Looking for some input and help.

Scenario

Our 23 year old Rheem unit was not keeping GA home at 76 degrees anymore on 85+ degree days.

R-22, 2 ton, 10 seer unit replaced with R-410A unit 2 ton 14 seer. Two units actually replaced just because of the age, upstairs and downstairs units, both the same.

Upstairs Unit still not cooling.

Tech is a friend of a friend.

After install has returned 3 times trying to figure out issue with no success will be back soon but I am looking to find more information.

AC unit in Question is in non conditioned attic with Sofit, Gable and Ridge Vents (Ridge vents added when roof was replaced 2 years ago)

Only AC was replaced, IE Evaporator with TXV, and condenser ect. N type evaporator (maybe that is the norm for 410)

My Background

I am a retired Automotive Master Technician, I was certified for AC with IMACA and ASE AC Certification, so I have an understanding of AC systems in general.

Numbers for problem unit (in 100 degree attic)

88 degree outside temp

Temp at return vent 77

Temp at supply vent 71 (Delta T = 6 degrees at ducts)

Temp at filter in plenum 80 (heat gain on return ducts 3 degrees)

Temp in plenum after evaporator 70 (Delta T = 10 degrees)

3 ton fan set on medium high (4 speed)

Number for OK unit (unit is in unfinished basement stays cool)

Temp at return vent 73

Temp at supply vent 53 (Delta T = 20 degrees)

3 ton fan set on medium high (4 speed)

My thoughts and understanding

I am under the impression of 16-20 delta T is normal. I understand vent temp may not be at that range due to flexible ductwork or leaks gaining heat in attic, but 3 degrees gain on return and 1 degree lost on supply does not seem like it should cause an issue. Otherwise the Delta T at the evap gives me concern.

The downstairs unit has no issue keeping 20 degree delta during the same time. Which means the evaporator is capable of 20 or more degrees of cooling. Same fan, evap, condenser ect.

- Heat soak does not seem to be the issue as the Delta T seems wrong.

- Fan seems to be blowing at same speed as downstairs unit.

- Delta T between the two units should be comparable ???

- High side line at evap is not very hot, low side at evap is not very cold. (I can get exact measurements if needed. (I am familiar with R22 hot high side and cold low side Maybe 410 is different)

- Fan seems to be blowing at same speed as downstairs unit.

- I do not know the pressures, I have a set of Snap-On R-12 Gauges I have used for R-22 only in the past, but I don't have 410 to purge them, and I don't trust the higher pressures on them either. I could put them under vacuum to get rid of non condensables but I don't want to lose any charge.

- I do not thing the lines were brazed with nitrogen in the lines. I am pretty sure he only pushed nitrogen into the system as a leak test after brazing, so maybe debris got in the TXV or something else. Brazing was 45% silver.

Conclusion-

Delta T seems wrong so trying to determine the issue.

- Low charge may be causing the issue (due to low temps for high pressure line and high temps for low pressure line, again just testing based on feeling them, sorry I know that is vague, but they did not even cause any discomfort on either line holding them, normally high pressure lines get uncomfortable when you hold them for too long, same for low pressure lines.)

- TXV issue, but I doubt that because I would expect high temps on high pressure line and with high temps on lower pressure line which I do not see.

- Low heat soak/loss on return/supply, combined with evap delta makes me rule out the attic temps.

Sorry, I know that is a lot just trying to give the info I have as it technically does not make sense if everything is right, but I do not think everything is right, even though the tech seems to think that an AC unit in the attic with the outside temperatures makes it acceptable.

Thanks for your time reading this and an early thanks to any feedback.