In the HVAC industry, RLA stands for Rated Load Amps. It represents the maximum current a compressor should draw under its most demanding design conditions. Many people mistakenly call it “Running Load Amps,” but this is a critical distinction: your compressor should rarely actually pull its full RLA. Instead, the RLA is a mathematical benchmark used by manufacturers to determine wire sizing, fuse ratings, and safety limits.
Understanding the relationship between your system’s Actual Amp Draw and its Rated RLA is the fastest way to diagnose a struggling unit. If your compressor is pulling close to its RLA on a cool day, it may indicate a dirty condenser coil, a failing capacitor, or a refrigerant overcharge. Conversely, if the amperage is significantly lower than expected, you might be looking at a low refrigerant charge or a failing internal valve. To truly troubleshoot a system, you must look at the RLA not as a goal, but as a ceiling for safe operation.
To see if your compressor’s current draw is within a healthy range, use the Compressor Amperage & Health Auditor below.
What does RLA mean in HVAC
RLA stands for Rated Load Amps in any HVAC system. It can be defined as the rate of the cooling capacity of the system while it is running or operating its functionalities. These ratings are composed by the manufacturer and may vary a bit from brand to brand.
On average, the compressor or condenser of almost all kinds of HVAC systems or air conditioners requires about 5 to 6 RLA (Rate Load Amps) for a cooling capacity of one ton.
What is RLA on a compressor
RLA on a compressor is the maximum amount of current that can be drawn while working in any kind of condition.
Do keep this fact in mind that RLA stands for Rate Load Amps as some people confuse it with Running Load Amps. This confusion makes them believe in an incorrect concept that a compressor should always draw these huge amps.
But the reality is that RLA is the maximum point while there are possibilities that your systems may only draw less or maybe half of it.
How to check the RLA on the compressor
Most of the HVAC manufacturers now label RLA or amperage rating right on the compressor in the form of a metal plate or paper sticker but technicians prefer to find the exact correct value on their own for better results.
Apart from this, the internet has provided a great deal of convenience as you can simply search the brand name with the model number of your HVAC system. This will bring you all the information in almost no time and you can take what is required.
Do keep this fact in mind that RLA alone cannot define whether the compressor is working perfectly or needs some repair or maintenance. Taking the services of a professional is always the best option unless you have years of knowledge as well as experience about the compressors working in the HVAC systems.
💡 Pro Diagnostic Tip: When a compressor consistently exceeds its RLA, the internal thermal overload will trip to prevent a fire. This usually results in the outdoor fan running while the compressor remains silent. If your unit has stopped cooling and is displaying a sequence of lights, use our HVAC Error Code Index to see if a high-amperage lockout has occurred.
How to calculate RLA on a compressor
- Finding RLA is the process of solving a simple equation as you only need two values to get your required amperage rating.
- You can start by doing various tests to get the value of MCC (Maximum Continuous Amps) just before the overload on HVAC trips.
- Once you have determined the perfect value of MCC, simply divide it by 1.56 as this is the way highly recommended by ULI (Underwriters Laboratories Inc.).
- Although it is a standard value set to determine the RLA, some manufacturers use 1.44 as a dividend for their system. One such compressor manufacturer is Copeland.
How do you calculate RLA from LRA
It is more than simple as many technicians have followed this way of calculating RLA from LRA. This is a common mathematical term in which you just divide the value of LRA by a number ranging from 5 to 8. The exact number can vary due to various kinds of HVAC systems and their functioning properties but the range remains the same.
Talking about the LRA, it stands for Locked Rotor Amps which is the maximum amount of current that may be fetched at the time of system startup. It only occurs for a few seconds and comes down right after the system starts running properly.
You can calculate RLA just by the equation; RLA = LRA / 6. Where most people suggest this value as it is the average of the range, some manufacturers recommend dividing it by 5.56 to get more accurate RLA values.
Compressor RLA to kW
There are a few values that are required to convert LRA to kW in the most accurate manner. You need values of RLA, voltage, and fan motor amps. Suppose the value of RLA is 22.4 amps, fan motor amps are 1.7, and volts are 460. So, the kW will be derived as:
- RLA x 2
- 22.4 x 2 = 44.8 amps
- (RLA x 2) + Fan Motor Amps
- 44.8 amps + 1.7 amps = 46.6 amps (Add 1.7 more for every fan even if there are more than one).
- Square Root 3 of (46.6 amps x Volts)
- Square Root 3 of (46.6 amps x 460) = 37kVA
- Now multiply the efficacy power factor, such as if it is 80%, the value of kW will be as:
- kW = 37 x 80%
- kW = 29.6 or 30 kW.
💡 Pro Diagnostic Tip: Amperage is directly tied to the work being done by the refrigerant. A high suction pressure—and therefore a high VSAT (Vapor Saturation Temperature)—will naturally cause the RLA to climb as the compressor works harder to move the denser gas. Always check your saturation temperatures before condemning a compressor for high amps.
Are RLA and FLA the same
RLA and FLA are considered the same as they both are the amount of current that is drawn by the HVAC system while operating. The only difference is the type of condition in which the compressor is operating.
RLA vs FLA
| RLA | FLA |
| Stands for Rated Load Amps. | Stands for Full Load Amps. |
| Maximum current drawn by an HVAC system’s compressor. | Amount of current drawn during some specific operation or condition of the compressor. |
| Remain intact in all kinds of operating conditions. It can be said that RLA is the current drawn during the normal working of a compressor. | Only come into action when the compressor or motor has reached full load horsepower or torque. |
RLA vs LRA
| RLA | LRA |
| Stands for Rated Load Amps. | Stands for Locked Rotor Amps. |
| Maximum current drawn by an HVAC system’s compressor. | Amount of current that is drawn during the start-up of an HVAC system’s compressor. |
| It applies no matter what kind of conditions the compressor is working in. | Only applies at start-up while you provide full voltage. |
| Remains during the whole operating process or running time. | Stop just after the compressor has started working. |
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