Btu or sq feet of home

that is a 10000 btu unit and a good rule of thumb to go by when 'sizing' a unit is 12000 btu for every 600 sq ft of cooling space (if the place is well insulated) or 400 sq ft (if not well insulated).
So, you have a 10000 btu unit which is 5/6th of 12000 btu - so - can reasonably expect that unit to cool approximately 500 sq feet.
In other words the room it's in now could be only - say - 300 sq feet (and well insulated) - in which case the AC unit is cooling it - well.
However, if you try to cool a 800 sq ft room - it will not work as well.
Hope this has helped.

Assuming the unit is 'cooling' but not cooling it 'well,' I would think the unit is too small.
NOTE: 2000 Btu for every 100 sq ft of cooling space if the room is well insulated. If not - then 2000 btu for every 66 sq ft.
For example - a 12000 btu AC unit should cool 600 sq feet of cooling space if well insulated.
or
400 sq feet if not well insulated.
hope this has helped.

The AC your landlord installed is rated at 8000 btu which is way too small for 900 sq ft. You need at least a 15000 Btu Air conditioner and a 'well insulated' house to be cool.
A good rule of thumb in the AC business says you need 1 ton (12000 btu) of Air conditioning for every 600 sq feet (if the house is well insulated) - if not - then you will need 1 ton (12000 btu) for every 400 sq feet.
So, if you have 900 sq feet and the house is well insulated you should have at least a 15000 btu unit.
If it's not well insulated you will need 24,000 btu.

Assuming that there are ducts ran upstairs and downstairs, it all depends on the square footage of the living spaces, i.e. bedrooms, living room, dining room, etc. You need an average of 1 cfm per sq ft. For every 1 ton of air, you have an average of 400cfms. So your 5 ton unit will cool/heat 2000 sq ft. A 16 seer unit with a 95% furnace is a nice buy and you will notice the difference for sure. Hope this helps!

You need to have someone evaluate the ductwork for the home. With all zones calling, there should be an even balance of airflow. And when only one zone is calling, there should not be the tornado effect you describe.

The dampers feeding each zone may be of the wrong size. It also sounds as though you are also having a problem with your bypass damper. This damper is designed to bypass excess air when only one zone is calling. It is operated typically off the airflow alone.

Have it check out. You definitely have a problem. I would recommend getting it looked at by a company other than the installing company to remove any bias judgment or diagnosis.

It is 30,000 btu, 2 and 1/2 ton system. Capable of cooling 1200 square feet satisfactorily.

Your unit is sufficient to cool up to 1000 sq ft satisfactorily. You have a 2 ton unit. 500 feet per ton is standard.

A good heating guy should be able to balance your dampers to increase the airflow upstairs. Keep in mind heat rises. 2nd floors are the hardest to cool. You may need to add more returns to pull the heat down the the evaporator so it can be cooled. If you are lucky you may be able to adjust your blower up to a higher speed. You may have to even add some more supply airs. Check with your local building inspector. He may be able to give you a list of contractors in your area that would be good for this type of problem. Good luck>>>

Some of this depends on where the air handler/furnace is located. Most often in two story houses, it's in the attic upstairs, or in a closet upstairs. A duct routes air from the furnace to the downstairs supply duct, so it is a distance from the air handler.
When the unit first initiates a heating cycle, that duct is going to be full of cool air, and the duct itself will be cool. So the furnace has to run long enough to push the cool air out, as well as warm the duct up, before your going to feel warm air at the registers downstairs.

Keep in mind, heat rises. And, your thermostat only monitors the immediate area where it's located. In your case, upstairs.
Two story houses are problematic because of this. And one way around it is to have a damper system installed that distributes the air upstairs or downstairs based on a thermostat located in those spaces. There would be 2 dampers, and 2 thermostats (one upstairs, one downstairs). Each stat would control a damper, and the call for heat or cooling.

Let me know if you would like to consider a system like this, and I can point you to components to use. I've put several system like this in.

Nope its a big room for 24000btu. the computation is 18sqm./ 1 ton. or 1.5 hp.