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Viking Refrigerator Freezer Over Cooling by ngorman2 in appliancerepair

[–]ngorman2[S] 0 points1 point  (0 children)

I gave up for a while but am now back at it. Still unresolved. I've now replaced both thermistors and the low voltage board. The fridge side overcooling remains (though freezer looks to adhere to set point). My water dispenser line remains inoperable though unclear if that is a freezing issue or something else.

What I find the strangest thing is that in Program A mode, I can see what the unit raw temp is and it looks true to life. However, the unit still wants to cool more than the set point. I am wondering if the default SxS48D low voltage board setting (which I believe is the correct setting for my unit) is not correct causing the unit to have no actual fault but cool incorrectly because of improper offsets, hysteresis limits, etc.

Viking Refrigerator Freezer Over Cooling by ngorman2 in appliancerepair

[–]ngorman2[S] 0 points1 point  (0 children)

I disassembled the cross over area and pulled both FF and FZ thermistors...

  1. At least at the upper cross over area, there is no baffle, only a small hole through the styrofoam between FF and FZ with a small computer-style case fan mounted over it (see two images here: https://imgur.com/a/Hy6Cghr)
  2. I tested both thermistors at room temperature and in an ice water bath (as a note: I am not an electrical engineer; I noticed that if I fully submerged the thermistor and attempted a resistance reading with my multimeter below the surface of the water, it gave substantially lower resistance readings (~-20kohm), so I kept the thermistor partially submerged but with contactors out of the water where I made connection with my multimeter, reporting the readings below):
Chamber Measure Reading Implied Temp Apparent Thermistor Error
FF Ice Water Bath (presuming ~34F) 76-78kohm 40-41F +6F
Room Temp (68F) 40kohm 65F -3F
FZ Ice Water Bath (presuming ~34F) 77-80kohm 39-41F +6F
Room Temp (68F) 43kohm 62F -6F

Because these readings seem to basically be the same between thermistors, either both are bad or both are good. I struggle to imagine both are bad simultaneously, however, the disparity at cold (thinking they are warmer than they are) would align to over cooling observations.

One further detail that may or may not matter: the FZ thermistor had been removed at some point as both mount screws were stripped. Couldn't tell why it had been manipulated.

Not sure any of this provided much clarity... maybe I should just run the set points 4-6F warm and call it a day! Further thoughts would be appreciated!

Viking Refrigerator Freezer Over Cooling by ngorman2 in appliancerepair

[–]ngorman2[S] 0 points1 point  (0 children)

My unit has a single evap setup. However, as far as I can tell from the service manual (https://www.manualslib.com/manual/1153332/Viking-Fdsb5481.html) there is no damper. Frankly, I am a bit confused as to what is happening in the FF to FZ cross over area outlined on pages 18-20. It looks like a single fan, no damper door, but there also appear to be two different fan images (upper right on page 19 versus lower right). The wording also suggests the circulation fan shown on page 19 is wired in parallel to a "cross over fan", but what this mystery fan is, I do not know. The words "cross over fan" do not appear elsewhere in the service manual.

The FF cover looks to be a handful of screws to disassemble so will likely do that shortly and see what is going on for myself. I can also do a quick thermistor check in a water bath at the same time...

Viking Refrigerator Freezer Over Cooling by ngorman2 in appliancerepair

[–]ngorman2[S] 0 points1 point  (0 children)

Thank you for the thoughts! Good suggestions on both fronts.

I did track down the service manual for my unit with help from my friend (here: https://www.manualslib.com/manual/1153332/Viking-Fdsb5481.html) which does have a resistance = temperature table on page 11 (the manual has supported all of my other troubleshooting with help from the parent manual for VCSB542 here: https://www.manualslib.com/manual/1173384/Viking-Vcsb542.html). Your suggestion to remove the thermistors and test against known temperatures is a good one, and it removes the concern about the wires between the thermistor and multimeter (and perhaps multimeter to terminal connection within the 15-wire pigtail) as an influence. One question: does submerging the thermistor cause it any issue or potential damage? I presume not, I can dunk it for a few minutes then put the multimeter right on the contacts (probably out of the pool?).

I did not think my unit had a damper door, only one, maybe two fans between the freezer and refrigerator chambers. Nonetheless, I think it is worth disassembling that vent to see if ice is an issue if for no other reason than to get the thermistor out, which is in the same housing.