central air

[Markbnj]

Ours is a retrofit, and only has one return in the middle of the upstairs hall. It performs much, much better than your system does now, based on your reports. Also, based solely on the statement the contractor made to you that you should leave the system on all the time because "it's cooling," they are idiots. Any further money/time you spend with them will be wasted. Get someone in there who actually knows what he or she is talking about.

 

[Red Squirrel]

Ugh, ductwork in the attic. Don't get why some installers do it that way. Pain in the butt to access. That and the heat of the attic does not help even if they're insulated some still radiates through.

Is it at least solid duct or is it flex? If it's flex it could maybe be bent somewhere. Its hard moving around in an attic, it's possible someone put their knee over it while moving around.

 

[skull]

Ours is a retrofit, and only has one return in the middle of the upstairs hall. It performs much, much better than your system does now, based on your reports. Also, based solely on the statement the contractor made to you that you should leave the system on all the time because "it's cooling," they are idiots. Any further money/time you spend with them will be wasted. Get someone in there who actually knows what he or she is talking about.

The contractors may or may not be idiots. If they did a manual J to correctly size the unit it could be designed for both units to be running and for them to both be on all the time. Manual J is the industry standard for sizing. Ideally an A/C will run 24/7 when its at design temp outside. Thats when its most efficient starting and stopping all day wastes energy. Your unit is grossly over sized(i.e. inefficient) going from 85 to 70 in an hour. This could also be why you have to have it so cold because an over sized A/C doesn't run long enough to remove humidity. You sound like one of those idiots I encounter all the time that set the heat to 80 in the winter and the a/c to 65 in the summer. Mine stays at 77 in the summer feels great and costs me almost nothing every month.

 

[WackyDan]

First...

I'd run the other unit as that should help a lot... especially if the cold air return is shared.

Second... That one unit should be doing a better job... Just because the installation is new, doesn't mean there isn't a problem. We had a name brand unit put in in 2007 and had to have it looked at every year since for low refrigerant... They botched part of the install... and this year a different service company found a leak in the aluminum evap coil.... Something extremely rare.... Spent a lot of labor $$$ to replace that coil and valve even though they were under warranty... and it was leaking from day 1... Hard to prove even with the service receipts from 2007 on... (TRANE - YOu can blow me)...

So... Call a DIFFERENT HVAC service company to check it out. They'll have it in their best interest to gain you as a customer and resolve the issues for good. Don't be surprised if they find your original installer took shortcuts or some other nonsense.

Run that second unit... It should help overall.

And FYI... Closing dampers and vents doesn't necessarily improve performance...I can actually make things worse... and put more load on your blower, reducing it's service life... Which is another reason why in retrofits, they don't recommend you buy those stupid expensive restrictive filters...

 

[rh71]

My first floor was running a while, and then the 2nd floor kicked on (it had reached its temp previously) and only at that point did I hear the return on the 2nd floor start to suck air. Maybe the return doesn't even start if the 2nd floor isn't on when only 1st floor is... testing continues.

 

[Pr0d1gy]

I hate it for you man, nothing sucks worse than lackluster AC. You should call a professional, hopefully one that you trust.

 

[Markbnj]

The contractors may or may not be idiots. If they did a manual J to correctly size the unit it could be designed for both units to be running and for them to both be on all the time. Manual J is the industry standard for sizing. Ideally an A/C will run 24/7 when its at design temp outside. Thats when its most efficient starting and stopping all day wastes energy. Your unit is grossly over sized(i.e. inefficient) going from 85 to 70 in an hour. This could also be why you have to have it so cold because an over sized A/C doesn't run long enough to remove humidity. You sound like one of those idiots I encounter all the time that set the heat to 80 in the winter and the a/c to 65 in the summer. Mine stays at 77 in the summer feels great and costs me almost nothing every month.

I completely trust the contractor that sized and installed our unit, and I don't know anyone whose A/C unit runs constantly to keep the house at the desired temperature. I've never experienced an installation, in 40 years, residential or commercial, where the unit was sized to operate 24x7 in order to maintain temperature. Beyond that, no, we don't set the temperature to 80 in the winter and 65 in the summer. It's 74-76 year-round.

Edit: really, 68-76 year-round. We tend to set it 68-72 in the winter, and 74-76 in the summer.

Edit2: information on the manual J method of calculating heat load that I can find indicates the goal is to have the system sized so that it operates continuously at 110 deg. F. The cooler it is below 110 deg. F. the more the system should cycle. Based on that, and the operation of our own system, I would say it is properly sized. We don't have a humidity problem. It's also even clearer, having read the information on the calculation, that the OP's system is not functioning correctly. Given the advice he has received from the contractors I stand by my original assessment, and that's about all I have to offer on this thread.

