No one likes a warm refrigerator

By Sam Brown, Master Samurai Tech/Appliantology.org

When you’re a tech dealing with a warm refrigerator problem, the first question you need to answer is, “Am I dealing with a failed sealed system or a control problem?”

In other words, you need to half-split the problem between the sealed system and the controls (air movement, defrost system, temperature control, compressor start device, etc.). Let’s talk about three ways to half-split warm refrigerator problems.

1. Frost pattern

This is the venerable old-skool method where you tear down the freezer to expose the evaporator so you can see the frost pattern on the evaporator coil. A properly frosted evaporator coil will have a light coating of frost on most of the coils. Only the last rung or two will be frost free. The frosting parts of the coil is where your refrigeration effect is taking place: the refrigerant is boiling and changing phase from liquid to vapor. By the time it reaches the last two rungs, all the refrigerant is boiled off to vapor, so refrigeration is no longer taking place. 

The frost pattern also gives you information about other problems like incomplete defrosting, lack of airflow, air channeling, etc. All of these are control problems, not sealed system problems. For some problems, this is diagnostically useful information to know. But in the context of half-splitting between the sealed system and the controls, there are other, more clever ways to do this.

This is a favorite method of old-skool techs and techs who do not understand how sealed systems actually move heat around. That’s why you’ll see many techs reach for this method first. But there are cleverer ways to half-split the problem that do not rely on tearing down the freezer or installing valves. 

2. Compressor amps

In this method, you measure the running amps of the compressor. It can be very effective if you know what the normal running amps should be for that compressor. If you’re going to make an electrical measurement, you need a spec to compare it with to tell you what it means. You can’t use the locked rotor (LR) amps on the compressor label because this is the starting amps, which is much higher than the normal running amps. Sometimes the tech sheet will give a wattage spec for the compressor and you can convert this to an expected amp reading.

If amps are below a low normal, then you know the compressor is not doing as much work as it should. The reasons for this are usually either a weak pump or a refrigerant leak. Either way, this is usually a pretty good indicator of a sealed system problem if there’s normal heat transfer occurring at the evaporator; in other words, no evidence of the evaporator clogged with rime ice and the evaporator fan is running normally. As mentioned, the problem for the technician with this method is often knowing what the normal running amps should be. Running amps will also vary by a few tenths depending on the heat load on the evaporator coil.

This method gets muddier when you’re dealing with variable speed drive systems. You need the spec for compressor amps at full speed for this method to be useful with these systems. 

3. Condenser temperature split

This is by far the easiest and fastest method, and it requires zero teardown or fishing for compressor wires. It is also the least used by technicians because they are suspicious of it. The reason they don’t trust it is because they don’t understand the thermodynamics of sealed systems.

Condensers, like evaporators, are designed by the engineers to operate at a certain temperature split. The temperature split is defined as the actual coil temperature minus the ambient temperature. In condensers, the maximum condenser temperature split is 30 F. This means that with the system fully loaded with heat and normal heat transfer at the evaporator coil, you will measure a condenser temperature around 30 F above the room temperature.

But this is a design maximum, which you may or may not actually measure. In normal operation where compartment operating temperatures are being maintained, this split is typically less, maybe around 20 F or less. But the point is that in a normally functioning sealed system, the condenser will always be warmer than the ambient. You can measure this with an infrared temperature sensing gun in some condenser configurations or by using a thermocouple probe with putty to stick on the midpoint of the clean condenser coil.

Why is this split important? Well, if you’re going to remove heat from one compartment and reject it somewhere else, you have to have a difference in temperature to make heat move. The heat that’s picked up by the refrigerant in the evaporator must be transfered to the environment in the condenser. This means that the condenser must be warmer than the environment for heat. If the condenser coil never gets above room temperature, then this is positive proof that there’s a problem with the sealed system.

Want to learn how to troubleshoot refrigerators with confidence? Click here to check out our Advanced Refrigerator Repair course over at the Master Samurai Tech Academy. Be sure to use your BrandSource discount coupon, available in the Backroom, for 15% off your enrollment.

Sam Brown is “Professor of Appliance Repair Mastery” at BrandSource partner Master Samurai Tech (MST), an online training academy for appliance repair personnel, and is the administrator of its sister tech support site, Appliantology.org. For more information, email Sam at samuraitechhelp@gmail.com or call (603) 290-5516.

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