Aircon Question

[i am bob]

Hey Bruce...or anyone else,

 

I have a digital meter from the power company at my house here.  When I turn on the LG aircon it goes to about 1.41 Kwh on low fan.  When I put it on hi fan it DROPS down to 1.38Kwh.   HUH What Really??????  Is the aircon using LESS electricity on high fan?  Is it more efficient or is the meter lying to me?

 

Ah grasshoper... there is an answer to what you seek...... But before I saying anything wrong..... I will let BOB take this one and explain the nuances of RLA as opposed to FLA and work loads and how this effects the amp draw / kilowatt useage.... 

Ah, c'mon Bruce...   You and I both know we are looking at RLA and LRA rather than FLA for a possible answer to this one.  Stop being so sneaky!  RLA is Rated Load Amperes which is when the motor is actually working normally.  It is mistaken as to being THE maximum value while it is actually a quantative figure.  LRA is Locked Rotor Amperes - or the power spike associate with the initial push to get the motor to turn...  We all know it takes much more power to start a motor than it does to keep one running.  This kind of blends into the RLA as the motor goes to work at normal speed.  And FLA is Full Load Amperes which really is what the power rating is when doing the good old smoke test!  All FLA is is the maximum amount of power the motor can take before it goes poof! The fun stuff!  A lot of people confuse that with the actual RLA at max work load.  In fact, FLA is the amperage used when the motor is at Full Rated Horsepower of the motor under designed load. The nice thing about FLA is not having to worry about it.  Unless the engineer designed your ac unit to self destruct, that is.  Nothing is designed to operate normally under the true FLA - even though the manufacturers insist on listing on all their motors. It is probably the most misunderstood and wrongly taught part of this technology.  Now the question is... What did Steve see?  Would you believe something totally different?  LG AC units have what they call their Inverter something-or-other technology - I don't remember the exact name because it's been a while.  But what this technology does is control the compressor speed in relation to the cooling.  As it will cool more efficiently when the fan is on high, the compressor can cut back on it's speed.  When the switch is put to Low, the compressor has to speed up.  Now we know from what I wrote above that a motor under load consumes more power.  The problem is that it takes more power to increase the speed of the compressor than it does the fan - it's a harder load to achieve.  And, just for a little more information on LG's motors - both the fan and compressor are using brushless DC motors that require only a little more power when under load but can maintain that level constantly and consistently while using less power overall for this application.  How am I doing Bruce?  I really am much better describing electronics since my background is in Avionics Technologies (Aerospace Electronics) and backing into the Electrical (lights, motors, starters, etc) as a secondary. 

 

I guess that means it's your round for the coffee...   :thumbsup:

[Bruce]

How am I doing Bruce?

 

Well not too bad.... but the FLA info was lacking the Service Factor rating. Which years ago was 1.5 at least, then slowly they dropped it back to actual plate rating! (Damn Chinese!) You were touching on the subject without actually naming it. 

 

On a side note.... one of the more tricky issues in condensor fan replacement for the 'parts changers' is all they look at is HP rating and not speed (1075 or the more modern 875) and simply change the motor to the same HP rating. that new motor may be the same HP but the wrong speed. So it burns out and so does every replacement after that. Until I or Bob come along... the LAST thing I do after changing the fan motor is check the running load amp (RLA) of that motor to see if it is higher then the rating on the motor. If it is... you are doomed for a premature failure. Years ago it did not matter as the Service Factor of 1.5 meant that the rateing on the label may say 2.7 amps but it can 'take' 50% higher before a failure. But not today. 2.7 amps means just that and not 2.8. On average the correct motor will pull less than the rated amps on the lable if all is sized properly.  

 

And then there is the Work Load.... basically for a fan motor at any rated speed, it moves x amount of FREE AIR. But any restrictions in front of the air flow or behind the blades (incoming air) LESSENS the load. So the AMP draw LOWERS.  

 

The ac blower can move X amount of air out in the open, but that same blower when installed in anh AC unit has to SUCK the air through a coil, which is a restriction and that LOWERS the amp draw.  

 

A unit set on LOW FAN may pull X amps (fan load) as it is moving the max air (for that speed) through the restricting evaporator coil at a certain rate. But when you switch to HIGH, the fan also may pull slightly less AMPS as the fan is able to move more air than it can get through the evap coil.

 

NOTE.... the Air Handlers of years ago often PUSHED the air up and through the coils which is less efficent than SUCKING the air through the coil. So the older central ac units had fan on bottom, coil on top and now, the reverse is true.

[i am bob]

Sorry Bruce - I didn't go into the work involved on air flow as some ac units don't change - poor design usually.  I knew about that feature on the LGs with the compressor and that does make a big difference in power draw.

