New Lennox system

[Fireferg73]

Hello, I have a question regarding a new Lennox split system
system info:
Condensor:XC21-048-230-08
Furnace:SL280UH090V60C-03
Coil:CH33-50/60C-2P-3

Do these components match?
I believe the condensor is 4ton and the coil is 5ton

I think the system is oversized due to short run times even when OAT is near 100^. Manual J suggested 3.79ton
This is a 1650sf type five construction single story residence built in 1996 in Tucson, AZ
Insulation in the attic is not great, double pane windows are in ok shape.

All ductowrk is flex, 20 inch return trunk, 20x30 return grill

thank you for your feedback

[hcong]

If manual J was done right and suggested a 3.79 ton then your 4 ton system is fine. I usually don't oversize coils, but I know some do to get higher efficiency. So the coil should be fine.

Is the unit running for at least 15 minutes? How is the temperature in the house? Does it feel comfortable or humid?

[jtrammel]

I would have went with 3.5 tons, man j input numbers are a lot of times educated guesses and most err on the overkill side.

[t527ed]

good match, 49,000 btu's and around 17.50 seer.

with load calc you gave it is sized properly, make sure it is wired and set up properly so it is going into low stage. also make sure blower settings were adjusted for the 4 ton unit and not left on the 5 ton factory settings.

[jtrammel]

Didn't realize it was 2 stage, make sure it is wired for 2 stage, lots of guys don't because they don't want to pull a new wire

[Fireferg73]

I can see in the diagnostics on the Icomfort that it does operate a lot of the time at 70% on the condensor, which is low stage.
Temp in the house feels ok, Rh @ around 35-38% per the stat.

What should the CFM settings be for a 4ton. Manual J stated house CFM needed was around 1400 as I read it.

[jtrammel]

1400-1600 cfm for 4 tons

[Fireferg73]

Ok, first stage is set for 1000 CFM and second stage is set for 1500 CFM.
It seems to do most of its work in first stage, day and night but it definitely doesn't run for fifteen or twenty minutes unless it's really hot outside, like over 100 degrees.
Also, when the condensor kicks on it makes my lights dim slightly. Just ever so slightly. HVAC company didn't think it was a big deal. Old unit never did it but it was smaller and much older technology. I understand all mechanical devices are different.

[t527ed]

have you verified the information used to figure the manual j?

numbers may have been fudged to fit the unit....

[beenthere]

Old unit was a smaller tonnage? Or just physically smaller?

[jtrammel]

Ok, first stage is set for 1000 CFM and second stage is set for 1500 CFM.
It seems to do most of its work in first stage, day and night but it definitely doesn't run for fifteen or twenty minutes unless it's really hot outside, like over 100 degrees.
Also, when the condensor kicks on it makes my lights dim slightly. Just ever so slightly. HVAC company didn't think it was a big deal. Old unit never did it but it was smaller and much older technology. I understand all mechanical devices are different.

Sounds like it is grossly oversized and even the first stage capacity is way oversized, good thing you live a dry climate or humidity would be a big issue for you in the summer.

[Fireferg73]

Old unit was 3.5tons, single stage Rheem 10 Seer coupled with a single speed furnace.
And yes, I agree I need to confirm the J calculations.

[beenthere]

First stage has a capacity between 2.8 and 3.2 tons. So in first stage, its almost as much capacity as your old unit. Its probably the VS blower that can move the air better then your old blower could, that helps it to cool your house better in first stage then your single stage 3.5 ton could.