Samsung Refrigerator RS2555SL - freezer drain heater impedance - bimetal operation opposite normal - hot ice maker?

[Badbrad1]

Hi, have a Samsung RS2555SL and am well familiar with fixing its' many problems (and refrigeration generally). I have 3 problems/questions and would greatly appreciate the experienced wisdom of those on this forum. Thanks in advance if anyone would help.

Its' current problem was an ice clogged freezer evap. This occurred because the bimetal and defrost fuse blew, but not before melting a bunch of the styrofoam and plastic of the freezer evap cover (I've molded new styrofoam and heat-gun-fixed the plastic)! I thought the fuse/bimetal was supposed to blow BEFORE anything got hot enough to melt???

I have a service manual, and "Fast Track Troubleshooting" pdf for this model (but I've found them to be sometimes woefully inadequate for troubleshooting this fridge, eg. the schematic in the manual is different than on the back of the fridge, and some circuits are not even illustrated/mentioned!!! I understand why technicians don't like to work on Samsungs!).

First question: the bimetal. I have a new freezer defrost fuse (it tests properly with continuity). I have a new bimetal thermostat, but it doesn't test properly and can't find anything specific to this model (or in the manual). I understand bimetals are supposed to have continuity when cold, but open when warm. This new one seemingly doesn't ever open, no matter what temp (have frozen it in freezer and heated with a hair dryer), so can I assume it is DOA - OR does it work opposite a normal bimetal circuit? I ask because it is wired in parallel with the freezer temp thermistor. Am I correct that normally, this bimetal is open when cold; but when this bimetal is heated (defrost cycle), it closes, sending a signal to the mainboard that appears the temp thermistor is very low in impedance (has continuity/shorted) and thus very high in temperature so the mainboard, seeing a temp over 150 degrees - will shut off the freezer defrost element circuit? (service manual pg.30, #09).

Second question: the freezer drain heater. There is no troubleshooting info in the manual, can't find any online, and even the replacement part is very scarce. What is the impedance supposed to be for this heater? Mine measures at about 1.6 megohms initially and slowly climbs as the meter is attached, slowing around 4 megohms. In the "Fast Track Troubleshooting" pdf (the only place I've seen anything close to a value for this), it says "320", but no scale (ohms, k ohms, M ohms, etc.). Does anyone know what this drain heater should test at?

Third question: hot ice maker? Leading up to this problem, it had been melting ice cubes periodically. I felt the front of the icemaker cover (over the motor/gears/micro-switches), and it was very warm. I understand now that there is a water pipe heater in the roof of the icemaker cavity (tests at 2.61k ohms). Does anyone know why this would have gotten so warm/hot during the defrost cycles, and what the shutoff mechanism is supposed to be (is it supposed to be the ice cube tray thermistor sending a hi-temp signal to the mainboard?)? Mine tests 4.83 k ohms @78 deg.F, so appears in range. Why would this cavity have gotten so warm (even hot) without shutting off? Faulty mainboard? (also, what is the voltage for the ice cube tray motor? I want to test this with a power supply before re-assembling the fridge).

Lastly, any comments about this: I have no continuity for one of the freezer heater element wires - to #13 - CN70 mainboard connector (orange wire). It appears the wire is burnt out, probably because of the failure of the bimetal and temp fuse to blow early enough (which caused the extreme heat to melt the styrofoam off and the warp/shrink the plastic of the evap fan holder/bracket). I am going to do surgery on it: cut the back open (width of the back and 18" high), cut the foam out where the freezer wiring connections are, and pull a new wire through to replace this - from the mainboard to the freezer heater element connector. I'll re-foam, pop rivet/flange the back and seal with metal tape. I surmise there may be various "thoughts" so please temper your comment to this? I'm retired, a life-long jack-of-literally-all-trades, and enjoy the challenge of fixing/fabricating just about anything. Sure, we can afford to buy a new fridge (and probably will after I get this one working again - wife would like a french door style, but yes, no Samsung or LG! Probably Maytag or Frigidaire?) (but why would anyone want to subject themselves to the torture of yet another of these problem-prone, poorly engineered, planned obsolescence, "new fridges"?), but I've always repaired things instead of throwing them away, if economically viable and they still can do the job.

Thanks very much for your reasoned assistance with these 3 questions. Strangely, with all the Samsung trouble reported on the web, I've not been able to find a definitive answer to these questions. I'd greatly appreciate your help!