Our AC (Heat pump)is blowing hot air in the afternoons as the temperature outside rises. We have had the freon checked and it is okay. The AC will blow hot air for about 30 minutes then blow cool air. Our thermostat is set at 76 but it is 82 in the house. What is wrong with it?

No heat pump will put out much, if any at 6 degrees.
A heat pump is an air conditioner that reverses cycle via a reversing valve that re directs the refrigerant flow in the unit, in ac mode,
heat from indoors is rejected outdoors in the heat mode the heat from outdoors is rejected indoors.
The system does this by evaporating and condensing refrigerant.
For the refrigerant to be "boiled" or "change state" from a liquid to a vapor a temperature differential must exist, meaning the heat from the outdoor air must "boil" the liquid refrigerant.
For this to be possible the liquid refrigerant must be colder than the 6 degrees ambient or it will not boil anything.
For a refrigerant used for AC to be that cold the pressure will be in a vacuum for most refrigerants temperature pressure relationship.
Heat pumps below 40 degrees ambient outdoor temperature are
not effective, at this temperature outside drops a degree lower it further degrades the heat output .Power companies that finance Heat pumps typically will install an outdoor thermostat to prohibit the 2nd stage or electric heat strips from coming on until it is 40 or below outdoors, at a certain point well before 6 degrees a heat pump should be ran on the emergency heat mode which is the heat strips and the fan. Since 1500 Watt electric heaters are available at Wal-Mart for $20 the best alternative in this situation would be to buy a few of them.

Heat pumps are the same as an A/C unit only it works in reverse. Instead of blowing cold air inside and hot air outside it blows hot air inside and cold air outside. The heat being blown inside is extracted form the cold air outside. Its called Latent heat Latin for hidden. Believe it or not even though its 20 degrees outside there is still heat in the air. Example if you want to drop the temperature of a freezer from 20 to 10 degrees you have to remove heat .I know your getting unusal weather and that is the problem. Heat pumps can only work no lower then around 20 degrees outside.Heat pumps are never used above the freeze line. With your unusal temperatures thats basically where you are now. Ride it out. When your temps rise a little your be fine. Im in Chicago.

sounds like you have a leak concern if they are adding freon

however, it also sounds like a restriction in the system and/or a defective TXV

do you have pressure gauges... this is the only way to diagnose an a/c system without just throwing parts at the concern

Find a reputable HVAC contractor to do a room by room analysis with heat and cooling loads calculated and units sized and duct requirements and compare to what you have.

The air not being cold is not necessarily an indicator of anything malfunctioning. High efficiency units for instance don't produce cold air.

Since you have had someone look at it, the duct work may be collapsed which restricts air flow or uninsulated which warms up the supply air. Either one is a possibility. Any Cox Cable guys been stompin' around your attic lately? Wouldn't be the first time.

Usually, when the air coming out of the vents is not cold enuf it's because your freon level is low. Probably leaking, but they can usually recharge the freon and it will work for a while. Try another repair company and see if they can recheck the freon level.

We have a high efficiency unit and it produces cold air, so I don't know what previous poster is referring to. Air conditioners are supposed to blow cold air.

Sorry, to tell ya but it is normal if the outdoor temperatures are much below 45 degrees. Below 45 degrees there is little heat outdoors for the heat pump to grab to heat the home so it will run 24/7 and blow cool or cold air. Below 45 the temp of the air coming out the vent will decline and you will get no heat from the heat pump itself as you near freezing.

Your emergency heat or auxiliary heat is electric strip heat. But it only kicks in during normal operation if the temp in the house drops 3 degrees below the setting. (some tstats if can be 5 deg.) Otherwise the heat pump will blow cool or cold air the rest of the time if it is too cold out.

To prevent it from running all the time and blowing cold it is recommended if the temp outside is falling below 45 degrees you should just switch to the emergency heat setting, which shuts the pump outdoors off, and just heat with the electric.

But if there is no heat outside the heat pumps will blow cold. They are the cheapest and most efficient forms of heat but only as long as the outdoor temp is above that 45 deg..

I'm guessing that if you haven't experienced this you live in some place with moderate winter temperatures like in Northern Florida and rarely get very cold winter temps like the freezing you have seen there recently.

It will likely blow much warmer when the outdoor temp rises.

freon is low or outside is very cold

If it does not have a furnace or heating elements for heating, then it is a heat pump, which is rare for a central AC system, but makes sense of the fact that it blows warm air when you reset the pressure switch, which may indicates freon pressure charge problem if your AC system has a reverse valve and uses freon to for heating (heat Pump).

Do you get heating when outside unit runs? if you do, check freon pressure levels and top up to required pressures. The button you depress is a pressure reset switch ... that is if your AC system is a heat pump ... which, as pointed above, it is not common for central ACs.

Sounds like compressor not running. may be a bad capacitor, could also be low on freon.

It sounds like it is your high pressure switch located on the high side supply line of your AC. When the temperature is hot, it is harder for the condenser to cool off the freon flowing through it causing the pressure in the system to rise. Also, check to make sure that you condenser on the front of the truck is clean and free of debris. If you have an electric fan, make sure it is coming on when the AC is turned on.

Hope this helps,

Jeff

Before doing anything I would have the freon level in your AC system checked, freon leaks are quite common and easily repairable by a specialist.

MAKE SURE THE CONDENSER IS CLEAN AND THE FAN IS WORKING. DOES EVAPORATOR FREEZE UP? IF DOES LOW FREON LEVEL OR BAD EXPANSION VALVE