central air

[rh71]

We had a new system (with 2 units outside serving each floor) put in last year along with the dormer and some vents are blowing out more than others. We had them come back at one point to try and adjust that and they did something in the attic where the ducts are and just said "see how it works out now". Well it's been pretty much the same thing - we really don't complain except when we actually need it like days like today when it's 95F outside.

The system for the 1st floor has been on for 2 hours now and it's still hot at 83F inside according to the thermostat and we have it set to the mid-70s - not likely it will reach that - it was like 85F when we turned it on so it's barely done anything. The system upstairs is off but we closed all the 2nd floor doors. There's about 1500sqft of lateral space for the 1st floor plus the stairway up to the hallway of the 2nd floor (where the return with that large filter is).

Is it normal for a central A/C system not be able to make the area (1st floor) so cold that we'd have to turn it down? 83F is barely bearable.
Is it possible to recirculate to specific vents in the house if some are barely getting any air through?
Is there just 1 setting for the amount the entire system blows out? Recirculating that would make other areas warmer.
Is it a freon issue - we've hardly used it since new but maybe it was never rightly charged.

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).

 

[fstime]

Well one of your problems is a super easy fix.

All ducts should have damper controls from the source (a little handle should be visible) which allows you to restrict or allow more air to that specific duct.

It is good to adjust these if need be, think of giving your central air system a "tune up."

Some systems will be what is considered "2-stage."

If it is lets say, 77F outside and you set your thermostat to 75F, the system will always start in a lower, more power conserving stage 1 mode. In this situation, the system in the "power saving" mode will be able to cool the house fine because it is not that hot outside and you are only asking for a 2 degree drop.

Now if it is 98F outside and you want 70F inside, it will once again start in stage 1 mode but after a few minutes of running, the system will realize it is not cooling the house enough and will then go to the 2nd stage.

I believe for this higher efficiency, you need a variable blower and maybe a specific high efficiency type condenser.

As far as your other issues, I am not sure, especially without seeing it myself. Does the air feel cold? Try putting a temperature gun to the duct to see how cold the air is blowing out.

If it is 95F outside and you want it bellow 70 right in the middle of the day when its already hot inside, I wouldn't be shocked if it was still running after only 2 hours.

 

[rh71]

thx for the explanation - it doesn't seem like it's a 2-stage system. It is now down to 80F after almost 4 hours, but the thermostat is still set to 75F. Also the sun has gone down (temp outside is down to 83F) so it may naturally be easier to cool inside. But dropping the inside air 4 or 5 degrees in 4 hours with a CAC system seems wrong.

The air blowing from the vents is cold enough, but not so cold that I would have to take my hand away in any amount of time. The kitchen vent is blowing noticeably harder, but the same temp, and if we can get that airflow in all vents, we'd probably be better off. With the damper settings, can we get that without affecting the vent in the kitchen? Sounds like yes. Not sure why they would restrict vents in the first place.

 

[Markbnj]

I doubt it's a matter of tuning the airflow in the ducting. Something else is wrong. Maybe you're under capacity for the space you're trying to cool, something is wrong with the air handlers, etc. Sounds like you've got four compressors for two floors, so big house. Where are the air handlers located? Attic? If so is all the ducting up there insulated? Bottom line, if that system were properly designed, regardless of variations in airflow from room to room it would still cool that place down. As it is you're probably running full-time and getting nowhere. Have a pro come in and look it over, and probably a different one from the morans who put it in.

 

[rsutoratosu]

check the ducts also, make sure they're not leaking, ie seal the joints to prevent air lost, you can probably get a cheap cfm meter and measure air flow

 

[rh71]

The air handlers with Ruud marked on them are all in the attic. Supposed to be a good name. Insulation... Its just the silver foil lined ducts running around but organized. Not traditionally insulated by that pink stuff if that's what you mean. How does capacity work so I can try to find out if it's enough to handle it? Total house sqft is 2700.

How cold should it be at the vent? Too cold to keep a hand there for longer than a minute?

We're using the 2nd floor only right now at bedtime and its doing it's job but it's not open like the 1st floor is. But anyway the vent down in my office does nearly nothing when I close the door. Can't feel the air blowing when standing under it, only up at the vent. Trying to determine if it's the temp or airflow or both.

Separate question is if the doors are closed and rooms inside cooling, how does the thermostat out in the hallway accurately reach the set temp? It just takes a lot longer?

 

[jagec]

The air handlers with Ruud marked on them are all in the attic. Supposed to be a good name. Insulation... Its just the silver foil lined ducts running around but organized. Not traditionally insulated by that pink stuff if that's what you mean. How does capacity work so I can try to find out if it's enough to handle it? Total house sqft is 2700.

How cold should it be at the vent? Too cold to keep a hand there for longer than a minute?

