How to calculate the capacity for the unit using LRA

That makes no sense. LRA is going to be for a motor or compressor. I've never heard of a 20562 BTU machine. You have to read the data plate on the machine, either indoor or outdoor unit will tell you. If you can't read the data plate turn the power off and look at the data plate on the actual motor itself. Good Luck!!

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LRA is locked rotor amps. Likely referring to your compressor. If i had to guess i would say 1.5 ton because 42 is not much. You mostly need model number to determine capacity.

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LRA on the data tag stands for "locked rotor amps" and has nothing to do with tonnage. In the model # there should be a number to use. And divide that # by 12 (12,000 btu/ton). So if I had a PFG24H200 it would be the "24"and a 2 ton unit

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Use a clamp on ammeter to check the LRA (locked rotor amperage) at the moment the compressor is energized. It should not exceed the rated LRA printed on the data plate. If it does then ohm the compressor for a ground or short between windings

The Old Rule of Thumb is 400 square feet per ton, but you really need to do a heat load calculation to be safe. A lot of windows on the west or south side of the house will really increase your load and you may need a lot larger unit. Insulation also changes your load so you may be able to cool a larger area. You may be able to get the Heat Load Calculation Form either online or from Johnstone supply. They are on the internet.

The most important spec that you will need is the LRA rating. What this stands for is locked rotor amps. The LRA rating is what the AC unit will draw from the inverter while the compressor starts up. This is a very important spec when sizing an inverter for use with an AC unit. After you get this spec you will multiply it by the voltage and this will be the startup wattage needed by the inverter.

For example if your LRA is 60.6 amps if you multiply this by 115 you will get roughly 7000 watts at start-up.
The next thing to take into consideration for a AC unit is battery bank size. Your next step in setting up a system for use with an AC unit is finding a sufficient recharge source for the batteries. You will want to have a minimum of a 150 amp alternator to recharge a system with a small AC. I do not know whether you will be able o accommodate them.
Why don't you go for solar power as standby OR a small generator????????

One really has not much to do with the other directly



BTU - British Thermal Unit.- A heat measuring unit. IE:12,000 BTU (British Thermal Unit.) The amount of heat required to melt one ton of ice.


LRA - Lock Rotor Ampere-LRA is nothing but locked rotor current , generally it is located on compressors name plate, when ever pistons locked at a particular position the rotor does not move further at the time rotor draws large current, that current is located on name plate, by seeing that LRA we can know compressor rotor was locked

Two or three remarks: The Gallon is a unit of capacity (volume for fluids). So it cannot be converted into centimeters. In cubic centimeters yes, but not centimeters.
In addition to that there are two volume capacity units called gallons: the US gallon, and the imperial gallon. 1US gallon=3.7854 liters and 1 Imp. gallon=4.5460 liters.

To do your conversion use the facts that 1L =1000 mL=1000 cm³.
1 gal = 3785.4 cm³ or 4546 cm³.

LRA is Lock rotor amps.
It is according to compressor capacity.