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Appliance Repair Tech Tips

A blog by Son of Samurai in General

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One Magic Trick to Instantly Identify Sealed System Problems

Son of Samurai

Entry posted by Son of Samurai

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One of the first steps when you're troubleshooting a warm temperature proble in both compartments of a refrigerator should always be to identify whether you're dealing with a problem in the sealed system or with a problem elsewhere in the unit.

The go-to method for most techs is to get eyes on the evaporator coils. While the frost pattern there can tell you a lot of things about the health of the refrigerator, it has a massive drawback: getting to the evaporator can require a lot of non-trivial disassembly, including emptying the entire compartment.

There has to be an easier, smarter way to identify a sealed system problem right?

Of course there is! All you have to do is take a temperature reading on the condenser coils. It's that simple. Or rather, it's that simple if you know your thermodynamics.

To perform this test, you'll want to get an accurate temperature reading on the middle of the condenser coils, since that's where the refrigerant is at saturation. If you can get this with an IR gun, great; if not, you can use thermocouples. In a healthy system, you should measure at least 20F above the ambient temperature. A reading of less than that 20F temperature split indicates that you have a sealed system problem without any doubts. 

A reading of a 20F or larger temperature split suggests that the sealed system is working within spec, but it does not prove it. Think of this test like an ohms measurement -- if the measurement results are out of spec, you know it's bad. If they're in spec, you don't necessarily know anything, and further testing is required.

So there you have it: one easy, nifty little test that lets you positively identify a sealed system issue with minimal disassembly. Want to learn more about how to troubleshoot refrigerators and sealed systems like a wizard? Check out our refrigerator repair course over at Master Samurai Tech.

If you're a premium member at Appliantology, you can also enrich your thermodynamical know-how by watching our series of webinars on the subject. Click here to watch: https://appliantology.org/announcement/33-webinar-recordings-index-page/

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SC2015

Great post Son of Samurai!  

I have found a least one customer who found such a simple diagnosis hard to swallow, we ended pulling the evaporator cover anyway. 

Some of our techs also work on HVACR and its the same refrigeration cycle there (obviously!) a sure sign of a sealed system issue is a lack of heat in the condenser: No heat, no pressure. 

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Son of Samurai

Son of Samurai

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On 12/2/2019 at 9:39 AM, SC2015 said:

I have found a least one customer who found such a simple diagnosis hard to swallow, we ended pulling the evaporator cover anyway.

I've heard of other guys having similar problems when doing this test. It really comes down to the age-old issue of customer perception. You've got to convince them that you, as the technician, know the specs and can interpret what different measurements mean.

Sometimes it helps to ham it up a little -- do a few other temperature measurements as "confirming tests", mention how expensive and refined your thermocouple is, etc. You can also try explaining to the customer in simple terms how the thermodynamics of the system works: if the condenser isn't rejecting enough heat, that means the evaporator isn't absorbing enough heat.

It's all a tricky business. Sometimes I think that managing customer expectations is harder than anything on the technical side of the trade!

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Son of Samurai

Son of Samurai

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4 hours ago, 16345Ed said:

Samurai always told us 30 degrees before, did he not?

Good memory! The design spec for the temperature split is indeed a 30 degree split. That's the design assumption that the engineers used to size all the components.

However, the actual temperature split will fluctuate based on the actual operation of the unit. That's why we allow for a margin of error by saying that the sealed system is only definitively out of spec if the temps read below a 20 degree split.

A good trick if you want to make sure your split measurement is as accurate as possible: open the freezer door for a minute or so before taking the measurement. That will get the temperature split as close to the spec as possible.

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