A/C performing properly, maybe expecting too much?


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Old 05-28-10, 11:01 AM
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A/C performing properly, maybe expecting too much?

I have an 8 year old system, heil 80% handler, 10 EER 2.5 ton condenser.

House is also 8yrs old, 2000sq/ft bilevel, fully finished (1000sq/ft main level), 18" of cellulose in the attic, efficient windows/sidewalls.

Refridgerant level was checked and a minor amount added last summer (although we barely got ANY hot days last year). Condenser coils cleaned every few weeks and furnace filter is clean.

Thermostat is a Honeywell RTH230b set to a CPH of 3, fan speed in air handler set to HIGH (black wire) for cooling.

With an ambient temperature of 90f I set the thermostat to 72f and it will get there, providing a measured temp drop of 19-20f every time between supply and return, but it runs almost constantly to maintain it in the house... not much cycling.

Is this normal? It may be given all the variables, but it will get very very expensive since the system eats about 3000 watts in operation!
 
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Old 05-28-10, 11:53 AM
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No expert...but it might be that your unit is undersized. Has it always done this?

A/C is most efficient when it runs long....short cycles are real bad. Continuous in a residential environment would seem to indicate a problem though.

I had that issue in my last house and a simple thermostat replacement made my comfort level much higher...and lowered my electric bill by almost 20%.

What kind of stat do you have? What is the temp swing? I mean..does it go up 3 degrees before the A/C kicks on?
 
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Old 05-28-10, 02:03 PM
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I'm certainly no expert in this area, but I don't think there is much wrong with your system. I would consider temperatures above 90F to be at the maximum design temperature for your system. That means it was designed to operate at full capacity when the outside air temp was somewhere over 90F. If you are able to maintain temperature inside under these conditions, I would say it is ok.

My system runs constantly during those temps and my inside temp will rise, but my system is undersized/in a poorly insulated house.
 
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Old 05-28-10, 02:51 PM
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Raise the temp to 75, and see if would make the system cycle.
 
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Old 05-28-10, 04:11 PM
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With an outside temp of 90 the unit should run all day. If it cycled Id say you have an issue! So sounds like it is running fine! Gun is that a better post?
 
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Old 05-28-10, 05:42 PM
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lol.Airman.....I'll start keeping my mouth shut...sorry about the other one.

I still don't think it's right though. I'd recommend a checkup by a reputable company. Talk to neighbors and friends.

My 3 1/2 ton (1700 sf house) doesn't run all day even in 105-110 degree weather...and my 3 ton back in VA (2200 SF house) didn't either. Though...I never set it as low as 72.

We need more info on swing.

I know..I may be way off track...but it just doesn't sound right....
 
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Old 05-30-10, 02:52 PM
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Originally Posted by ls3c6
With an ambient temperature of 90f I set the thermostat to 72f and it will get there, providing a measured temp drop of 19-20f every time between supply and return, but it runs almost constantly to maintain it in the house... not much cycling.
That is all we need right there. Sounds excellent. You have heat getting in from somewhere, but it don't sound like it is from the attic, if 18 inches of cellulose, which is excellent insulation if blown in properly loose, and not trampled down.

It sounds like you are a thinking guy, and would know enough about drawing the blinds, not running vents needlesly, closing fireplace damper if applicable, etc.
 
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Old 05-30-10, 03:49 PM
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I made a boo-boo. My last post..I was thinking of a different thread. Sorry bout that.

I agree with everything said. now that I re-read.

I apoligize.....
 
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Old 06-18-10, 01:44 PM
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My honeywell stat doesn't activate by swing persay, but by cycles per hour... now if within that cycle the temp is i *believe* .5f away from the set point, but not a full degree off.. it will activate and it checks based on a 60 minute schedule (every 20 mins if CPH is set 3, 15 mins if set 4 etc)

yes all windows have blackout/thermal drapes, temp drop is good and I guess it's probably performing as it should.... my wallet just doesn't like seeing the electricity meter spinning +3000w so frequently.

It will cycle and run much less if I set 74-75f, but that's too warm for me... i'm an office guy so i'm used to office spaces that you can hang meat in while you work.

I have cleaned the condenser coils with garden hose water, but no chemicals... they look a little oxidized but generally clean, do i need to buy some of that foaming stuff from home depot?
 