Separate question is if the doors are closed and rooms inside cooling, how does the thermostat out in the hallway accurately reach the set temp? It just takes a lot longer?

It's rated in tons. A house that size will probably need 4-5 tons of cooling, which is 48,000-60,000 BTU/hr. The model number on the compressor (the outside unit) usually has capacity coded into it in BTUs/hr...so there would be a "48" or "60" in the model number somewhere. Of course, with two units they might each be half that.

The vent air won't be so cold that you can't keep your hand over it. I just checked my vents with an IR thermometer, and they are in the mid-50s when blowing air. They cool the house down just fine. My vents also vary from room to room--it's nearly impossible to get perfectly balanced airflow unless you start fiddling with the vents individually.

Closing the doors will make the rooms cool down faster than the hall, but internal doors are far from airtight, and the thermostat in the hallway will reach the setpoint once enough cold air leaks out of the rooms.

You've checked the filters, right? If they are clogged up, it could explain your airflow and lack of cooling. They should be replaced every 3 months or so.

 

[ManBearPig]

We take pretty crappy care of our AC unit/filters/etc, have an older house and older unit, and its perfect. If our system was like yours I'd go fucking nuts, especially if it's new! Call those assholes up and tell them to fix it. That's absurd. FOUR hours and only a 3 degree drop? Takes like 15 mins here.

 

[richardycc]

my house has a similar setup, except my first floor air handler is in the basement, and we have this same issue when it's 95+ degree outside if I don't turn on the AC for the first floor ( I ususally just run the 2nd floor unit as all the bedrooms are on the 2nd floor). I think the problem is a combination of 1. the days of oversizing a system are over, CACs operate more efficiently the longer they run continuously, and should be sized so they don't turn on and off frequently on hot days. So in order to cool your house to a comfortable temp, you should run both units all day long and let them stop on their own. 2. the air handler in the attic doesn't help either, it's probably over 150degree up there, so the cool air is few degrees higher, and looks like you are not using the unit on the 2nd floor. Since they designed the 2 units to run together as a system to cool your whole house, running just one unit can't cool your house adequately. just my 2 cents.

 

[skull]

The air handlers with Ruud marked on them are all in the attic. Supposed to be a good name. Insulation... Its just the silver foil lined ducts running around but organized. Not traditionally insulated by that pink stuff if that's what you mean. How does capacity work so I can try to find out if it's enough to handle it? Total house sqft is 2700.

How cold should it be at the vent? Too cold to keep a hand there for longer than a minute?

We're using the 2nd floor only right now at bedtime and its doing it's job but it's not open like the 1st floor is. But anyway the vent down in my office does nearly nothing when I close the door. Can't feel the air blowing when standing under it, only up at the vent. Trying to determine if it's the temp or airflow or both.

Separate question is if the doors are closed and rooms inside cooling, how does the thermostat out in the hallway accurately reach the set temp? It just takes a lot longer?

Sounds like the ducts not being insulated in the attic are the problem. One of our houses has insulated but not very well ducts in an the attic and the system can't keep up in the high 90s because of it. The vents shouldn't blow out more than 24 degrees colder then the air going in. Around 14 to 20 is better. One way to find out if its the uninsulated ducts is to take the temperature difference at the air handler. If you have a nice 20 degree split right at the unit and a 10 degree difference at the vents theres your problem.

 

[CPA]

Do you have large windows that don't have blinds/shades on them? Have you had the windows and doors inspected for air leaks? Are your filters clean? Check your intake ducts, do they have holes in them (Mine did)? If they do, your intakes may not be pulling hot air out of the rooms well enough.

 

[Dallascisco]

You likely have an underpowered system or they need a recharge.

 

[GT1999]

I really don't know much about AC, but that just doesn't sound right. 1500 sq ft on a floor is definitely a lot but I've heard/seen much worse and it cools just fine.

Get a second opinion/company to inspect your system?

 

[Genx87]

This year I have been going through AC hell. My house has mice that chewed through the wiring on the compressor unit. My GFs kick starter crapped the bed when it was a weeks worth of 90s. And my dads two condo's both failed in Florida. So I have learned a little about AC units this summer.

What you describe sounds a lot like what happened at my house. The AC would run for hours and drop the temp 1-3 degree's. Are you shutting vents in an attempt to move more air to other rooms? After talking with the AC repair guy he made a suggestion that you leave all vents open and run the fan to circulate the air. By completely closing vents it will reduce airflow over the S-coil which can cause it to freeze up and not cool the air as efficiently, or at all. He determined the issue when he tested the line coming back was below freezing. It was supposed to be 34ish degrees but was reading 27. After opening up all my vents it returned above freezing.

I would close the vents downstairs in the summer. Makes sense right? Why cool the basement? Well it was causing the system to not work properly. My tenant has followed these instructions and it works just fine now.