 

FLA was changed so many years ago that I didn't want to confuse anyone reading this either.  It went from a Service Factor value where you knew you had the right motor to become smoke tests to see if your neighbours were watching.  So anything approaching FLA is pretty well useless these days.  

 

It looks like we do the same thing.  No matter what I am working on, I always check the RLA after everything is up and running properly.  Breathing smoke kind of sucks - even if that smoke is a cool smoke at first..  They don't make menthol motors.

 

:mocking:

[Thomas]

Ah, c'mon Bruce...   You and I both know we are looking at RLA and LRA rather than FLA for a possible answer to this one.

Oh! I thought it was NPA  :)

[Bruce]

It looks like we do the same thing. No matter what I am working on, I always check the RLA after everything is up and running properly. Breathing smoke kind of sucks - even if that smoke is a cool smoke at first.. They don't make menthol motors.

 

The difference between a 'parts changer' and a mechanic....... In south Florida I have to compete with a huge 3rd world influx of people including maintenance men and doo it yourselfers who came to America and will work for $50 a day. No license, no insurance and no real understanding of how things work. It is great in Cuba where they have learned to adapt and improvise as needed to keep things running. But that same mentality is not so good in the US where the proper parts are available.

[i am bob]

Ah, c'mon Bruce...   You and I both know we are looking at RLA and LRA rather than FLA for a possible answer to this one.

Oh! I thought it was NPA   :)

 

 

What's this?  This NPA in FLA?  Florida?  Bruce, did you become a member yet?

 

:mocking:

[Bruce]

 

Ah, c'mon Bruce...   You and I both know we are looking at RLA and LRA rather than FLA for a possible answer to this one.

Oh! I thought it was NPA   :)

 

 

What's this?  This NPA in FLA?  Florida?  Bruce, did you become a member yet?

 

:mocking:

 

Well starting a chapter was easy... but just try to get any dues from those guys...... :hystery:

[MikeB]

I've had my 1HP Carrier going on 2 years. For the past couple months it's been shutting down with an F something status. I figured out it was happening because the front coils were icing because they were clogged with dirt and debris. Today I took it outside and sprayed and cleaned it with a hose and brush. There was a lot of grey-brown slime and sludge on the inside bottom, pretty gross when you consider you're breathing the output. It runs MUCH better now, like new really. The compressor actually starts and stops as needed, before it was running all the time and still not keeping up. Some of the components looked like they were burned, probably because it was overheating due to dirt buildup.   

It turns out my diy job wasn't so good. Although I cleaned the clogged up coils that was causing the shutdown, I inadvertently pushed some of the dirt into the natural path of the water draining to the back of the unit so gravity was foiled and I had water leaking heavily from the front. An aircon tech came and cleared that then took everything apart and cleaned it with high pressure water and air. Still an amazing amount of dirt and mold. Lesson learned: unless you know what you're doing, pay someone who does.  

[Bruce]

I've had my 1HP Carrier going on 2 years. For the past couple months it's been shutting down with an F something status. I figured out it was happening because the front coils were icing because they were clogged with dirt and debris. Today I took it outside and sprayed and cleaned it with a hose and brush. There was a lot of grey-brown slime and sludge on the inside bottom, pretty gross when you consider you're breathing the output. It runs MUCH better now, like new really. The compressor actually starts and stops as needed, before it was running all the time and still not keeping up. Some of the components looked like they were burned, probably because it was overheating due to dirt buildup.   

It turns out my diy job wasn't so good. Although I cleaned the clogged up coils that was causing the shutdown, I inadvertently pushed some of the dirt into the natural path of the water draining to the back of the unit so gravity was foiled and I had water leaking heavily from the front. An aircon tech came and cleared that then took everything apart and cleaned it with high pressure water and air. Still an amazing amount of dirt and mold. Lesson learned: unless you know what you're doing, pay someone who does.  

 

Using water and maybe air to clean is a much better option than using harsh chemicals. In the US it is very popular to use the chemicals and most (not all) produce a foam which helps to push out the dirt... at the cost of eating the metal. Not metal you can see so much but the metal to metal surface where the copper tubing meets the aluminum fins. Once you have poor metal to metal contact, no matter how clean your coil looks, you have issues now that cannot be fixed without replacing the coil.

[Mike S]

Bruce I'm sure you know there is an acid based and an alkaline based coil cleaner ..... in the hospitals we weren't allowed to use the acid for a number of reasons ..... but the alkaline worked great .... years ago the sailesman that sold it to me convinced me by actually cleaning a unit we had already cleaned and then she took some and put it behind her ear to show it wouldn't eat the aluminum fins ..... I was impressed ..... (but I was more impressed when she bent over in her short dress and cleaned the coils) .......  :mocking: :mocking: :mocking: :cheersty: