From: "Travis Jordan" 
Newsgroups: misc.consumers.house sci.physics alt.home.repair sci.engr.heat-vent-ac
Subject: Re: more fun with air conditioning
Date: Fri, 23 Jul 2004 16:47:33 GMT

J Jensen wrote:
> "Travis Jordan"  wrote in message
> news:...
>> J Jensen wrote:
......
> Thanks for your reply. I especially appreciate the references.

You are welcome.

>>> 3. The a/c uses less current at night ( you measure it with an
>>>    ammeter as it is running ).
>> Depends. Compressor current consumption can vary with the load.
>>
>
> I have always had the opinion that #3 can't be true because it is an
> electric motor and it should take the same amount of current whenever
> it  runs. It should run for a shorter period of time each time it
comes on
> at night, due to the greater efficiency of having cooler outside
> air...  right?

The reason the condenser motors (compressor motor + fan motor) typically
run less at night is because the system load is lighter (less sensible
heat to be removed from inside the home due to reduced heat gain from
the outside).   It is true that the fan motor generally uses the same
amount of current whenever it runs due to it's design and the constant
load of the fan.  In normal operation the compressor motor will draw
somewhere between RLA (rated load amps) and FLA (full load amps)
depending upon the load.