Actron AM24-1 Controller Possible Thermistor Replacement.

[wotnot]

Hmmm....as you've noted a discrepancy between the temp the unit now displays (as opposed to previously), and what temp is measured by standalone thermometer, one has to make a choice on which data-points might be deemed as accurate.

If we consider the multimeter reading to be accurate with 8K resistance, we'll guess at one of the more common thermistor values (10K @ 25C);

(what the unit says)-> 8K @ 20C would infer a 10K NTC thermistor @25C with a delta of 3.9% per degree C

(what the thermometer says) -- 8K @ 23C ...nothing really 'fits' the standard ranges ..8K2 is the next resistance value down but none have a low enough thermal coefficient, ergo it's likely a 10K @ 25C NTC as well , with a higher delta value...highest I can find is 4.7% per degree C.

'Just because' the component itself is unmarked, and you've noticed a discrepancy between two different controller boards wrt measuring temperature (with the same unmarked thermistors) -and- your controller has already lunched on one, you're allowed to speculate these thermistors are chinese bespoke, or else factory rejects, or anything else like this, and thus if something like the actual component tolerance is out to +/-20% instead of less than half that, these things would easily account for such discrepancies (and the fact they die in the first place =)

Of the 2 choices, I'll presume the unit is working in some uncalibrated state due to the board swap, but the part dimensions appear correct wrt thermistor types... ergo, replace dead thermistor with any NTC 10K @ 25C thermistor, and observe results... ie; how closely displayed temp correlates with thermometer readings.