"There is no exact answer for how long your system should run during
each cycle. The average air conditioner is sized to remove the heat
from your home as fast as it comes in, on a 110° day. Therefore,
ideally, on a 110° day the system should be able to keep up with
the incoming heat, but not gain on it and be able to turn off. The
cooler it is below 110°, the more the system will cycle on and
off."

http://www.chasroberts.com/knowledge-center/faqs/#6

 

[skull]

I completely trust the contractor that sized and installed our unit, and I don't know anyone whose A/C unit runs constantly to keep the house at the desired temperature. I've never experienced an installation, in 40 years, residential or commercial, where the unit was sized to operate 24x7 in order to maintain temperature. Beyond that, no, we don't set the temperature to 80 in the winter and 65 in the summer. It's 74-76 year-round.

Edit: really, 68-76 year-round. We tend to set it 68-72 in the winter, and 74-76 in the summer.

Sorry I confused you with someone above that said they keep it at 65. I shouldn't of said 24/7 a properly sized system would run 24/7 if it was constantly at design temp outside. In reality a properly designed system will run all day on the hottest day of the year and still maintain the set point.

For the record i'm a certified HVAC tech and an asshole.

 

[Pr0d1gy]

For the record i'm a certified HVAC tech and an asshole.

i.e. Exactly what the OP needs.

 

[Markbnj]

Sorry I confused you with someone above that said they keep it at 65. I shouldn't of said 24/7 a properly sized system would run 24/7 if it was constantly at design temp outside. In reality a properly designed system will run all day on the hottest day of the year and still maintain the set point.

For the record i'm a certified HVAC tech and an asshole.

And, at least in the first capacity, I will defer to your expertise 🙂. So do you think the OP is getting good advice from this contractor? Because to me it seems he isn't.

 

[jagec]

Sorry I confused you with someone above that said they keep it at 65. I shouldn't of said 24/7 a properly sized system would run 24/7 if it was constantly at design temp outside. In reality a properly designed system will run all day on the hottest day of the year and still maintain the set point.

For the record i'm a certified HVAC tech and an asshole.

Isn't 5 tons total capacity for a 2700 sq ft house about right? Obviously it would depend on a LOT of other factors, but that should be in the ballpark, no?

The fact that the OP doesn't hear any air going into the return when the first floor unit is running is odd. OP, are you sure that you only have one return? Can you trace the vents and try to figure out where the first floor handler is connected?

Edit: Oh, and if you haven't changed the filters in a year, do it now!

 

[rh71]

As for changing the filter... I will... but this cooling issue was also a problem last year - the first time they came to try and adjust the vents.

Isn't 5 tons total capacity for a 2700 sq ft house about right? Obviously it would depend on a LOT of other factors, but that should be in the ballpark, no?

The fact that the OP doesn't hear any air going into the return when the first floor unit is running is odd. OP, are you sure that you only have one return? Can you trace the vents and try to figure out where the first floor handler is connected?

Edit: Oh, and if you haven't changed the filters in a year, do it now!

Yeah I'm sure there's no return for the 1st floor. We did a full-house renovation that had them doing layout stuff on the 1st floor and I saw everything done on a daily basis. At the time, I knew nothing about CAC otherwise I would've said something back then. I just double-checked and that one return on the 2nd floor... both 1st & 2nd floor air handlers connect directly into it.

So not sure why it's only sucking air if the 2nd fl system is on (confirmed). And not sure why we have 2 separate units if the return only works like that. I requested 2 separate units to save on wasted energy, but they should've mentioned it would need another return... and asked me to pay for it too. Any ballpark $ on that if it had been done at the same time? I think it was like $13k for this CAC system installed, but that was going through a general contractor, not these guys directly.

 

[Kwatt]

It sounds like you have package units. Is the duct from the air return intake at least double the capicity of the duct after the split back to the units?

Has anyone done superheat calculations? To see if both evap coils are recieving enough warm air.

I would not pay anyone to redo a job that they did wrong in the first place.

I have never worked for or hired a contractor that would not cut any corner they could.



.

 

[rh71]

UPDATE: they came to inspect it and after using some gauges decided to increase the pressure / amount of R410a in the condensor outside for the first floor. He then measured the temp at the interior vents and they were just below 60F afterward, definitely some difference from before. He showed me the small metal tabs at each duct in the attic so I can do the balancing on my own (fstime was right), though it wasn't really clear if opening some would take away from others. I can feel a difference in the house after 30 mins, though it started at 79F rather than 84F like last time. As for the return not coming on if only the 1st floor is on, he explained it's because the duct going to the 1st floor air handler is much longer and if it really wasn't sucking air, the air handler would show condensation around the lines. The 2nd floor air handler is only about 10ft to the return whereas the 1st floor air handler is more than twice that. He also stated that these are designed to drop 1F per hour. He did say that it wasn't the norm with just 1 return on the 2nd fl, but the way the 1st floor layout was designed, there just isn't any place to put the equipment on the 1st floor (it's really open).