My dads house(8000 sq feet) has two units. I believe they are both 5 ton units. They need to both run in order to cool the house. I have the hardest time convincing my dad of this lol. Same with his dual furnaces. He doesnt want to spend the money. I cant blame him though.

 

[Brovane]

We had a new system (with 2 units outside serving each floor) put in last year along with the dormer and some vents are blowing out more than others. We had them come back at one point to try and adjust that and they did something in the attic where the ducts are and just said "see how it works out now". Well it's been pretty much the same thing - we really don't complain except when we actually need it like days like today when it's 95F outside.

The system for the 1st floor has been on for 2 hours now and it's still hot at 83F inside according to the thermostat and we have it set to the mid-70s - not likely it will reach that - it was like 85F when we turned it on so it's barely done anything. The system upstairs is off but we closed all the 2nd floor doors. There's about 1500sqft of lateral space for the 1st floor plus the stairway up to the hallway of the 2nd floor (where the return with that large filter is).

Is it normal for a central A/C system not be able to make the area (1st floor) so cold that we'd have to turn it down? 83F is barely bearable.
Is it possible to recirculate to specific vents in the house if some are barely getting any air through?
Is there just 1 setting for the amount the entire system blows out? Recirculating that would make other areas warmer.
Is it a freon issue - we've hardly used it since new but maybe it was never rightly charged.

This sounds like the problem my in-laws had. They lived in Bakersfield and there house was always room during the summer. The rooms closes to the air handler where freezing but the further away you got the vents dropped off so there was no air coming out. I told my mother-in-law to have somebody go up in the attic and check the vents several times. Somebody finally went up there and one of the vents the duct work had come off the vent and was 5-feet back from the vent. So it was just blowing out in the attic.

 

[rh71]

All the vents are wide open. We have blinds on all windows and the windows are not leaking from what we can tell from winter.

I just checked the air handlers and the ducts in the attic... the ducts are all very well insulated and in good working shape. Unfortunately there are no visible valve handle adjusters on any of them.

EACH air handler (1 for each floor) is this one: http://www.amazon.com/RHSL-HM3617AA-.../dp/B0080R7HPG which says 36000 BTU

The outside units are each this one: http://www.routeac.com/2-5-ton-rheem-13-seer-cooling-only-condenser-r22-rand-series.html which says 30,000 BTU and since you mentioned it should be half of the 36000/48000, capacity seems ok.

Some pics:
http://pics.bbzzdd.com/users/rh71/IMG_20120622_090221.jpg (1st fl handler)
http://pics.bbzzdd.com/users/rh71/IMG_20120622_090739.jpg (2nd fl handler)
http://pics.bbzzdd.com/users/rh71/IMG_20120622_090749.jpg (duct work)
http://pics.bbzzdd.com/users/rh71/IMG_20120622_090407.jpg (air handler label)
http://pics.bbzzdd.com/users/rh71/IMG_20120622_091444.jpg (outside unit)

Is there any truth to having both floors running at the same time and all doors open making CAC cooling more effective?

 

[SS Trooper]

Would anyone mind to comment on what a ball park for a CAC system for single story(with a basement). 6 rooms total. I'm hearing 2-2.5k since I have existing duct work for heat. Any input is much appreciated.

 

[SirStev0]

is awesome. (my only contribution)

 

[bignateyk]

It's possible they just did a terrible job laying the duct-work. There are alot of mathmatical calculations that go into how to size the ductwork properly and how to reduce the size every time you branch based on several factors.

If they didn't properly size and step-down the size of the ductwork as they laid it, you'll end up with some vents blowing out way more air than others regardless of whether or not they sized the actual compressor right.

 

[Markbnj]

All the vents are wide open. We have blinds on all windows and the windows are not leaking from what we can tell from winter.

I just checked the air handlers and the ducts in the attic... the ducts are all very well insulated and in good working shape. Unfortunately there are no visible valve handle adjusters on any of them.

EACH air handler (1 for each floor) is this one: http://www.amazon.com/RHSL-HM3617AA-.../dp/B0080R7HPG which says 36000 BTU

The outside units are each this one: http://www.routeac.com/2-5-ton-rheem-13-seer-cooling-only-condenser-r22-rand-series.html which says 30,000 BTU and since you mentioned it should be half of the 36000/48000, capacity seems ok.

Some pics:
http://pics.bbzzdd.com/users/rh71/IMG_20120622_090221.jpg (1st fl handler)
http://pics.bbzzdd.com/users/rh71/IMG_20120622_090739.jpg (2nd fl handler)
http://pics.bbzzdd.com/users/rh71/IMG_20120622_090749.jpg (duct work)
http://pics.bbzzdd.com/users/rh71/IMG_20120622_090407.jpg (air handler label)
http://pics.bbzzdd.com/users/rh71/IMG_20120622_091444.jpg (outside unit)

Is there any truth to having both floors running at the same time and all doors open making CAC cooling more effective?

