Air Conditioning - New AC airflow doesn't seem cold

I had a new Carrier 3Ton 10S.E.E.R unit installed in July of last year to replace a similar Bryant model that the service person indicated had a bad condenser. Since the new unit was installed, the air coming out of the air ducts does not seem very cold - or at least not as cold as I was used to with the prior unit which was also a 10S.E.E.R. I had called and asked the installing company about it and they sent someone out who said the coolant was a little under what it should be and so they put more in. This helped a little but it still doesn't seem to cool the upper rooms of the house and it is only a step ranch so it's not like 2 full floors or anything. Then, to make things a bit more confusing, the new unit was serviced for a regular tune up in April this year - cleaned and tuned - and the service person (from the same company) said the coolant was too high as it was and reduced it. The air seems worse again as it only comes out in vents on the first floor at 60 degrees when the air is on. (I have a regular temperature gauge in the vent in the kitchen to help me get an idea of what is going on.) I am wondering what the regular range of air coming out of the vent should be. The 60 seems steady - or rather, not dependent on the house temp when the unit comes on - it could be 77 or 81 in the hourse and 60 is what the air temp will register in the vent - so I am guessing the cooling is not based on lowering "from" a range, but is a constant. Is 60 normal or should the air coming out of a vent be lower. This vent is on the first, rather then, "upper" floor. The upper rooms do not get air that is that cool. I don't know what to ask about or how to help my coooling guys help me find out why this unit feels so less cool then the one it replaced. I am hoping for some feedback on what a normal reading is from a vent from a central air unit, so I can try to address it with the service providers if the air is indeed warmer then it should be expected. Thank you for any help you can provide me. I appreciate it.

In general, about 18-22º difference between incoming & outgoing air is considered to be a good temperature drop. These temps should be measured within a few (no more than 5) feet of the indoor unit.

What I get, before my eyes cross, reading your post is that you have a 60 degree supply temp with 77 to 81 return temp.

Meaning 77 to 81 entering the evaperator (cooling coil) and 60 out. That is a 17 to 21 degree "gain" in cooling.

Notice how I use the ENTER key to seperate things?

You are on the very high end of what a home inspector would except as far as cross coil temp. Air temp at the return verses air temp out. What is the air temp upstairs? From the supplies?

A Bryant and a Carrier (depending on vitage) are basically the same except Bryant is cheaper.

From the huge block of text (I'm picking on you now, don't be offended). I think you have two problems. One, your air flow is incorrect, to low. And since you have had refrigerant added and taken out, your charge is incorrect.

Basically your install was not done correctly. And, your service since then has been sub par.

Chris

For a 10SEER unit a 16-18F Difference is the norm for difference of supply air from return air in the cooling mode. Any cooler and you would have a lack of air flow problem causing the freon to slug back to the compressor. (freon not changing back to a gas efficiently)

Use the SAME thermometer check the air right before the filter for the return temp and the air leaving the unit in the plenum

If you are using your thermostat for return air temp and a temperature prob for supply air temp this would be the incorrect way of measuring a temp difference.

Next what type of Heat do you have?
Gas Furnace
Electric
Heat Pump

What you really need is the Carrier Dealer to come out and explain everything and show you what they are doing not just say it's ok.
If you feel you have a problem with rooms not cooling,
but the Temp Difference is ok
Then like mentioned before you may have a air flow problem or a Heat Gain problem in your particular rooms.
I would recommend you talk to the service manager or the person who holds the license and ask them to come to your home to explain what is going on.

I'm kind of questioning though the Carrier Dealer,
Why did they replace your unit last summer with a 10 SEER model?
in 2006 minimum SEER rating was 13
Did you get both indoor and out door units replaced?