Determining Compressor Amperage Ratings

July 31, 2003
/ Print / Reprints /
ShareMore
/ Text Size+
When you are diagnosing a potential compressor problem, you need to measure its amp draw to get a correct assessment of its vital signs.

The best way to determine the correct amperage draw for a particular compressor is by referring to the rating chart for that compressor.

Compressor manufacturers publish a rating chart for each compressor they manufacture. The compressor chart will list the correct amp draw for the compressor under its various operating conditions.

To use the chart, the technician must know the evaporating temperature, condensing temperature, and voltage applied to the compressor. A technician can determine the correct amp draw for the compressor and use that information to accurately troubleshoot the compressor and the system. With the use of the Internet this information is now easier to obtain.

Why Not RLA?

Most compressor manufacturers will stamp an amperage rating on their compressors. They will usually stamp the Rated Load Amp (RLA) of the compressor. However, the technician cannot use this value to determine the correct operating amperage.

Also, trying to determine if a compressor is good or bad using RLA is not correct. It has nothing to do with what the correct amperage draw should be under its various load conditions.

RLA is a mathematical calculation required to meet Underwriters Laboratories (UL) approval. The compressor manufacturer must run a series of tests to determine the Maximum Continuous Amps (MCA) before the overload trips. Once that has been determined, UL says to divide the MCA by 1.56 to determine the RLA. Some compressor manufacturers, such as Copeland and Carlyle, use a different factor. They divide the MCA by 1.44.

If the RLA has any value, it is to determine at what amperage draw the compressor overload will trip, and to determine the fuse/circuit breaker size and the wire size.

Amp Measurements

When measuring the amp draw of a compressor, make sure to read only the amperage drawn by the compressor. Choose a location on the wiring diagram that will isolate the compressor from any other loads, such as the condensing fan motor.

It is important to measure the amp draw of the compressor only when you are trying to determine if it is operating properly.

Often a system problem may seem to be the result of a defective compressor when in fact it is due to some other cause. Using the amperage draw of the compressor will help any technician determine if the compressor is truly defective.

However, the technician must know what the correct amperage should be.

Joe Marchese is owner of Coldtronics of Pittsburgh. He can be reached at 412-734-4433, www.coldtronics.com, or joe@coldtronics.com.

Publication date: 08/04/2003

Did you enjoy this article? Click here to subscribe to The NEWS Magazine

You must login or register in order to post a comment.

Multimedia

Videos

Image Galleries

2014 World Energy Engineering Congress

Scenes from the 2014 World Energy Engineering Congress in Washington, D.C.

Podcasts

NEWSMakers: Matt Barga

Matt Barga, portfolio manager — a/c and coils, Ingersoll Rand, discusses how the company is working to comply with the new energy conservation standards for heat pumps and air conditioners that go into effect on Jan. 1, 2015. Posted on Dec. 19.

More Podcasts

ACHRNEWS

NEWS 12-15-14 cover

2014 December 15

Check out the weekly edition of The NEWS today!

Table Of Contents Subscribe

HVAC TECHNICIAN SHORTAGE

In order to bring more people into the trade and produce more technicians, what should the industry do?
View Results Poll Archive

HVACR INDUSTRY STORE

2015.jpg
2015 National Plumbing & HVAC Estimator

Every plumbing and HVAC estimator can use the cost estimates in this practical manual!

More Products

Clear Seas Research

 

Clear Seas ResearchWith access to over one million professionals and more than 60 industry-specific publications, Clear Seas Research offers relevant insights from those who know your industry best. Let us customize a market research solution that exceeds your marketing goals.

DON'T MISS A THING

Magazine image
 
Register today for complete access to ACHRNews.com. Get full access to the latest features, Extra Edition, and more.

STAY CONNECTED

facebook icontwitter iconyoutube iconLinkedIn i con