as well as when cold.) I also found a post from someone else (dated a few years back) on another help forum, who had the same (exact) defrost thermostat, and that person had the same thing: Their old showed closed at room temperature, they bought a new one, and the new showed closed at room temp too.

It seems unlikely that a total of 4 different defrost thermostats (2 old and 2 new) from two different people (me and the other person) are all defective in the same way. I'm willing to say there must be something I'm not understanding?

I do have another question, but if you don't mind, let me begin with this question? I'm puzzled.
 
Well, I'll answer my own question: (groan). In this specific case, it's 57/43 CELSIUS, so 110/135 Farenheit. (Confirmed from reading the service data sheet.) In this case it's overheat prevention, and it's the thermistor/control board controlling defrosting.

Not that many thermostats list their numbers in Farenheit, and most operate in much lower temperature ranges. I suppose I should have noticed that the number didn't END in an "F".

Thanks in advance. Nice blog. Good advice here.
 
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