why my ac runs all the time but does not cool.pressures are all ok,coils cleaned,just runs constantly when hot
Answers:
It sounds like you did a good job of trouble-shooting the equipment. When you say the pressures are o.k., that indicates to me that your refrigerant is at the proper level.
Given that the gas is o.k., there are two big reasons for your problem to occur. One, a duct that has worked its way loose, or two, undersized equipment. The reason I think it may be undersized is that your question seems to indicate that it works o.k. when it is cooler out.
You should have at least 12,000 b.t.u's (1 ton) of cooling capacity for every 500 feet. A 1500 square foot home under air typically would have a 3-ton unit. This can vary widely with extremes of glass area and r values of insulation. Bear in mind that tonnage also refers to the cubic feet per minute produced by the air handler. A unit that is undersized will not only short you on cooling b.t.u.'s, but air flow as well. If your air is trickling meekly from your vents, I think we can assume undersized equipment.
If you are not prepared to upgrade the equipment and ductwork, you can consider (at least in the short run) augmenting the cooling b.t.u.'s with window units. (cheaper, but not terribly efficiant.)
One last thought. Sometimes the heat strips will kick on during the cooling cycle. Make sure this is not the case.
Other answers:
check freon?
check freon?
Check your freon. But make sure you hire a technician to refill it.
It may be that it is froze up on you. Try to turn it off and let it sit for a while to thaw. If that is it then do not set it to such a low temp. It will ask to much, make it work to hard and then freeze up again. There is no way you can check your own freon. It takes a machine that removes it weighs it to see how many pounds were in it and if you were low. You need to take it in or have someone come to you to repair it if it is not froze.
Low BTU capacity for the room to be cooled or bad thermostat.
How did you determine your refrigerant level is "ok"? If it truly is, your a/c WILL run constantly when the temp is 95f , because that is the high end of the design temp. But, if its not maintaining temp in the house, check your duct for proper insulation (ESPECIALLY if return runs in the attic), and make sure your supply and return grilles are not restricted / blocked. A simple test that you can do to test your systems efficiency is to check the supply air temp vs. the return air temp. You want a 15-20f difference between the two. If there isn't a sufficient temperature difference, your unit may not be performing properly, or back to the duct investigation.