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Old 06-18-10, 08:27 PM
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i am in the texas gulf coast area-20 miles inland.
very humid-today was 96 at 2 pm.
have about 8" fiberglas ins in the attic
1100 sq ft house on slab/ 1/2 out side walls (2x4) framing -is insulated- 6 out of 7 windows are high effencent.
3 ton ( 1996) r22 system
t-stat- 74-night time/9 am 77.
2-3-4 pm comp 'on' 12 minuits/ 21 minuits 'off'
 
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Old 06-19-10, 07:58 AM
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There is no 'expecting too much'. It all depends on what you want. If AC performs normal, but it won't stop, another word it can not get to the set temperature so it won't stop. there are only two issues here. 1. Heat leaks in from some where, or not enough insulation. 2. The AC system is too small. The way to check this is: During a normal day, turn your AC off until room temp reach say 80, then turn your AC on by set t-stat to 72, and watch how fast your room temperatue goes down. Takes how long from 80 to 79, and then to 78... you will see every period is different, and getting longer when the temp getting lower. If the period longer than 5 minutes at high end, or 15 minutes at low end, you need to work on the above either 1. or 2. or both (adjust the other way accordingly if the period is too short). Based on what you want, you can pretty much design or control the cycle time.
 

Last edited by clocert; 06-19-10 at 08:19 AM.
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Old 06-19-10, 09:55 AM
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Grand Rapids summer design temp = 88.
 
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Old 06-19-10, 11:54 PM
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This subject always amazes me, always more to learn. I feel clocert is correct in the cooldown measurement and if the OP's problem is it runs constant currently, its gonna run evn longer under the 80 down to 72 scenario. IMO his insulation is fine. He's knowledgeable enough to know if he's got major air leaks. I feel his unit is undersized because his lifestyle undoubtedly doesn't meet the design criteria. Asking for 72 degrees in the Summer is on the verge of absurd with all due respect. If shooting for 72 and by running constantly, the humidity inside must be low, therefore it must be freezing inside. I get cold asking for 76. Dept of Enegy guidelines talk about 78-80. The operating issue is one issue, the electrical consumption is a separate one. EER 10 is getting dated. A 12 is more the std now. Electrical rates go up, getting more efficient is called for.
 
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Old 06-24-10, 01:18 PM
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So I can't expect anywhere near the frigid you get in offices, grocery stores or my cars?

I've been collecting data the last few days and I usually see 16-18 degrees below room temp from the vents... but i'm still not impressed with performance or it's ability to really cool the rooms.

Anything left to troubleshoot? I have never looked at the a-coil because the ducting there is screwed and aluminum taped to the air handler... I spose those need a good fin cleaning like the outdoor unit does?
 
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Old 06-24-10, 03:33 PM
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With 18 degree split and good insulation all around, I just don't understand why can't you get the temp down to 72. The only thing you did not mention is how strong the air blow from the vent. Can you feel the cold air blow to your face from 8 feet away (from at least one of your registers) ? Most DIY people don't have tool to measure the air volumn, but just for your info, the number should be at least 1000 cfm.
 
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Old 06-25-10, 12:57 AM
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Car systems are designed to cool you off quick when you get into a hot car, unlike home systems.
 
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Old 06-26-10, 01:38 PM
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I just turned it on 1hr ago (3:30pm), it's sunny and 80f with 60% humidity... I had the windows open until then and the indoor temperature rose to 79f and fairly humid.

I have a 4 input digital thermometer on currently with 1 probe in the outlet air vent in the floor (plenty of velocity, drapes blow around) and another in the intake return vent which is in the center of the upstairs "great room" about 9ft in the center of the room (the room is 25x20' with 14' cathedral ceiling). This room has 3 4x10 outlet vents on the floor and one smaller one under the sink with 1 return. (outlets are on the outer walls, return is in the center of the room).

I'm showing a temperature differential of 17.4 degrees... 59.4 outlet, 76.8 return.

Thermostat has dropped from 79f to 76f in this hour.

The basement level is 71.9f with all the vents closed, but the return vents are not blocked down there.
 
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Old 06-26-10, 02:47 PM
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I think you are OK, may be that is all you get from an 8 year old 2.5 ton unit. with 17-18 split, strong air blow, get temp from 79 to 76 in 1 hour (remember when your system is constantly running, the air temp in your room only up and down 1 or 2 degrees, and in that situation, everything in your home, including wall, desk, floor, etc are still cold, at the set temp, or may be only half degree higher then the set temp. so the air temp will get to the set temp quicker.) based on what you have now, your cycle time should be 20-30 minutes which is fine by any standard)--the only thing worrys me is the outside temp is only 80, not a good day to test the unit. another word you won't know if your insulation is good enough or not. plus you get help from the basement returns.
 