Well, all A/C systems are circulating. Cold air comes out the vents, and warm air goes back through the warm air return. Whether you need the doors open depends on how yours is set up. If it was put in when the house was built then you may have warm air returns in each room. If that's the case then you don't need to worry about the doors. If it's a retrofit or they were looking to save money then you may have a single large warm air return in the middle of the ceiling in an upstairs hall, relatively near the air handlers. In that case leaving the doors open will help warm air recirculate back to the handlers.

But, in either case a properly functioning system would still cool those rooms down. Most interior doors aren't sealed anywhere near well enough to cut off airflow.

A/C systems are dead simple, and there really isn't that much to check. You've got good insulation on the ducts, a clean filter on the return, sufficient cooling capacity, enough refrigerant, and properly functioning thermostats and that house should cool down. The system sounded new, so I doubt you have filter or refrigerant issues. If refrigerant is low you should see some signs of icing (like the frost in an old-fashioned freezer) on the lines running from the outside compressors to the air handlers. If you don't see any of that you likely don't have a refrigerant issue.

Beyond that, it's time to get the thing looked at by a professional. Sizing capacity is very important. If the capacity is too low you'll see exactly what you're seeing: the system will run constantly without having the desired affect. Eventually the compressors will start to fail from constant duty. As a point of comparison, we have about 2800 square feet on two floors, and 5 tons of capacity. If we return from a summer vacation to find the house at 85-90 degrees, the system will have it down to 74 degrees inside of 60 minutes, and then shut off. If you aren't getting the same level of performance the system simply isn't working.

 

[rh71]

I'm actually on the phone with the company now and they say that playing this catch up game with the temps will result in quite a few hours before it cools down (I know that's contrary to what's been said) and it's also not good for the electric bill. They also said since temps inside did drop it means it's cooling. They're going to come balance out the vents though, but they advise me to leave the AC on all the time but adjust temps as need be on each floor. I've opened all the doors up there too as there's just the single large return on the 2nd floor hallway ceiling. The entire 2nd floor and all A/C work is new from last March. It sounds like having a warm air return on the 1st floor would have been a big help? I heard the filter on the return should be 6 months? But since we barely used it last summer I don't think it would need a change.

Vents & doors everywhere all open right now - I'll see what happens over the course of the day or two.

 

[GT1999]

I'm actually on the phone with the company now and they say that playing this catch up game with the temps will result in quite a few hours before it cools down (contrary to what's been said) and it's also not good for the electric bill. They're going to come balance out the vents though, but they advise me to leave the AC on all the time but adjust temps as need be on each floor. I've opened all the doors up there too as there's just the single large return on the 2nd floor hallway ceiling. I'll see what happens over the course of the day or two.

They're trying to cover their own ass. It takes 10-15 minutes to cool my ~900 sq ft apartment. I don't see why 1500 should take a whole lot longer...

 

[rh71]

They're trying to cover their own ass. It takes 10-15 minutes to cool my ~900 sq ft apartment. I don't see why 1500 should take a whole lot longer...

I edited the above... it sounds like having a warm air return on the 1st floor would have been a big help? All the warm air may not be getting sucked up to the 2nd floor hallway efficiently enough?

 

[GT1999]

I edited the above... it sounds like having a warm air return on the 1st floor would have been a big help? All the warm air may not be getting sucked up to the 2nd floor hallway efficiently enough?

I would think that's essential for proper circulation, but again I really don't know jack about AC and I'm not going to pretend to. I just have my AC at 70 F when I'm gone and 65 at night (both the woman and I like it frigid) and it can go from 80 down to 65 in 15 minutes but that's a rough guess. You can really start to feel it cool down. If our place was at 83 we would go nuts.

My AC bill ranges between $90 and $140 a month for only 900 sq ft though, so we pay for it.

If you think about a computer case, you have intake and outake fans. Why would AC be different?

 

[Hoober]

I edited the above... it sounds like having a warm air return on the 1st floor would have been a big help? All the warm air may not be getting sucked up to the 2nd floor hallway efficiently enough?

Yes, ideally you'd want a return on both floors. I think it's interesting that there's a return on the 2nd, but not the first. Usually it's the other way around.

To address their statement about the cooling speed -- I have a system similar to yours, but instead of two separate handlers, we have 1 handler and dampers to send air to the correct floor depending on what the thermostats are demanding. The house is approx. 2700 sq. ft., and we have a 4 ton heat pump.

If we turn off the A/C during the day and turn it back on at night, when we get home from work, it takes a little under an hour for the system to drop the temperature 1 degree. The outside temperature today is supposed to approach 100. My wife and kids will be home, and so we'll leave the A/C on all day. I expect the system to be running pretty much constantly to keep the upstairs near the set temperature of 76 degrees.