Air Conditioning - How to tell AC is working ok

My AC unit is 2 ton large and it is more than 30 years old. It is centeral air conditioning. It think it is 6 SEER as any AC befroe SEER ratings consider as SEER of 6.

It runs only 5 minutes and shut down. Cooling is ok, I don't feel hot as temp. is fine for me.

Is any thing wrong here. Why unit is running only 5 minutes? Does it need Freon. I think there is a change from last year.

My apartment unit is 13500 cubic feet and every room has large window. I assume at the time of AC installation they must have checked it about the capacity of AC unit needed. I live in south.

By having this limited information, does 2 tons AC for a 1500 sq ft. apt. (9' ceiling) too big?

If the thermostat is also old lets replace it with a nice new one that could be your problem since 2 ton for 1500 sg ft should be a hair small (using the 500 sg ft per ton rule of thumb) and the unit should run too long instead of short cycling. Also take a close look at the location of your thermostat if it is getting air directed towards it from a vent close by it could also cause short cycling as the thermostat thinks things have cooled down but it is simply being affected by the cool air from the vent.

Blower clean? Filter clean and new every 30 days. Check the copper lines at the outdoor unit. Small line can be just a little warm or at air temp and big copper line should be cold and wet when on. If so unit is OK.

ED;)

I change air filter every 3 months. I use these white material filters and it does say on them change every 3 months.

What is a blower?

I will check copper lines and themostat this evening.

I have checked my AC and thermostat

Thermostat controller is not any where close to air vent and there is no direct air coming to the directions of themrostat.

Air filters clean.

I have checked the copper lines.

Small one seems to be at outside temp. and big one was not cold but there was temp. difference beteen small and big one. In addtion big was not wet while AC is working.

Some thing wrong here.

I was reading here about regular maintainence of AC, some one mentioned that he is also cleaning/rinsing coils of outside unit.

I have never done any thing to outside unit. Where are these coils located?

I am new to HVAC systems. Sorry for lots of question.

You may have a low pressure sensor on the low side cutting the unit off as the low pressure drops below about 50.

You need to determine if the thermostat is shutting it down or is the inside unit continuing to run while the condensor outside shuts down.

[QUOTE]Small one seems to be at outside temp. and big one was not cold but there was temp. difference beteen small and big one. In addtion big was not wet while AC is working/QUOTE]
If everthing else is ok. You have to call a HVAC guy or gal freon Charge is low

ED;)