Blower CFM sounds good. ESP sounds within range. Split temp I'd like to see more closer to 20*, but 17* isn't terrible. The FIVE supply registers REALLY jumps out at me. You're pushing A LOT of air through those registers. I think you need some more registers, and another return wouldn't hurt. Was this system sized properly? If it's oversized, it will run up the electric bill with it's constant cycling on and off. Good luck. Please provide square footage of addition.

The addition is 800 square foot with 14 foot ceiling. I can tell you the technician said it was properly sized but you know how that goes. The system does not short cycle, it actually runs for quite some time to make a slight temp change. What size and number of registers would be good?
I had a Honeywell thermostat that controlled at .5 degf so I removed it and installed one with differential adjustments and it is set on 2 degf.

river

what are normal run times? how many minutes off?

at what outside temp?

Have the tech lower the fan speed to 2 tons since you have a 2-ton unit (so 800 CFM). That should give you a better split temp (if the unit is charged right to begin with). 5 registers might make sense then, but that still seems like a lot of airflow for 2 tons. Is there a lot of velocity out of the vents?

The run times are about 20 to 30 minutes for a 2 deg change on a 90 deg evening. Off times vary about 10 to 20 minutes. With five registers and the air handler set to 2 tons and 880 cfm with 20 deg split , is this the proper setting given the room size? I realize with a higher setting I will need more registers. Yes with the current 2.5 ton setting the velocity is high. So should I leave the air handler at 2.5 tons and add some ductwork or lower the air handler and leave the ductwork alone? If I need to add some registers What size duct would you recommend?

river

while you don't say area you live and the importance of good dehumidification, I agree with Ryan about dropping air handler setting to 800 CFMs and try this for awhile. It should help with any noise concern and ductwork modification may not be required. then take another measure of temp split.

IMO

I made a mistake when I said I have (4) 8" and (1) 4" supply registers. While lowering the blower speed we noticed there are (2) 8" (2) 6" and (1) 4". With the current blower speed at 890cfm, will this be ok?

If the tech measured the static and it was okay, and the velocity coming out of the vents is reasonable and cooling the space effectively, then you should be okay. My comment was based on the airflow velocity more than anything. 890 CFM is still high--can you set it to 800 CFM? That's 400 cfm/ton and more ideal for a 2-ton unit to dehumidify and get a greater split temp.

what is an unreasonable velocity because the tech doesn't have a way to measure it.

Does the air seem to come out of the vents at an abnormally high speed? Is it loud? If it's not loud and feels about right, then I wouldn't worry about it. I'd want around 100 cfm per register, give or take. 5 registers at 800 cfm shouldn't be too bad... I would definitely bring the speed down to 800 cfm, though. I think that's the best setting for a 2 ton unit for a balance of sensible and latent (humidity removal) cooling. Static will tell you if everything is "good." Have the tech test the static at 800 cfm and see if it goes down.

OK blower speed is lowered. You can hear the air flow a little but not to bad. Static is .3". According to the blower paperwork, the setting we are now on is a little over 800cfm @.3". Split temp is 20 and copper line is sweating nicely. The figures we calculated are that at this speed the air in the room will turn over 6 times an hour.

You take the ESP just before the blower & just before the evaporator coil.

The static reading you got will be different from the real ESP reading. - udarrell

Here is a link that might be useful: Checking Static Pressures

The air conditioning SHOULD NOT cycle 6 times an hour, if I understand you correctly. This is inefficient and suggests an oversized system. Is that what you mean? If you can, set your thermostat to 3 CPH maximum.

If you are checking pressures on the condenser and you wanted to check the suction, should it pull into a vacum or around 5 to 10 psi ?

After looking at my system here is what I have, a 2 ton condenser with a 1.5ton compressor, air handler with speed options from 1.5 to 3 tons, and a coil rated 1.5 to 2 tons. Since the compressor is 1.5 ton, shouldnt the handler be set to 1.5 tons also? I know you need 400 cfm per ton but this is weird.

I'm confused about the size of the outdoor unit. What's the model number? That will give the capacity. If it's a 1.5-ton unit (which would make much more sense with your register count), then you'd ideally want 600 cfm of airflow (400 cfm/ton). Model number would be something like GSH13018 or GSH13024. It can be found on the nameplate on the unit--above the service valves.

Condenser model GSC130241A

That's a 2-ton condenser. Airflow should stay at 800 cfm (2 tons x 400 cfm/ton).