Air conditioner test question

I came across a website that said a test for whether your a/c is working properly is if the air coming out of your register is 15 or more degrees cooler than the outside air T (going into the a/c). Is that a good criterion?
thanks
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No
The temperature oudside has nothing to do with what you keep the indoor temperature. Normally the temperature should be between 16 to 20 degrees colder at the supply register than at the return grille. But that depends on indoor humidity, return temperature and air flow. Many service techs can't do capacity and efficiency testing, I doubt that you can.
I do it for our local utility on occasion. It takes several hours and I use about six thousand dollars worth of test equipment.
Stretch
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This is Turtle
From 15F to 20F is the range but i like closer to 20F if possible. now this is only a real little look at the ability of a hvac system and can be running poorly and still get these numbers.
TURTLE
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Jim-Poncin wrote:

--
Crank Your Air-Conditioner Up To Specs
http://www.udarrell.com/air-conditioner-capacity-seer.html
  Click to see the full signature.
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