Replacement window air conditioner is weak

A 14 year old Sharp window air conditioner rated at 10,000 BTU/hr was recently replaced with a much more efficient 12,000 new Sharp window unit. The replacement was motivated by the higher energy efficiently, and my desire to get a bit more cooling.
The replacement unit does not deliver nearly as much cooling as the original, despite being brand new and having 20% higher rated BTU/hr output.
It does ultimately achieve adequate cooling, but with much longer compressor cycles, and thus higher operating costs.
Is there any objective measurement I can perform to demonstrate that this unit is not putting out anywhere near its rated capacity? I cannot find any published data to evaluate delta T, discharge air temperature, or other quantitative evidence. I ultimately have to convince the service people that this unit is defective.
Many thanks for any suggestions.
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Have you verified higher operating costs? I mean, have you had a bill yet? My experience says longer cycles are desirable, as it dehumidifies better, often making it quite comfortable at higher temperatures. .
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Perhaps the higher efficiency is achieved by using a smaller compressor that runs longer cycles? Unless you know the operating (not peak) amperage of both compressors I don't see how you can conclude that the operating costs will be higher...
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wrote:

Thanks for replying. To answer both your question as well as the similar comments of "Larry the Snake Guy":
Both the old 10,000 BTU/hr and the new 12,000 BTU/hr air conditioner draw nearly the same current when running at maximum fan speed and with compressor engaged, about 9.6 amps. The older unit was a 10,000 BTU/hr unit, and the new unit is rated at 12,000 BTU/hr. The higher energy efficiency rating of the new unit (Energy Star / 10.8) accounts for the fact that it (supposedly) can produce 20% more BTU/hr despite drawing the same current as the older, less powerful unit.
The difference in cooling capacity is quite noticeable, but unfortunately in exactly the opposite direction from what I intended:
I get less than a 1.5 degree temperature drop per hour with the new unit. With an 85 degree outdoor temperature, it will now take roughly 8 hours to pull the room temperature down to the low to mid 70's.
With the older unit, I easily got well over 2.0 degree drop per hour, maybe even 2.5. On an 85 degree day, the same room was cooled in well below 4 hours, maybe closer to 3 hours to a 75 degree temperature.
It doesn't take an electric bill or a PhD in thermodynamics to see that the newer unit is cooling far less quickly, and is drawing nearly identical amperage (at the same line voltage of about 116 VAC) when compared to the older unit.
I never measured discharge air temperature on the old unit, but the new unit puts out cool air whereas the older unit put out truly cold air. I can easily measure the temperature of the cooled air which the new unit discharges if that would be useful. The discharge air velocity of the new unit seems roughly the same as the older unit, both of which are operated at their maximum (High) blower speeds.
So I am back to my original question as to how to measure whether this new unit is working correctly.
If I had not owned the prior unit, same manufacturer, 20% lower BTU/hr rating for the last 14 years and grown very accustomed to its performance, I would not have any complaints about the new unit, since it does cool. It just takes a lot longer, puts out noticeably less cold air, and draws as much power as the prior unit but for nearly double the length of compressor cycles.
If anything, one should expect that a higher output unit would have shorter compressor cycles, all other things being equal. The new unit compressor runs easily twice as long as the older one did to achieve similar cooling.
I am concerned that not only do I suffer the increased energy cost as well as the increased noise now, since the compressor is running nearly constantly, but also the fact that as we get further into the summer season and outdoor temperatures rise to 95 or perhaps higher that this new unit will not have the ability to achieve greater temperature drops, since the compressor cycle now is nearly 100% with outdoor temps closer to low to mid 80's.
Again, I welcome suggestions, and thank you in advance for your help and advice.
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What is the room temp and output temp of both units, maybe the new one is low on freon? If you just bought it maybe there is an open floor model at the store?
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With that info, I'd say take it back
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wrote:

I wish I could. My problem in taking it back is that the unit took two of us to install it and carry it up a long flight of stairs, and at a bit over 80 pounds is not easily removed, combined with the fact that additional holes needed to be drilled into the mounting flange in order to properly fasten it to the surrounding window frame / sash.
I want to have their in-home repair person come out and have him, at the expense of the manufacturer, either repair or replace the unit, since the warranty does provide for in home service and either repair or replacement if the unit is defective.
Proving the defect is what my question has been all about. Yet I have yet to hear even the slightest suggestion as to how to do so.
As I originally stated in my first post yesterday:
"Is there any objective measurement I can perform to demonstrate that this unit is not putting out anywhere near its rated capacity? I cannot find any published data to evaluate delta T, discharge air temperature, or other quantitative evidence. I ultimately have to convince the service people that this unit is defective."
Regarding the comments I have received that lower humidity = greater comfort = longer compressor cycles, etc., all of what you say is indeed true, but is not the explanation for my problem.
This unit has no ability to either measure or apply this psychrometry. It purely and entirely cycles on temperature, not humidity. It behaves exactly as if it had low cooling capacity, perhaps as a result of improper refrigerant charge, faulty compressor valve, weak air flow, etc. The compressor runs continuously, the unit draws 9.6 amps continuously, the room does not get especially cool, and the energy consumption and lack of cooling / delta T is very simple proof of what I am describing as a "weak" unit.
I am looking for a way to measure its true capacity, and confirm that it is defective.
If this were an "A" coil sitting in my furnace plenum, I could instrument the air flow and also the temperature drop across the coil, and the combination of the two combined with the static pressure would allow an accurate statement of the efficiency / correct functioning of the unit. Unfortunately I have no such access in a window unit.
Any other ideas or suggestions would be sincerely appreciated.
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Smarty wrote:

