Could an undersized AC use more power?

[coolguy4]

Hello everyone. With all else being equal (heat load, efficiency rating, setpoint, etc) I am wondering if it is possible for someone to see an increase in electricity usage from an undersized AC unit that runs a lot and has trouble keeping up. Every website on the internet seems to say that an undersized AC will use more electricity than a correctly sized unit since it runs more (or possibly constantly), but this doesn't make sense to me since a correctly sized AC will still run pretty much all day on a hot day and will consume more power while doing so. I'm just talking about single stage units for now.

The way I see it, a smaller AC unit will never result in higher power usage than a correctly sized unit since it is only capable of using so much electricity while it's running, even if it's not keeping up. Looking at it an extreme example, let's say someone has a huge house that requires a 5 ton unit. If someone installed a 5000 BTU window unit, it obviously couldn't keep up and would run constantly. However, with all else being equal, it would still use less power than a 5 ton since it doesn't draw anywhere near as much while it's running and, again, a correctly sized unit will pretty much run all day on a hot day anyways.

So I am wondering if there is any scenario where an undersized AC unit could result in higher power bills? I can't think of one, but if anyone knows of a scenario where it could please let me know. Thanks in advance!

[narkom]

Lets' say that an undersized unit runs 60 minutes in hour and a correctly sized unit runs 40 minutes in hour (ON for 10 minutes and OFF for 5 minutes). The difference in running time is 1/3. So if the undersized unit is more than 1/3 less in capacity its total power consumption will be less.
If it runs 60 minutes in hour and it's undersized for only 20% it will use more power.