Most commercial grade freezers made prior to 2006 will have semi-hermetic compressors in them. Compressors are sized according to the horse power of the compressor, the electrical requirements, and engineering specs sized to accommodate the needs of the unit.
EXAMPLE of semi-hermetic units:
* Most 3-door freezers will have a 1.5 hp compressor
* Most single door freezers will have 3/4 hp compressor
* 2-door freezers can have 3/4 hp - 1.5 hp depending on the brand of the unit as well as whether it is a glass door display freezer or a solid door / stainless steel freezer

To determine the size of you compressor is as simple as understanding the numbers in the serial number.




Breaking this down =
1. THE KATB is the model of the compressor - factory coded and also determines the size of the pistons, valves, etc.

2. THE 015A is the rated horse power of the compressor. In this case the 015 = 1 1/2 hp along with the type of oil "A" (if any) when shipped. The "A" here stand for Alkyl Benzine. A "N" would mean "none" or that the unit was shipped dry - with no oil. If the letter following the hp was an "E" this would stand for or mean Poly-o-ester commonly known as Ester oil.

3. THE CAV is the electrical requirements. In this case, the CAV stands for 230 volt whereas CAA would = 115 volt.

4. THE 800 is a factory code

Let's do another example:


Breaking this down:
1. KAMB is the model of the compressor - factory coded and also determines the size of the pistons, valves, etc

2. THE 007E is the horsepower of the compressor (3/4 hp smaller)and the "E" is the oil type and in this case it was shipped with "Ester" oil OR Poly-o-ester (POE) oil.

3. THE CAA is the electrical requirements and in this case it stands for 115 volt power from single phase

4. THE 224 again is a factor code or designation


It is imperative to keep the factory original compressor sized for each unit. These compressors ARE NOT interchangeable. For instance; you would NOT want to take a 1 hp compressor out of a Beverage Air Freezer for example and replace it with a 1.5 hp thinking you could possibly make the freezer colder or work better. Each manufacturer has engineered the proper size, hp, etc., compressor for the particular set up. There are so many variables that actually determine the sizing and horsepower it would take an engineering degree to explain them all. Bottom line: DO NOT interchange compressors - ALWAYS install factory recommended compressors.


There are several advantages with the semi-hermetic compressor with only a few minor short comings.

For starters, the semi-hermetic is completely re-buildable. Whereas the opposing "tin can" compressors are disposable, the semi-hermetic can last a lifetime if properly maintained.

I also personally prefer these compressors in the field as there are many things that can be repaired on site with proper diagnostics.

More times then not, a simple valve plate replacement and an oil change can extend the life of a tired compressor.

The disadvantages are more cost related then anything else. For example a "new" replacement factory original compressor can run upwards of $2,000.00 (cost to customer not including labor to install) whereas a re-manufactured compressor can run as high as $1,500.00 if properly shopped.

Another issue for some is the excessive weight of the semi-hermetic. These compressors are extremely heavy and outweigh the "tin can" counter part by at least 4 to 1


The second alternative for compressors is a hermetic compressor and it is commonly referred to as a "tincan". The tincan is a balanced and sealed unit that is disposable in that it cannot effectively or efficiently be rebuilt.

Many freezer manufacturers are converting to these hermetic compressors for energy standards. In fact, almost all manufacturers after 2006 will have completely changed over to the hermetic compressor.

So what are the advantages / disadvantages of each....

The hermetic compressor does seem to pull temperature faster than the semi-hermetic. I have set (2) Master Bilt BLG48's side by side; one with the hermetic, the second with the semi-hermetic. Every single cycle, the hermetic outperforms the semi-hermetic.
The compressors each have a unique and different sound to them. The semi-hermetic sounds more like a car engine with it's pumping action sound.

Conversely, the hermetic compressor has a higher pitch factory squealing type noise to it.

As stated earlier, both are great units, but with technological advancements, engineers have chosen this new hermetic compressor over the traditional semi-hermetic.

NOTE: The semi-hermetic can be rebuilt while the hermetic cannot cost effectively be rebuilt.

Compressor Oils

As pointed out above, compressor come with different types of oil. These oils need to be compatible with the refrigerant used in the individual piece of equipment. Currently there are three basic types of oils being used in the industry and four codes stamped on new compressors.

"O" = mineral Oil

"A" = Alkaline Benzine Oil

"E" = Ester or Poly-o-ester Oil

"N" = none - the unit was shipped without oil. (this is important to know prior to installation and start up)

In semi-hermetic compressors we can easily check the oil level, check the condition of the oil, change the oil, and even change out the oil.

So why would someone want to change the type of oil being used? This is an excellent question. The only reason to change for instance from Alkaline to Ester Oil would be when we are changing refrigerants or the temp. of the unit we are working.

You see, many compressor, for example that are used for walk-ins are able to be low or mid temperature units simply by deciding which refrigerant to use. Thus, once we decide which is the preferred refrigerant, we can decide which is the necessary oil.

What about tin cans / hermetic compressors? Truth is, there is no real easy way to change the oil in a hermetic compressor. I am not saying it can not be done, because it certainly can if you so desired, I am just saying it is not easy and not practical.

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