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My fridge stopped cooling - compressor was always off - so I tested if the thermostat could be the culprit by bypassing it - bang, compressor powered on. So I bought a new thermostat.

It is not looking identical to the previous one although it is listed as the official spare part.

I plugged all connection as in the old one (I pictured it) and compressor started pumping... forever. Fridge temperature went -8C and everything froze. Whilst, the internal light went off also when the door was open.

I thought that I probably connected the cables to the wrong connectors - so that when the fridge senses too cold, it stop powering... ehm, the light.

Still, I can't get around it. I own a multimeter. How could I use it to test what are the proper connections so that the thermostat will stop powering the compressor rather than the light?

Assuming that my idea about those connections is right, and it could be not.

enter image description here enter image description here
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Including the make and model of the refrigerator (and the part number of the replacement thermostat), would make answering this question much easier. Without this information, the answer is "Use the mulitmeter to trace the wires to their destination.". –  Tester101 Sep 17 '13 at 12:14
    
@Tester101 getting suggestions about how to use the multimeter to trace the wires would be of great help! I will add all of the infos as soon as I will get back home. –  Dakatine Sep 17 '13 at 13:07
    
The fridge is an Electrolux ER 3404 B. The thermostat reads "Ranco" and - hey - a load of other things. I guess those are the descriptors of the pins. I'll try to figure out them. –  Dakatine Sep 17 '13 at 16:07
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1 Answer

up vote 2 down vote accepted

This is the simplest thermostat you will get. It has 4 pins on it.

  • 2 of which will be GND and Vcc
  • 1 will turn on and off (the compressor and other stuff)
  • 1 will be the sensor.

enter image description here

Easiest way to test which is the sensor and which is the switch will be to test continuity on the pins. Set your multimeter to ohm. Place one probe on GND and the other on one of the 2 suspected pins (senors, switch)

  • The switch will usually be closed- so no ohm reading (no route)
  • The sensor will give you some ohm reading (5~50)
  • GND will give you 0ohm (Short)
  • Vcc will give you and ohm reading again.(this one can get confused with the sensor.

They should be pretty clearly marked to be honest. Are you sure that the thermostat has not been set to the lowest setting? Maybe the sensor is misinterpreting the thermostat.

The other way to test it is the Live way. This is dangerous so if you do not have gloves and insulated tools, or unsure of the voltage do not attempt this. Have somebody with you to turn off power in case of emergency.

  • Adjust the thermostat to the lowest level (warmest inside - or like 0/10)
  • Test voltage on the pins and turn up the thermostat slowly
  • Keep reading until the voltage goes on or off
  • Try the next pin the same way.
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Thank you man. I still have some doubts though. You mention VCC at a point. Is that the compressor, right? –  Dakatine Sep 17 '13 at 15:54
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Sorry Vcc refers to the positive voltage. Vee is negative just so you know but not really used any where. This voltage may be 220 Volts or 12 Volts - SO be careful. FYI: Vdd/Vss is used in logical circuits like a computer equipment and stuff. –  ppumkin Sep 17 '13 at 16:00
    
Either case, I cannot read any value. I get 0 when I short ground with ground - OK - but I get "out of limit" for the other pins no matter the range I set on the multimeter (it is not auto-ranging). I checked the multimeter against a resistor I own and it read the correct value so I guess the multimeter is fine. I'll try the next way when wife will be back home. :) –  Dakatine Sep 17 '13 at 16:00
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When testing voltages switch between AC/DC. It is most likely AC so insulate yourself and do not touch any bare metal of your equipment or fridge. 0ohm means dead short(no resistance) which is expected of GND to GND. Use GND as reference for other pins. –  ppumkin Sep 17 '13 at 16:02
    
Any luck with that? –  ppumkin Sep 23 '13 at 11:55
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