I have a fairly new Carrier AC, serviced regularly. Each time it is checked, the service man says all is working well. Then the hot spell comes, and I can get no cool air during the hottest part of the day, and it comes on and works just fine in the late afternoon through evening.
I did have a programmable thermostat, which I have now replaced with the basic model. It seems to be the same hours every day that the cool air disappears, but the blower keeps going.
Very frustrating, any ideas?

Unit sized to small for your house.

Refrigerant overcharge causing high head during the hot part of the day

Non condensibles in the system causing the unit not to produce the rated BTU's

A question for you. Does the outside unit just shut off when it gets hot or does the fan outside still turn?

You would probably know this but do you have a deal with the utility company that allows them to control your outside unit? Some utilities offer this as a way for you to save money on your bill and lower the demand at the electric generation plant. Usually the utility company will have you sign a paper then they will install a circuit interrupter device that they control.

Unit sized to small for your house.

Refrigerant overcharge causing high head during the hot part of the day

Non condensibles in the system causing the unit not to produce the rated BTU's

A question for you. Does the outside unit just shut off when it gets hot or does the fan outside still turn?

You would probably know this but do you have a deal with the utility company that allows them to control your outside unit? Some utilities offer this as a way for you to save money on your bill and lower the demand at the electric generation plant. Usually the utility company will have you sign a paper then they will install a circuit interrupter device that they control.

[B]The outside fan keeps running when it gets hot, just no cool air. I do not have the agreement with the local utility company, though I am aware of this practice. I sure hope its is not too small for the house, since I just purchased it. It is a split system - what does that mean?

Split means that the condenser is on the outside of thre house and the evaporator is on the inside of the house. If the outside fan is running then the compressor must not be running. It could be going out on overload or many other things.

How many square foot is your house? What area of the country are you in? This may help to get a ballpark on the corect size of your unit and what is the size BTU capability of your A/C unit.

Might be a good time for you to call for professional service.

Try taking a water hose to the outside unit and washing it, it may be dirty and going off on the compressor internal overload. Be careful not to get the motor wet .

Split means that the condenser is on the outside of thre house and the evaporator is on the inside of the house. If the outside fan is running then the compressor must not be running. It could be going out on overload or many other things.

How many square foot is your house? What area of the country are you in? This may help to get a ballpark on the corect size of your unit and what is the size BTU capability of your A/C unit.

Might be a good time for you to call for professional service.

I appreciate your help. My house is about 1300 sq.ft. It is the compressor that is failing to cycle on when the weather heats up. BUt, I am thinking more along the lines of a program that is incorrectly set. The unit stops about the same time every day which is why I changed the programmable thermostat. Today it hasn't gone off yet, and I have the temp set way down, its hot outside and things are working normally. It is a puzzle, but I will take your advice and call a professional. It is really hot here in San Diego this week-end, and by the time I get a pro here, it will be cool. Oh well, life in the big city!