Air Conditioning, Ambient Temperature and RLA Effect

Richard Thacker · 03-08-2009, 06:52 AM

Gentlemen I have a question that I would like explained, if possible, by someone with some knowledge of motors.This occurred last year...

Example: 3.5 ton system / with a listed R.L.A. of 18.4 Amps / Outdoor temp is 91*F / Return air is 74*F / Supply air 58*F / Actual observed R.L.A 18.1amps / unit is 2 years old

I called for the system to be further evaluated by an HVAC Specialist because the RLA seemed to running to high and may be a sign of motor concern. The answer I recieved from the contractor who installed the unit was " The system is running normal and there is not a problem with amp draw. The higher amp draw is due to very high outdoor temperatures making the unit have to work harder."

Now I don't know a lot about motors, but I can not see how a system that under normal conditions would be running +/- 11.5 amps would need that much more power for a day that was only 91*F. What I would like to know, and explain it in simple terms:

1. Is the HVAC contractor correct?
2. If he is correct when did 91*F become "very high outdoor temperatures" and why would it cause such a high jump in the RLA?

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**Michael Thomas** · 03-08-2009, 07:58 AM

Perhaps you have an HVAC background, but IMO that's well beyond the every HI SOP I'm aware of, and likely to land you in hot water.

**Jerry Peck** · 03-08-2009, 12:22 PM

Richard,

Try this this: RLA verses FLA - HVAC-Talk: Heating, Air & Refrigeration Discussion

A.D. Miller · 03-08-2009, 02:21 PM

Originally Posted by Jerry Peck

Richard,

Try this this: RLA verses FLA - HVAC-Talk: Heating, Air & Refrigeration Discussion

JP: I just read that thread and now can safely report to you that I know less about the matter than before.

Richard Thacker · 03-08-2009, 05:13 PM

Jerry, thank you. That did explain a great deal...I think.

Denny L West · 03-09-2009, 04:37 AM

Did you get that answer in writting from the contractor . cause that will defuinatly clear you on that . and If Your Not Lisc. HAVC that is out of the scope of a home inspection. sometimes its better to say its not my area of expertise and recommend a HAVC contractor to evaluate then its up to the client to except or not .

Richard Thacker · 03-09-2009, 05:06 AM

Gentlemen I have a question that I would like explained, if possible, by someone with some knowledge of motors.This occurred last year...

Example: 3.5 ton system / with a listed R.L.A. of 18.4 Amps / Outdoor temp is 91*F / Return air is 74*F / Supply air 58*F / Actual observed R.L.A 18.1amps / unit is 2 years old

Correction: The actual supply Temp at the time was 68*F

I Don't know if data would have made a difference, but is still a concern on its own merits.

Richard Stanley · 03-09-2009, 07:47 AM

only 6 degree delta -- needs service.

Richard Thacker · 03-09-2009, 12:58 PM

So as I see it RLA only becomes relevant when it exceeds the manufacturers listed maximum limit and amp draw should not be used as a standard for measuring a motors condition.

**Jerry Peck** · 03-09-2009, 03:25 PM

Originally Posted by Richard Thacker

So as I see it RLA only becomes relevant when it exceeds the manufacturers listed maximum limit and amp draw should not be used as a standard for measuring a motors condition.

That's a good way to put it.

Now, for a knowledgeable HVAC guy who is also checking many other things and putting them all together to arrive at some 'Yep, it's about a goner' or 'Nah, it's okay for now' decision, that's way beyond my knowledge with air conditioning.