Air conditioner runs constantly, doesn't cool much

We have a four-year-old central air conditioning system that ran fine until this summer, but now isn't doing so well. I don't believe the air is coming out as cool as it used to, and the system runs almost constantly but does not cool the house as much as it used to.
(We have a "Space Pack" system, by the way.)
The company that installed it came out twice in one week to check it, and checked the attic components as well as the outside unit. They have found nothing wrong. However each time they said it needed "half a pound" of freon. Does that sound right?
The service order from the second guy who came out said he used 1.5 (lbs?) of CB222, and that he "moved the Exp. bulb."
We have replaced the filters. Today as a test I turned the thermostat way down (from mid-70s to mid-60s). The system ran constantly but the house only got a slight bit cooler.
Any idea what the service guys might want to check next?
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snipped-for-privacy@advancedbionutrition.com wrote:

How hot was it outside? If your house was in the mid 70's and it is in the 90's outside, thats probably as cold as you are gonna get. It's not a refrigerator. It's an Air conditioner. If it is 90 outside, dont expect your house to get into the 60's... Thats not how these systems work. And if you set you stat to something like 65, then yes, the system is going to run all the time, because you are trying to make it reach a set point it is not designed to reach.
On the other hand, if the service tech has to add refrigerant to the system, there is most likely a leak somewhere in the system, causing you to loose the initial charge.
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They will probably want to check your wallet and your IQ to see if their little pot of gold is still intact.
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Setting your thermostat down to 60 is really ignorant.... The *normal* indoor design temp is 75 @ 75% relitive humidity. If you really want to give up all that hard earned cash to the power company, then turn the stat down to wherever you want it. Just keep in mind that when you get the house below 68 degrees, the evap coil is gonna freeze. I can't change the laws of physics. As far as adding refrigerant (FREON is a registered trademark of Dupont), just a fraction of an ounce can make the differance between over/under charged, or being correctly ballanced. I would highly recommend that you find a *competent* tech tho.... it will save you a lot of money down the road.
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