is it better to keep my home air/conditioning unit in the "ON" position intsead auto?

I would agree with everything that Rob said but if you do have the proper amount of supply vents and proper return vent size, your dampers are open, your filters are clean, and your vents aren't blocked....then you possible may need better insulation in your attic or crawl space between your roof and ceiling. What will also help is if you place your sensor for your thermostat in the return air to get an average of your homes' temperature. Having good insulating upstairs would be a key factor though.

*When it comes to auto or on, this function is just for your "indoor blower" (circulating the air in your house) operation.

Auto ~ meaning that the "indoor blower" will only start when there is a need for cooling.

On ~ meaning that the "indoor blower" will start and continue to run regardless of if there is a need for cooling or not.

COST: yes, it will cost more because you are running your compress/condenser fan/blower all of the time. Until you can get your problem resolved, I would suggest that on cooler breezy days to open your windows to have a draft blow through your house with your system OFF of course. You can also set schedules on your thermostat...depending on the model you have. For the time that your away, it will turn off and when your home, it will turn back on (check your thermostat manual). Or you could just shut it off before you leave and turn it on when you get home.....saving money.

Wear and Tear: Yes, in a sense it will wear on your compressor and other components but these things are built to last for years. You probably will have to change filters and clean the coils more often though. But all of this is only until you get the problem resolved.

It seems like there is a problem with your air conditioning. If you have central air there should be a return air vent on the top floor along with supply vents under or above each window. Check the supply registers to make sure they are in the open position and check your return air. There can sometimes be a filter on the return air. Check that to make sure it isn't clogged with dirt. The return air should be about 24" by 12" ish and be in the hall either on the wall or on the ceiling. If the registers are closed no cold air is making it to the top floor. If the return air is clogged the air pressure will keep any cold air from making it to the top floor. If the system was installed after the house was built you may need to trim the bottom of the doors to allow air to flow from the rooms to the hall and into the return air duct. there should be about an inch of clearance.

Upstairs is always going to be hotter. Heat rises. If you leave it on all of time your electric bill will be higher. When in the auto position it turns off when it reaches the desired temp. You can move your thermostat closer to the stairs but it will still always be hotter on the 2nd floor unless you had a 2nd system installed. Make sure you change the filter on a regular basis.

The sun is beating down on the roof heating the second level. You need more insulation in the crawl space between the roof and the ceiling. Insulation is not just for cold climates. It helps keep the cold air outside in winter as well as hot air in summer. It'll keep more of the ac cool air inside and not let it escape.

How to save energy on appliances.

http://www.ezfix101.com/2011/12/energy-saving-tips...

See how to insulate your home.

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An ac does better on auto.

heat rises. put the ac upstairs