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ukcommando
03-01-2008, 07:56 PM
I've just replaced the freezer and evaporator thermistors in my Mistral Fridge/Freezer to fix the common problem with loss of cooling in the fridge (as described at length on many other threads here)

I thought I'd take the opportunity to measure the resistance of the old and new thermistors to see if there was any hint of which was at fault. The values I measured (at room temperature) were:

Yellow (evaporator) Old 3.7kohm New 4.34kohm
Green (freezer) Old 3.7kohm New 3.7kohm

This does make me wonder if it was the yellow thermistor at fault in my case. I know that this is a rather simplistic test, but it would be interesting to see if anyone can corroborate with their own readings. Has anyone else had the opportunity to do measurements like this? Reason for asking is that if the repair can be limited to replacing just the one component rather than two, it all helps, especially considering the rather low value of second hand fridge/freezers anyway.

Cheers

Dave

Brian_UK
04-01-2008, 01:16 AM
Dave, you could well be right.

It doesn't take a lot to confuse the controls when a sensor starts reading incorrectly. Depending on the type of sensor then the temperature offset from that expected can be quite large.

A set a tables from Honeywell, here....

http://content.honeywell.com/sensing/prodinfo/thermistors/resistancetables.asp

can show the different temperatures against resistance.

paul_h
04-01-2008, 10:13 AM
Plug the sensor in, turn the fridge on and compare volts.
I repair a certain brand which has thermistors failing a lot. Sometimes it shows up when reading resistance, but a lot of times it doesn't, it only shows up when plugged in and reading the voltage across the thermistor.

daveflower
06-01-2008, 08:56 PM
the problem isn't with the sensors, but with their connection on the rear wall of freezer, moisture builds up during defrost cycles and corrodes connections to the point where they build their own resistance, and thus changes the reading the pcb gets, and therefore affects the operation of all components. You can try cleaning the contacts, but in my years of experience it never works for very long. It is far better to replace both. Latter units featured covered terminal blocks to shield from moisture deposits during defrost.
Hope this answers your question.

stan4928
22-02-2010, 09:47 PM
I have just checked the door on my fridge compartment and noticed how much the door had dropped, and then fridge started up! I going to run it for a while to see what happens to temp, and will post an update. If its a case of adjusting door hinges will keep u posted...

Dave M

stan4928
23-02-2010, 07:20 PM
Over the moon, it was the problem with the fridge door that had sagged enough from the push switch which kept the light on when the door was shut, where the temperature went upto +22. saced myse;f money as i was about to get on the phone and but 2 thermistors. I read a small thread from another fridge problem and that was the same problem as mine. Misatral Plus is working perfectly and saved me a fortune!!!
It may be the same with other problems i have seen on these thread? Sherlock and Watson would have been impressed!!
Bye for now over the moon (sad i know) but relieved!!

Dave M:D