Vitrifrigo service tip: misbehavior due to thermostat fault

[dbostrom]

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Just as a "for the books" note for anybody who might be facing this problem in the future. 

Our refrigerator was "short cycling" in way that caused me concern for the compressor's health, given that the refrigerator's controller monitors such  things and will cut off the compressor if things are going wrong. The symptom: on/off/on/off at approximately 2-3 minute intervals. By ear, one could hear that the evaporant loop was barely reaching stability before the unit kicked off. 

As well, the thermostat needed to be turned "all the way to 11" in order to maintain useful cooling. 

Before tearing into the compressor and given that the refrigerator was able to maintain temperature (albeit in an unusual fashion),I decided to first "shotgun" peripherals "just in case." Peripherals are not very expensive and are easy to swap and this boat's duty doesn't permit a lot of tools-in-hand-chin-scratching.

• As it turns out, the thermostat was the culprit. The bimetallic had aged such that the refrigerator was attempting to stay within a very narrow temperature band, as opposed to maintaining a temperature swing range between "on" and "off."  In geek-speak, the thermostat's hysteresis "dead band" had pretty much vanished. 
  
  
• A side-benefit: the replacement controller that I didn't actually need was nonetheless beneficial to swap in, because it wastes about 1/2A less juice (notably, the new model controller is missing a substantial heat sink found on the old version, because it's not wasting juice into heat from semiconductors). The old controller is now tucked away as a spare. 

It hardly bears repeating but it's quite harmful for the compressor to be operated this way, and of course this mode is going to have a fairly nasty impact on electrical consumption. So, maybe worth tracking this in a loose sort of way; "does the refrigerator seem to be cycling more than it used to, all things being equal?"

The age of this equipment is ~12 years as of this date, with refrigeration in constant service for 7 months of each of those years. No complaints on reliability. 

Cheers!

[dbostrom]

Two other little things that are helpful to know, probably well known to many:

• It may seem as though a third almost-impossible-to-reach screw behind the thermostat needs to be undone in order to remove the thermostat. Do note that the rear fastener bracket is slotted, so it's unnecessary to remove that screw. For the very dense (me, for instance) this was not immediately obvious. Thankfully I eventually used my phone camera to take a picture before going to extreme measures. 
  

• The controller is fastened to the compressor and is awkward/impossible to remove/replace "in situ." As it turns out, releasing two screws on the inboard end of the compressor "tray" allows the entire affair to be slid into the space beneath the sink. There is ample tubing provided for this extension, although it's still a good idea to avoid straining/kinking the tubing while moving the compressor tray. 
  

[Trevor]

Many thanks for that post Dbostrom,

That is a really great explanation and may explain why my system seems to short cycle a bit. I guess when the time comes it might be a good reason to consider an electronic thermostat to replace the current "mechanical type". Some of us like to keep things original however.

Anyway thanks for sharing.

Trevor