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Old 06-26-10, 03:32 PM
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Now at 3hrs constantly running I'm down to 72-73 but not low enough for it to turn off and cycle, currently still sunny outside and 78f... All drapes closed
 
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Old 06-26-10, 06:08 PM
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Hmmm.

What is the humidity with the temperature of 73 degrees?
Also a lot of people make the mistake of opening the windows in the mornings when humidity is highest and then closing them and turning the ac on in the afternoon. Your ac also has to remove the humidity (moisture) out of your home along with dropping the temperature. If your temperature is 72 degrees and your humidity is 70 percent you are going to be uncomfortable. If your temperature is lets say 76 degrees and the humidity is in the 40-50 percent range you will be more comfortable. This is also how heat index is calculated. Heat index is the "feels like" temperature.
If your unit is running and the temp is 73 and the humidity is above 60 percent your unit has problems. Also you mentioned the indoor evaporator coil. If you keep constantly clean filters in it and get good airflow it should be ok. Do you see water coming out of the white pvc drain line outside while running? Just thinking out loud...
You may have other issues is coil freezing any at all inside? May be a little low on the ol' R-22.
If you have outside temp of 78 degrees there is no reason it shouldn't get down to 72 inside.
You can only expect a 20 degree temp difference between inside and out with a good efficient working unit.
Most units especially older ones it is more like 15 degrees. Lets say it is 97 outside you can not expect more than 20 degrees or 77.
I believe your unit may be slightly low on charge or your condenser is really dirty.
 

Last edited by martymartin; 06-26-10 at 06:16 PM. Reason: Wanted to add something...LOL!
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Old 06-26-10, 06:12 PM
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After 3hrs and it had reached 73 it is very comfortable, too cold for my gf... But it did take 3hrs to get there.

I always change the filter every 30 days and the drain line has a pretty steady drip to the floor drain during operation.

Maybe when I open the windows I let in too much humidity that takes hours to reduce? I like to leave the windows open until 80+f and 50+% humidity occurs, then I close them and turn on the a/c until It cools off at night again.
 
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Old 06-26-10, 06:22 PM
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That's goo85d...

Sounds like your charge is good as you said there is steady drip out of the drain. If charge was low you would not get that as indoor coil would be freezing up. I still say it is the humidity issue. 73 degrees with 50 percent humidity is great. Where at night you will have 73 degrees and 85-90 percent humidity outside. Most people think airconditioners cool only. They cool the air but more importantly they remove the moisture.
Glad it is working for you....
 
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Old 06-26-10, 11:18 PM
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So if it's working properly, do I need to get a 2nd job to pay for it? It seems to keep the humidity in check it needs to cycle a few times per hour once the set-point has been reached... with a 3000w draw and at .10/kwh it's going to add up quick.

At 8p I left so I turned it up to 78 from 72, when I returned at 1a it was 65 outside with 90% humidity... the house raised from 72 to 74 in that amount of time, but felt stuffy so I had to turn it back on down to 72.

But is the low temperatre with high humidity better and I should just open the windows?
 
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Old 06-27-10, 12:15 AM
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Interesting discovery, I removed the grille on the main room that has 4 outlet vents and 1 return, I found a 1/4" gap where the return isn't sealed... I could see the insulation from up above, I thought the return should be sealed to the room it's drawing air from and even though it was only 1/4" I sealed it anyway.

Here's pics of the room and the gap with the grill removed of that return, what do you guys think?

Room, 25x20x14', 4 outlets, 1 return... accounts for more than half of the upper level, thermostat located near the bedrooms in the hallways of the remaining 400sq/ft:



Behind grill of return in above pic, there are 3 returns on the upper level all have good suction/vacuum, the other 2 do not have any gaps like this one, I sealed it with tape for now:



any thoughts?
 
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Old 06-27-10, 12:23 AM
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One other interesting discovery, I have 3 return vents on the upper level.

1 in each bedroom (14x14 and 13x9) and 1 in the main room which is 25x20x14, I removed the grilles from each and verified each has very good vacuum, however in the main room there was a 3/4" gap at the top where I could see the insulation from the attic in that gap... I sealed the gap off with masking tape for now and it seems to be drawing air from the room more aggressively.
 
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Old 06-27-10, 05:10 AM
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If you can not cool your house down with 18 split and strong airflow, the only problem I can think of is the house insulation. It is simple physics, you need to find out where the heat source is. A thermo gun may help to check all the walls, windows, doors, ceiling, etc... to see if there are any hot spots.
but with 56F and 90 Humidity outside, if your room temp is at 74 and is too humid, you may need a dehumidifier, not A/C.
 
