That's because they have smaller compressors for a given tonnage. They've changed the rules regarding A/C efficiency, so manufacturers purposely undersize the compressor. Smaller compressors use less electricity, so, units "appear" to have a greater SEER rating. Yet they are still able to claim full tonnage on the label.
About 20 years ago one major manufactuer tried this idea, and it came back to bite them in the ****. They marketed what they called a "short" 3 ton unit. Not overall height, but capacity. 3 tons is 36,000 BTUH. Their unit had a 32,500 BTUH compressor. A little "short" on capacity. But it undercut everyone else's 3 ton units in price. So, they sold well. Until it got real hot, and the units couldn't cool the house down. But when people complained, the company said it was advertized as a "short" 3 ton. Eventually they were forced to drop the line. But now all manufacturers are doing basically the same thing, and it's legit.
Don't go by what the ad label says, or even the salesperson. Open up the box, retrieve the literature, and check to see what the compressors actual capacity is rated at. 12,000 BTUH is one ton. If the unit says 2 ton, but the compressor is not rated at 24,000 BTUH, it's a short unit.
With all respect to Bonneyman, this response is incomplete and misleading.
All current reputable American HVAC vendors rate their equipment according to ARI standards. Among other requirements, this calls for an indoor condition of 80/67 db/wb, with an outdoor temperature (for the condensing unit) of 95 db. In order to allow an 'apples to apples' comparison, all equipment specifications include this performance parameter. (In this case, I would also recommend that
energy usage comparisons be done by the EER rating and not the SEER.)
Due to a variety of factors, equipment tested under these standards, say for a
nominal 3 ton AC unit, may result in a total cooling output (sensible and latent) of anywhere from roughly 33,000 to 37,000 btuh. This information is freely available and does not constitute fraud or deception on the part of the manufacturer. This is the case throughout the industry. And just as the equipment varies according to actual output, so does the electrical requirements, the physical size, operating efficiencies, features, etc.
What
is important is that the selected equipment
meets the calculated requirements for the intended purpose. For some specific applications one vendor's equipment may be more desirable than another. An informed decision by an experienced designer or engineer will result in the proper equipment selection.
What is equally important, if not even more so, is that for most applications the interior conditions will more likely be 74-76 degrees db, not the 80 degrees used for performance testing. And as for outdoor temperatures, many projects will require a higher, or sometimes lower, outdoor temperature. Again, here is where the professional will have an advantage over the lay person.
For home garages, maybe this isn't so very important. I suspect that just getting in the ball park will be satisfactory for most weekend mechanics. But for your main residence, or a commercial or institutional project, getting it right means the difference between a successful installation and a possible career-ending mistake.
As to manufacturers taking a little liberty with published performance data, I am aware of one commercial manufacturer that was caught doing this in the 1990's. It was a disaster for the manufacturer, the design engineers, Mechanical Contractors and the property owners who got suckered. The lawyers made out quite well I imagine.
Just wanted to add some perspective. Perform a proper load calculation, and select the appropriate equipment.
as always, offered only as opinion
