brand new a/c not able to cool to 72degrees when 90degrees outsid

9 years ago

We just replaced a freon 3-ton 10-seer A/c and coil with a R410A 3-ton 13-seer a/c and coil. The brand new a/c is unable to cool the house down to 72 degrees when the outside temp is above 90 degrees (most summer days here in the south). Best it can do is 76 degrees and it only cuts off for a few hours at night. Filter is brand new. Outside unit is clean. The company that installed it said it was because we had a few vents closed off. We have had all of them wide open for 4 days now and no change to the problem. One bedroom reaches 80 degrees on these days. We did not change anything at all except the a/c and coil. The vents that were shut off had been shut off for 10 years with no problem. The old a/c could easily reach 72 degrees. What is going on here?

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Comments (8)

dovetonsils
9 years ago
Are they refusing to come out and check out the system? Wow, that is scary. I'm in the market for a new system soon and hope I choose a contractor that is better than that. Is the air coming out of the vents cold, not just "cool"? Any way you can measure the air from the vents?
PRO
CJ Mechanical of North jersey llc.
9 years ago
measure temps at evap coil before and after. see whats going on.
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Nope he didn't check anything other than a couple of quick temperature readings. I'd say he was in and out in about 15 minutes. I set the CFM myself before he came over. They had left it at factory setting (400CFM/ton/3 ton/1200CFM total) at the initial install, and as i was correcting wiring (hooking up 2nd stage heat, humidifier, dehumidify) I checked the dip switches and set it for 800CFM. I couldn't get comfortable on this setting so I set it back to 1200 for a while, but humidity was too high so now its back to 800CFM. I'm finding out that these guys cut a LOT of corners. When they came for the initial quote the guy spent about 10 minutes in the basement and outside looking at the furnace, then took a rough measurement of the foundation and went to his truck for about 5-10 additional minutes. I reviewed the quote and he had checked a box "yes" that asked if the ductwork was sized for 400CFM, and had written in some figures for Manual J heat/cooling loads. I understand that it is impossible for him to have calculated these figures in the time he spent in my home. He did not look in the attic and didn't ask about the windows, etc. Also did not measure ductwork or count number of vents. After the visit a few days ago temps have been slightly better, however yesterday with a peak temp of 100 measured by my IAQ's outdoor sensor the best the system could do was 77 degrees. I'm going to see how everything does over the weekend where temps should be in the high 80s and if it can't hold a reasonable temperature im going to stop being so polite with these guys. Also, I went through Lowes, and the guy from Lowes was present when the quote was written so he had to have known corners were being cut. Overall I'd say this is by far the worst $6k I have ever spent, and I really wish i could just get my old system back.
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User
9 years ago
Did they check the duct work under the house?
BIG culprit.
Is your attic insulated real good?
diy_er3586
Original Author
9 years ago
The company that installed it did come back out, but they seemed to think that opening the vents would fix the problem. They seemed satisfied with the temps coming out of the registers. They said we might need to take one vent out of a room that gets real cool and put an extra vent in another area. I just don't understand why the ductwork and vents were never a problem before this new a/c. The guy suggested that the R410A units are less forgiving about bad layouts or ductwork. Anybody have any idea why it would be any different? We will probably have the insulation checked, but it wasn't a problem before the new a/c. Thank you all very much for responding. I appreciate the help in solving this problem.
dovetonsils
9 years ago
You didn't mention that you have some rooms that are getting real cool and others that are warm. That suggests that maybe the CFM (volume of air) of the new system is not the same as the old and is not getting evenly distributed within the branches of the ductwork.

As for the R410A being not as forgiving, I would think that 3 tons of A/C is three tons of A/C no matter what the refrigerant.
weedmeister
9 years ago
brand/model of old and new system? Was a ManualJ calculation done to confirm 3 tons?

Models that say they are a nominal 3 tons may actually be something different depending on the coil/blower combination.
diy_er3586
Original Author
9 years ago
Here are the model #s:
A/C Before- Goodman CK36-1A, A/C After- Carrier 24ABB336A340. Although, for some reason when I put my serial number in Carrier's warranty website, it said the model number was 24ABB336A003 (don't know if that's a problem).

Coil Model Before- unknown, Coil After - Carrier CNPVP3617ALA.

I don't know if they did a calculation to determine the size or if they just went with 3 tons because that's what we were replacing, and it had worked fine.

Is there an inexpensive tool to measure the air flow out of each register or do just HVAC people have those?

We know we had dampers in at least one duct back when we first moved in. Do those ever get messed up in the process of replacing the coil?
dovetonsils
9 years ago
Seems to me that your contractor should be verifying that the airflow at the coil is what it should be for a three ton system. Maybe one of the HVAC experts can chime in here, but the coil itself is an obstruction in the airflow and with the high efficiency coils with all the folds and the same blower and motor in your furnace, the airflow may not be what it was with the simpler design old R-22 coil.

Edit: One of the things I learned from the advice on this forum is that it is always risky to replace just a portion of a system.

This post was edited by Dovetonsils on Sun, Jul 13, 14 at 18:41

brand new a/c not able to cool to 72degrees when 90degrees outsid

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dovetonsils

CJ Mechanical of North jersey llc.

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brand new a/c not able to cool to 72degrees when 90degrees outsid

Comments (8)

dovetonsils

CJ Mechanical of North jersey llc.

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