a couple of amp.s

[wannafreeze]

I am fond of amp readings.I can`t stop finding questions about them.

Are FLA and RLA the same thing?

To find the proper RLA from LRA, I devide the LRA BY 7 and 6 and 5.and target the 6th.Is there an exact number?

A condensor fan will draw less amp.if cond.is dirty correct?

[R12rules]

Get ahold of the compressor curve for a unit you are working on and you will find a whole new passion for your amp meter.

Copeland's website has them. Do a search on this topic at this site.

[wannafreeze]

Originally posted by altan
I am fond of amp readings.I can`t stop finding questions about them.

Are FLA and RLA the same thing?

To find the proper RLA from LRA, I devide the LRA BY 7 and 6 and 5.and target the 6th.Is there an exact number?

A condensor fan will draw less amp.if cond.is dirty correct?

[rocket]

FLA Full Load Amps
the amp rating of a constant load device, such as fan motor
many years ago was put on some compressors referring to the load at a specific condition
was dropped from compressor UL since compressor is a variable load device, the amps change as the load changes

RLA Rated Load Amps
used for fuse and contactor sizing, as it refers to the maximum amp rating of the compressor
acual running amps varies with the load and is seldom even close to RLA. the cure sheet R12rules refers to is the only way check running amps.
as RLA starts with an "R", many think it means running amps, even though no publication states this. As R12rules states, you may now have a valid use of your amp meter if you obtain a curve sheet. (different for each compressor)

[wannafreeze]

Originally posted by rocket
the amp rating of a constant load device, such as fan motor

well, if I blocked the air flow accross a fan there is no air to push.Less load ,less amp.
also isn`t there a pretty usual proportion between LRA and
running load amp.?Which I see it around 1/6 or definetely between 1/5 - 1/7 .

[rocket]

was talking about a normal running fan motor, blocked air flow doesn't qualify as "variable" load
your 1/6 or 1/7 formula can get you within 10 to 30 %, if that satisfies you , fine

Cope CRN4-0500-PFV rla 34.3 142 LRA
130 cond 45 evap 25.7 amps (142 / 6 = 23.66)
90 cond 45 evap 19.9 amps (142/6 = 23.66
100 cond 20 evap 20 amps (142/6 - 23.66)
110 cond 10 evap 17.7 amps (142/6 = 23.66)

[wannafreeze]

Originally posted by rocket
was talking about a normal running fan motor, blocked air flow doesn't qualify as "variable" load
your 1/6 or 1/7 formula can get you within 10 to 30 %, if that satisfies you , fine

Cope CRN4-0500-PFV rla 34.3 142 LRA
130 cond 45 evap 25.7 amps (142 / 6 = 23.66)
90 cond 45 evap 19.9 amps (142/6 = 23.66
100 cond 20 evap 20 amps (142/6 - 23.66)
110 cond 10 evap 17.7 amps (142/6 = 23.66)

142/5=28.4
142/7=20.28

with these numbers I am
10% high for 25.7 amp
1% high for 19.0 amp
1% high for 20 amp
14% high for 17.7 amp
but you are right I am gonna do more search on this subject.
One thing I don`t understand:
as long as back pressure stays same the load on compressor is the same regardless of the change in head pressure.the numbers you put above must come from the specs.I am a little confused..

[rocket]

Copeland and Carrier provide performance curves on their compressors. Invaluable in trouble shooting and checkng capacity,watts and amps. The examples I gave came from cpCalc, Copeland's program. Knowing what amps you should have gives new meaning to your ampprobe.

Carrier http://www.carlylecompressor.com
download CarWin program

Copeland http://www.emersonclimatecontractor.com
download cpCalc program (need to register)

[wannafreeze]

Originally posted by altan
as long as back pressure stays same the load on compressor is the same regardless of the change in head pressure [/B]

I take this back.when head pressure rises with the same back pressure ,compression ratio thus discharge heat thus amp draw must be going up.