Some refrigerators use a mechanical cold control like this one:
for regulating the temperature inside the compartments. These controls have a feeler capillary tube attached to the body of the cold control. Inside the body, changes in temperature, as picked up by the capillary tube, cause the bellows to expand and contract which, in turn, causes a set of electrical contacts to open and close. These contacts control the line power to the compressor and need to be closed for the compressor to run.
When troubleshooting a refrigerator that's warming up and you notice the compressor isn't running, one of the things you'll need to check the cold control. You could check continuity of the contacts and think the control is good but beware the adage that's been indelibly etched into the minds and hearts of all seasoned appliantological warriors: Ohms checking is merely preliminary-- something can check good on ohms and still be bad. Never accept an ohms check as conclusive proof that something is good.
Professor Willie offers some additional insight into the failure modes of mechanical cold controls:
That is actually one of the more common failure modes of a cold control to be intermittent.
If you pull the old one apart after you replace it, I can pretty much guarantee that you will find the contact points look quite crispy and melted.
One good way to know this is your problem is when you find that the unit it off and starting to thaw out, don't turn or touch the control dial, just give the control area a good slap and if it starts when you do that you can be pretty much assured you have a bad cold control, (the jolt or turning it up or off/on will make the contacts connect again until it opens and tries to close on its own).
Every now and then, you run into a real CF when you're trying to order a part to fix an appliance. A case in point is trying to get a start relay kit for some models of LG refrigerators, such as the LFX25960ST.
Grand Master kdog, adept extroidinaire of all things appliance repair, explains how to de-frak this mess:
I had the exact issue with the same model # before - this got me out of it.
The components do not all show up on the literature - at the time I was working for a very large company that had alot of pull with LG and I begged them to contact LG to correct this issue for future folks that get caught.
I did not replace the capacitor as it was not required
One of the prongs on the relay will just be unused - no biggie, I knew this because i was sent to the fridge with a control board that had been ordered and overnighted (very costly delivery) - just to find out there was no issue with the board, can't just look at the lady and say I need to order parts again (no fridge!), rummage around in truck and find replacement by eyeball matchup (no app for that).
I should expand on that a bit - I recognized the particular model of Embraco compressor that I have seen many times in W/P built fridges and went from there.
A common problem with refrigerators is the appearance of various forms of water in places where it shouldn’t be. Examples are: water at the bottom of the freezer and dribbling out the door in a side by side refrigerator; fuzzy frost built up on the back wall inside the freezer compartment; moisture on beer bottles and the side walls inside the refrigerator compartment (also called the Beer Compartment); solid slab of ice on the bottom of the freezer compartment.
In each of these examples, we’re dealing with water that’s out of place. Water in a refrigerated space can take on three forms: ice, frost, and condensation. Which of these forms you see, along with where you see it, are important clues to help you zero in on the needed repair.
Condensation problems will appear as “sweating” on jars and bottles and sometimes even on the sidewall in the refrigerator compartment. Condensation is caused by water vapor condensing into a liquid as it hits the cold surfaces inside the refrigerator. When you see this, it means outside, humid air is getting inside the refrigerated compartments when and where it shouldn’t. So, you’re looking for bad gaskets, doors not closing properly, or doors being left open from carelessness.
Ice refers to liquid water that froze into a solid. This sounds obvious but it’s an important distinction from frost, also known as rime ice, that fuzzy looking stuff that is formed when water vapor condenses directly into a solid. The important point here is that ice and frost are the effects of two completely different underlying causes.
If you see smooth or solid ice in a freezer, then you know you’re really looking for liquid water in places where it shouldn’t be (that ended up freezing): clogged condensate drain in the drip trough below the evaporator coil; ice maker fill tube leaking or out of place; ice maker mold leaking.
If you see frost or rime ice in a freezer, then you know you’re really looking for water vapor that’s getting into the compartment. How does water vapor get into a refrigerator? It comes in with the outside air. In most cases when you see frost in a freezer, you’re looking for an air leak: bad door gaskets or doors not closing all the way. This video shows an extreme example of rime ice all over the contents inside a freezer:
Sometimes, you’ll see both ice and frost appearing together in a freezer which can make diagnosis tricky. In this video, I walk you through an example of such a case and I explain the failure sequence:
A special (but common) case for diagnosing frost in a freezer is when you see frost accumulated on the evaporator coil or back wall inside the freezer that covers the evaporator coil. This indicates a defrost system failure (defrost terminator stuck open, burned out defrost heater, bad defrost timer (on older units) or adaptive defrost control (ADC) board).
The reason rime ice forms on the evaporator coil in the first place is because the coil operates at a temperature of -20F. At that temperature, water vapor that contacts the coil will condense and freeze directly into a solid, forming rime ice. Every few hours the defrost system should kick in and melt that ice, because if it’s allowed to accumulate it will eventually act as an insulator, preventing the air from contacting the evaporator coils and getting cold. The resulting problem would first be seen as a warm refrigerator compartment and, if allowed to continue, eventually the freezer will also get warmer than normal (normal = 0F). Rime ice accumulated on the inside of the back wall in the freezer will often be seen at this point.
This melted rime ice has a special name: condensate. (Not to be confused with condensation, although the words are similar, they arise from two different causes.) Condensate refers to the water that gets melted off the evaporator coil in the freezer compartment during the defrost cycle. This condensate drips onto the condensate drip trough below the evaporator coil and drains out the condensate drain– a hole in the condensate drip trough– through a tube to the drain pan placed down by the compressor where it eventually evaporates due to the combined action of the compressor heat and condenser fan motor.
This video shows a freezer with extreme rime ice buildup on the back wall inside the freezer due to a defrost system failure:
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As professional Appliantologists, we've all run into situations where we realized that we needed a way to log temperature data inside a refrigerator for at least 24 hours to get a clear picture of what's going on inside that box. A couple of examples are:
Customer complains of warm temperatures in the beer compartment of her Maytag side-by-side refrigerator but says that the freezer compartment is fine (and we know how accurate customer temperature measurements are... NOT!). You arrive and measure the freezer temperature using your infrared temperature gun and get readings that vary from +5F to +12F. Marginal temperatures for a freezer but was that because it was just coming out of a defrost or off-cycle? Was the door recently opened just before you got there? You don't know and all you have is the one data point: the measurement you just made. Wouldn't it help your diagnosis if you could put a data logger inside the freezer for a day or so and then look at a graph of the actual temperature measurements inside that freezer over time?
Customer complains that the freezer temperature in her GE built-in refrigerator fluctuates over time from 5F to 10F to 20F and then back to hard freeze. You maybe even verified this yourself (if you spent enough time there to do this). But how much time in a typical service call day do you have to babysit freezer temperatures? And you still wouldn't be able to gather enough temperature-time data points to discern whether or not there's a pattern to the fluctuations which could then be correlated to some other process in the refrigerator (defrost cycles, compressor cycles, etc.). Even seeing that there is no pattern, that the fluctuations are random, is also helpful because it could indicate something as simple as the door not being closed all the way (hinge adjustment issue?).
See what I be sayin', mah bruvah? In cases like these (and many others-- I'm sure you can think of several that you've been on), you just gotsta be able to look at the temperature inside the compartment over an extended period of time. Enter the Supco LT2 LOGiT Dual Channel Temperature Data Logger:
Which needs the Supco LOGiT software package to enable it to connect to your Windows PC to set it up and download the data:
...and it all works AWESOMELY! Here's a video I made showing you how to set up and use the LT2 and the type of temperature profile graph it generates:
Since I am a Mac user who (until recently) didn't own a Windows PC, the above two items necessitated the purchase of my first Windows PC in over seven years! Turns out this was not as expensive a proposition as it sounds.