amping out hermetic compressor with clamp ampmeter

robert norton

what is the correct way to amp a hermetic compressor i have a clamp style amp meter and was wondering with leg shoul i just ck run leg of compressor for rla on compressor plate

D lux_2

the

common leg not the start or the leg off the cap.

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

Dale

Either of the feeds

Both of the feed wires should give you the same result. If the feeds go directly to the contactor it doesn't matter which one you pick. If you see a RLA this means "Rated Load Amps" ( not running load amps) and comes from the MCC or manufacturers continous current the point at which the overload protector will trip. The MCC is divided by up to 1.56 or usually 1.4 to get the RLA. The RLA is used to size the wiring and fused. It is a good idea to clip the compressor to check amps but you should never see anywhere near the RLA. If the compressor is good cooling load affected by charge varies the amps seen. I often fuse RLA 25 units with 15 amp slow blow fuses and have no trips. The running amps on a 90 degree day will be about 8 for a 2 ton system. Amps show how much work the compressor is doing and is one of although IMO not the most important diagnostic tool. I like to see a tech check this at startup as a big difference will be an indication that something is out of spec.

robert norton

my question is by using a feed you would also be picking up the amp on the condenser fan i knew you can check the whole condensing unit that way but if i question just the compressor couldnt i amp either the start,run or common on the compressor for the compressor only amp readings

Dale

True

Yes you do get whatever the condenser fan and also the crankcase heater in some applications when you clip the feeds. If you want to be sure you're getting only the compressor actual run amps clip the lead to common or the lead to the run terminal, the current going through the cap is real and what's going through the start winding although it is a bit out of phase with the run.