If a system has a defective compressor, finding a replacement is generally easy: Find the local wholesaler that handles the brand you need, give them the model number of the original compressor, and they sell you the same model compressor.

Occasionally, the original compressor model is not available, and you will need to cross it over to a replacement. Generally, the wholesaler does this for you, but since you are ultimately responsible for its installation and the operation of the system, you should verify the right compressor is being used.

When verifying a compressor, make sure the Btuh capacity of the replacement matches the original compressor’s Btuh capacity. It will likely not be exactly the same, but it should be reasonably close. Also verify the capacity of the replacement compressor, making sure you are referencing its capacity at the same evaporating and condensing temperatures as that of the original, because the Btuh capacity of a compressor will vary at differing evaporating and condensing temperatures. For example, at a 25˚F evaporator and a 120˚ condensing temperature, the capacity of a compressor may be 10,500 Btuh. But at a 10˚ evaporator and a 120˚ condensing temperature, the capacity of the same compressor may be only 3,490 Btuh.

Also verify that the replacement compressor can be used with the refrigerant used in the system. Compressors are generally designed to be used with a specific refrigerant or group of refrigerants, so make sure there is a match between the refrigerant and the replacement compressor.

Make sure the electrical characteristics of the replacement compressor match the original, including the voltage rating. This seems obvious, but it’s a potential mistake that I learned about the hard way. Many years ago, I installed a replacement compressor with the wrong voltage. Unfortunately, I did not realize the mistake until I had the replacement compressor connected to the system. Also, if you need a high-starting torque motor, then make sure the replacement is rated for a high-starting torque.

Look at the physical size of the replacement compressor, especially the height. The replacement compressor may look like it fits OK, but when you go to reinstall a cover, you may find it is no longer usable. This could be a deal breaker that goes unnoticed until after the compressor is installed.

Check the configuration of the compressor’s mounting plate. This may not be a deal breaker, but you might want to make sure that securing the compressor to its base will work. Check the compressor’s suction and discharge port locations and sizes. Matching this specification may also not be too big of a deal, but you may need to do a little repiping. However, if there is another option, it might make the installation a little easier.

With all the criteria that you need to match, it is obvious why it is always better to go with the same make and model when replacing a compressor. Since that is not always an option, we need to work with what we have by making sure that what we have will work.

Publication date: 4/1/2019

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