Okay, the first test a technician will attempt is a temperature differential measurement.
The temperature output of an A/C unit should be at least 10 less than the temperature of the input air.
If your old unit was generating a 12 difference and your new machine only 8, there's your problem.
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HeyBub wrote:

If the new unit pushes half again as much air through it than the old one did, it would perform the same as the old one, given your criteria.
Jon
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Thanks all for excellent suggestions. I can't get a probe to the outside surface of the coil to measure delta T, but the other approach sounds especially tempting, all considered.
Again, thanks for the guidance.
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Smarty wrote:

You don't need to get a probe anywhere. Put a thermometer in the outgoing air vent. Record the value.
Stick the thermometer in the vent that pulls in the room air. Record the value.
The difference between the two should be ten degrees or more, irrespective of air volume.
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Maybe I'm misunderstanding what YOU are saying, but I think the part you're missing is that everyone is talking about the delta T between the input air (being sucked in the bottom section of the AC) and the output air (being blown out the top). Both of these are acessable from inside the room and what's going on in the outside half of the AC isn't terribly inportant for what you're trying to find.
And just to thorough since I didn't see you mention it, are you saying you used a meter to measure the current as each AC was running? You're not going by the ratings listed on the fan and compressor, I assume?
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That was not mention in the original post was it?

If the unit is defective, they will. If it is not defective, expect to pay for a service call. Of course, you may or may not get a competant service guy. Get some data first.

Have you asked the service people for that information? Have you explained the situation?

You'd need considerable instrumentation to extrapolate "true capacity"

Why not? All you need is a simple probe thermometer to determine temperature drop.

Once you've determined temperature drop, call the company with the information and they should be able to tell you if it is performing within some sensible tolerance.
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Without going into detail, there are various ways that you could ensure the unit will be defective when it is examined by the service technician.
--
There is always an easy solution to every human problem -- neat,
plausible, and wrong." (H L Mencken)
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On Jun 30, 1:09pm, snipped-for-privacy@sdf.lNoOnSePsAtMar.org (Larry W) wrote:

I had a job once long ago, where part of my responsibility was returning defective auto parts for credit. I had a batch of starters rejected, & while they would turn & run, they wouldn't start cars. We were out the postage for sending them once, & my boss was annoyed. I guaranteed him it would never happen again. From that time on, before we sent them in, I hooked each one to an old Lincoln 225 welder before shipment. They would rock and roll for a few seconds, then a puff of smoke would roll out. I never had one rejected again the whole time I worked there.
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Eric in North TX wrote: <text smoked>

Some IT guys do the same regarding "proper termination" of computer equipment:
http://www.fiftythree.org/etherkiller /
"Now localtalk is really local."
--
PB
"I suspect you\'re an arrogant little pissant who grew up in the
Red Bull generation." - CJW
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Longer operating time does not equal higher cost. What is the power draw of the new compressor versus the old? I know that one unit I replaced was about 50% of an older model, thus big savings. Longer times often means less temperature fluctuation and better hubidity control.
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    Exactly. In general the longer the running time the more efficient and comfortable. Short run times tend to accompany less efficiency and poor humidity control.
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Smarty wrote:

So far everything you've posted on this thread makes sense to me.
As to how to "prove" something's wrong....
If I absatively HAD to do it, which I trust I never will....
.
.
.
You could start with this basic equation good for most of the air near ground level on our planet:
BTU/Hr = 1.08 x CFM x delta T
And, maybe build out some sort of taped together corrugated cardboard duct (a couple of feet long) from the cold air outlet, and assuming you've got access to an air flow meter, try and get a fair idea of the average velocity of the exiting air.
Multiplying that air flow in feet per minute (60 times feet per second) by the area of that duct in square feet should give you a pretty good idea of the CFM.
The delta T between input and output is a cinch to measure, so there you've got all the factors close enough for gummint work, excluding humidity of course.
Sounds like a good Science Fair project, huh?
Frankly, I think I'd go with that 5 degree delta T being unreasonably low for a window A/C unit and start leaning on the place you bought the beast from to let you try another one ior take it back.
Good luck to you and the Red Sox,
Jeff (In Red Sox Nation)
--
Jeffry Wisnia
(W1BSV + Brass Rat \'57 EE)
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