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Old 06-27-10, 12:15 PM
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Fixing that gap in the return seems to have helped a ton, I feel the brisk cold air circulate through the large room now as its drawn from the return
 
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Old 06-27-10, 07:33 PM
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It is a rare contractor that actually does proper duct sealing it takes a lot of time and you have to be meticulous. Residential work is way to competitive for that kind of thing. If you had gaps at the returns you probably have a LOT of leaks in your system. I just did a total replacement of my supply duct in my crawlspace I was amazed at how poorly the ductwork was sealed it was shameful and had been like that since 1971. My unit is now oversized and only runs a few minutes then off for a while even at 100f ambient temps.
 
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Old 06-28-10, 10:24 PM
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You're on the right track...

Originally Posted by ls3c6
Fixing that gap in the return seems to have helped a ton, I feel the brisk cold air circulate through the large room now as its drawn from the return
Yep, that will help. I would go over all of it with a fine tooth comb. If you are sucking air from attic, crawlspace, etc. that will definitely affect your units operation.
Like clocert said there is leakage and once you get that stopped your unit will run less and put out more airflow.
 
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Old 06-29-10, 05:16 AM
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Don't underestimate the coil!

This is an annoying one for me because unless the coil is completely filthy, I can't even tell if it needs to be cleaned! A microscopic layer of dust insulates the cold metal like a blanket, which makes the air blow longer to cool a room, which makes more dust blow through the coil, making it even dirtier and insulate even more. Eventually the layman is able to see that it's dirty, but that's probably when the unit doesn't cool at all. When I read about this conundrum on this AC blog, I got a little brush for my shop vac and go at the coil about once a month. My unit's about twenty years old and still works *okay*.
 
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Old 07-04-10, 03:30 PM
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As an update, I turned it on last night around 1am when humidity/temperatre was rising after having the windows open for a few mild days. It was 78f/80% humidity outside at this time.

The house was 80f when I started the a/c and checked delta-t after 15 minutes.

Humidity was mild to high in the house and I saw a 13-14 delta-t at this time with the stat set @ 72f.

I went to bed and woke up with the house stabalized at 72f, ambient outside temp of 88f and 50% humidity.

The unit cycles on/off every 10-15 minutes and runs for a few minutes to maintain this. Around 5pm I decreased the stat to 70f and checked delta-t at the main level of the house outlet and return vents, I am running at 18f of split right now 53.6 out of the vents and returning 71.5 through the return.

Also keep in mind, I have returns/vents in the basement, all the outlet vents are closed but the returns are not... should I be leaving those vents open or closed as I have them?

I removed the tape around the manifold to look at the a-coil and it looks clean so not messing with that.

The decrease from 72 to 70 has had the unit running constantly since 5p and while the stat is reading 70 it is still on.

All is well?
 
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Old 07-05-10, 02:25 AM
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Looking good, and feeling good.
 
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Old 07-11-10, 12:41 PM
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So do I want to leave the downstairs/basement OUTLET vents closed? I'm trying them open right now and it doesn't seem to reduce velocity to the upstairs vents much, there are also 3 return vents in the basement which i've never blocked.
 
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Old 07-20-10, 07:14 AM
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Originally Posted by ls3c6
So do I want to leave the downstairs/basement OUTLET vents closed? I'm trying them open right now and it doesn't seem to reduce velocity to the upstairs vents much, there are also 3 return vents in the basement which i've never blocked.
Unless the basement is a living area, I'd try closing both supply & return air during the cooling season & see what the effect is.

You have to view the inlet air side of the evaporator to see any lint build-up, &/or shine a light through it.

Seal around the supply vents too.
Also, seal as much air infiltration as possible.
 
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Old 07-27-10, 11:06 AM
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Originally Posted by HVAC RETIRED
Unless the basement is a living area, I'd try closing both supply & return air during the cooling season & see what the effect is.

You have to view the inlet air side of the evaporator to see any lint build-up, &/or shine a light through it.

Seal around the supply vents too.
Also, seal as much air infiltration as possible.
It's a bilevel/raised ranch house, the basement is fully finished (1000sq/ft) and living space with egress windows with it's own supply and outlet vents, i have the outlet vents closed now because it seems to stay cold down there on it's own.

I also put one of those "cheap" filters in and noticed it did improve velocity, the ac is a 2.5 ton and consumes about 2900w while running and with probably 400-500 of that being the blower.

I routinely see a ~18 degree split.

I think it cools well it's just that 3000watts really heats up the electric meter!
 
 

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