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Thread: A/C compressor amp draw

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    A/C compressor amp draw

    I was wiring up a Relience 6 circuit transfer switch today. Customer wanted the a/c unit to be on the transfer switch. I checked the name plate on the a/c and RLA for the compressor was 14.2.

    However when I pulled amps on the unit it was 6.3. Less than half. It was around 40 degrees out. So the compressor was doing very little work. But I was expecting to see more amp draw.

    How often do a/c compressors draw close to there RLA ratings?

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    Ha. HVAC installation and repair is my main world, but I can't remember the last time I clamped around one that was working....

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    When the conditions are close to the ARI standard test conditions, (95°F outside, 80°F inside) a compressor in good condition will pull close to its rated run-load amps.

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    HVAC Loads

    Quote Originally Posted by Saturn_Europa View Post
    I was wiring up a Relience 6 circuit transfer switch today. Customer wanted the a/c unit to be on the transfer switch. I checked the name plate on the a/c and RLA for the compressor was 14.2.

    However when I pulled amps on the unit it was 6.3. Less than half. It was around 40 degrees out. So the compressor was doing very little work. But I was expecting to see more amp draw.

    How often do a/c compressors draw close to there RLA ratings?
    You are always better sizing for MOCP on HVACR units, especially if they are single phase. If you have starting issues under heavy load conditions, start components are often times a MUST on single phase systems.
    That current will go up under heavy load, and starting current is also an issue.40F outdoor suggests the unit is a heatpump. When in " Heating " mode, AC condensers are performing " Refrigeration " duty load wise. They pull way less current and it also takes less refrigerant to heat than to cool. Your goal is no nuisance trips. If you are just looking at the compressor, you also have the condenser fan however small it may be. Nameplate MOCP is the best.
    Microwave Radiation Dangers should be openly discussed

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    Quote Originally Posted by Saturn_Europa View Post
    I was wiring up a Relience 6 circuit transfer switch today. Customer wanted the a/c unit to be on the transfer switch. I checked the name plate on the a/c and RLA for the compressor was 14.2.

    However when I pulled amps on the unit it was 6.3. Less than half. It was around 40 degrees out. So the compressor was doing very little work. But I was expecting to see more amp draw.

    How often do a/c compressors draw close to there RLA ratings?
    Check same unit on hot summer day when it is loaded harder - then it will draw more amps.

    Whether or not the generator can deliver necessary short time starting current is likely a bigger issue for you than whether it will run the unit.
    I live for today, I'm just a day behind.

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    Quote Originally Posted by kwired View Post
    Whether or not the generator can deliver necessary short time starting current is likely a bigger issue for you than whether it will run the unit.
    OP, check the nameplate for an LRA current value. I suspect the value found will support kwired'd comment above. AC compressors and portable generators can be a crap shoot.

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    Quote Originally Posted by JPinVA View Post
    OP, check the nameplate for an LRA current value. I suspect the value found will support kwired'd comment above. AC compressors and portable generators can be a crap shoot.
    Rated LRA won't necessarily tell you if it will start it or not, it does tell you what to expect if there is infinite amount of current available. Soft starters limit current and motors still start, generator may limit current because of it's impedance yet still have enough output to start it, though it will be kind of like you have a soft starter installed.

    I have a portable generator set I have used during power outage. It will start my heat pump, but it definitely is a kind of "soft start" because of limited output current on the generator pus there can't be much of any other load running or it won't put out enough current to start it.
    I live for today, I'm just a day behind.

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    Quote Originally Posted by kwired View Post
    Rated LRA won't necessarily tell you if it will start it or not, it does tell you what to expect if there is infinite amount of current available. Soft starters limit current and motors still start, generator may limit current because of it's impedance yet still have enough output to start it, though it will be kind of like you have a soft starter installed.

    I have a portable generator set I have used during power outage. It will start my heat pump, but it definitely is a kind of "soft start" because of limited output current on the generator pus there can't be much of any other load running or it won't put out enough current to start it.
    Thanks for the education. The limit of my HVAC knowledge is they can be problem. So I came up with a novel solution when designing my portable generator setup. I wasn't sure if my generator could deliver the current necessary for HVAC; heat pump or AC. My solution was simple and absolute. There are no HVAC circuits through my transfer switch!


    I might get cold...or I might get hot....but my fridge, garage door, TV...and (most importantly) my internet will work.

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    Quote Originally Posted by JPinVA View Post
    Thanks for the education. The limit of my HVAC knowledge is they can be problem. So I came up with a novel solution when designing my portable generator setup. I wasn't sure if my generator could deliver the current necessary for HVAC; heat pump or AC. My solution was simple and absolute. There are no HVAC circuits through my transfer switch!


    I might get cold...or I might get hot....but my fridge, garage door, TV...and (most importantly) my internet will work.
    About 6 months after moving in my house we had ice storm and were without power 3 days. I wasn't prepared for such event yet. I had a generator but it only had 120 volt output, was also a portable welder but only had one 15 amp 120 volt receptacle. We had a wood burning fireplace, but never purchased a blower for it yet at that time. Only place warm was right in front of fireplace. Refrigerator wasn't much of a problem - it was cold and it didn't really need powered. Once the house gets down to around 50 degrees, you will never feel warm, all the thermal mass inside has cooled down significantly when air temp gets near 50.
    I live for today, I'm just a day behind.

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