Why won't my central heat and air cool my house?

Your answer is in your question. I'm really surprised no one caught it.

You said "thats if we turn it on after we get home around 5". There's nothing wrong with your air conditioner. Its having operator problems. And the thing may be slightly undersized.

I get this several times a day. You cannot expect your air conditioner to just start cooling your house when everything inside the house has had time to absorb heat & humidity; the walls, the furniture, the cabinets,..... everything. When those triple digits come, your system needs all the help it can get.

You gotta set the thermostat at around 75 degrees and leave it alone. You can mitigate some things like put an exhaust fan in the attic. Get some awnings on the windows to keep direct sunlight out. Keep your filter changed. I hope the pros made sure the refrigerant charge was right and leak-free.

-Both condenser & evaporator should be extremely clean and free flowing. Things like this are capacity robbing problems that are easy to control.

If you are still having problems,... buy a couple of small window units and put them in the west windows, and run them on medium during those high stress afternoons.

A home air conditioner is designed to give you a 25 degree drop from outside air to inside air. You are probably getting this. If it is triple digits outside, and you are getting down to 80 indoors, this would be about right. You can try adding fans.

If sunlight is hitting your outside unit, try to create some shade for it. Check to see if there is anything obstructing your "A" coil such as animal fur, if you have pets, and stuff got past the filter. See if your blower motor is set to the highest setting for air flow.

If you are turning the unit on in the late afternoon, this means the system is trying to play "catch-up". You might want to leave it on while you are gone, set to, say, 82, so that it does not have as much to overcome when you get home, or buy a thermostat with a timer on it and have it come on before you get home.

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Well said above.

When your indoor temperature is within 5 degrees F of the thermostat, check return air temp and supply air temp. If the difference between those two temp is 15 - 20, the system is very sound. But if it's below 15 degrees F, low freon or inefficient air flow (inside or out) could be the cause.

It's been proven that a/c running at decent temp for all day doesn't consume much more energy than periodic hot pull down.

Please try this method, and if still suspicious of you unit, call at least few technicians for proper diagnose.

good luck.

first clean your outside unit turn the power off and spray it with a hose from the inside to out next clean your a coil there the ones on the inside of the house if you can access them next clean the blower wheel a vaccuum will work in both these places next keep your air filter clean change it once a month next keep the unit on all day dont turn it off when you go to work keep all of your blinds and curtains shut if all thyis fails have a good well trained hvac company look at it

Check your atic vents make sure that they are not blocked. You may need more venting and insulation in the atic. http://www.doityourself.com/stry/h2addatticvent