A/C not cooling house during the summer


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Old 06-28-17, 03:04 PM
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A/C not cooling house during the summer

Hi everyone...I was hoping someone can help me! We have a 3 ton Goodman ac for appx 1868 Sq ft home in SW Fl. We keep our thermostat set at 75..during the "winter" it works perfectly...as soon as the summer heat comes...the temp will rise to 80 at times!! If it rains (or is really cloudy) the temperature stays where I keep the thermostat set at. My husband blew about 25 bags of insulation in our attic before summer...which hasn't helped! When the sun goes down...so does the temp. He checked the duct work ....and could not find any leaks. When we bought our home...we kept the temp at 78...so this wasn't an issue...when we replaced our unit we previously had a 2 ton...and that did not cool during the summer either. I have an appt next Monday for a tech to come out...we could really use some advice and opinions...I have a bad back and don't work...so we are on a budget.
Thank you in advance for any insight your may have!!
 
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Old 06-28-17, 03:29 PM
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You didn't say how old the system is. Has any maintenance ever been done on the system (condenser coils cleaned, evaporator coil cleaned)? Also, is the filter in the air handler clean (new)? How cold is the air coming out of the vents? Is there a sufficient volume of air? These kinds of questions should be answered before the experts here can begin to help you.
 
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Old 06-28-17, 04:15 PM
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I'm sorry...my unit will be 3 years in September. My husband has cleaned the coils..and the tech will be doing so when he comes..it has been a year. The filter is due to be changed this weekend...we change it once a month. As of right now I do not have a way to check the temperature coming out of the vent...but no during the heat of the day it doesn't seem to blow very hard. This was an issue with our 2 ton as well...we assumed it was due to the size of the unit.
 
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Old 06-28-17, 04:24 PM
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When you upsized a ton, what changes were made to the ductwork to handle the extra airflow?
With 3 tons, you'll need to move around 1200 CFM of air.
What's the sizing on the ductwork that attaches to the air handler? And is it flex, round or square?
 
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Old 06-28-17, 04:50 PM
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There were no changes made to the ductwork...there was an area that was damaged...so it was replaced. It's round & is insulated. We thought it was possibly the ductwork size...however we had this issue with the 2 ton and the same ductwork.
 
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Old 06-28-17, 05:16 PM
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The ductwork may have been undersized for 2 tons.
You can't toss in a bigger unit with no duct changes and expect it to function. What has happened now is you've paid for 3 tons but your unit isn't putting out 3 tons capacity. Wasted money buying bigger equipment.
Was a load calculation done to determine 3 tons was needed?
You need to move around 350-400 CFM per ton of capacity at around .05-.07 static.
What size are your ducts now? Round, flex or rectangular?
 
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Old 06-28-17, 05:59 PM
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To be honest...I can't remember if a load calc was done..all of the ductwork is round...I'm not sure of the size...however my husband just told me that there are different sizes for different areas of our house. Is that common??
 
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Old 06-28-17, 06:08 PM
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Yes, it's required to reduce size downstream to keep needed velocity and static.
Read here for unit sizing information-

http://efficientcomfort.net/assets/d...ty_Control.pdf

http://efficientcomfort.net/assets/d...ent_Sizing.pdf

http://efficientcomfort.net/assets/d...s_Properly.pdf

http://efficientcomfort.net/assets/d...ign_Issues.pdf

For 3 tons worth of air, you should have roughly the following size duct for the main trunk-
Flex-18"-20" so long as it's stretched tight and not kinked
Round metal-16"
There are a host of different size rectangular ducts that would support 1200 CFM. You'd have to give me your specific size to see.
 
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Old 06-28-17, 06:11 PM
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You can do your own version of manual j here for heat loss and gain. You need manual d for duct sizing and I don't know if a free version to give you.

HVAC Load Calculation - Maunualj - Whole House Loadcalc

What I'm getting at here, is bigger equipment is NOT better.
 
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Old 06-28-17, 06:18 PM
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You need to answer these 3 questions first: (1) what is the temperature of the cold air from register? (2) what is the room temperature at that time? (3) can you feel the cold air from 10 feet away from any of your registers ?
 
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Old 06-28-17, 07:00 PM
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I don't have anything currently to measure the temp..I will do my best to get out to purchase something so my husband can do so and I will post the results. Thanks!
 
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Old 06-28-17, 07:12 PM
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Thank you...our air conditioner actually quite so we purchased the 3 ton because we added a room 2 years later.
 
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Old 06-28-17, 07:36 PM
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The things you'll want to look for when your appointment comes on Monday are-
-Operating pressures
-operating superheat
-operating subcooling
-return and supply air temperature at air handler
-return and supply air temperature at diffusers
-operating CFM
-return and supply static pressure
 
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Old 07-04-17, 04:34 AM
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Tech came out

Well the tech came out...he suggested replacing the return vent ...it's 9 inches and wants to replace it with a 16 inch (3 ton he measured the vents with the exception of my bedroom (I have 2 big dogs I can't control by myself) and said that the CFM was 800 and should be 1200... does the remedy he suggested sound appropriate? He also did a dye test on the handler...those results will not be done until Friday..but said that our evaporator coil needs to be replaced (would the ductwork cause this) ...but the coil is on backorder for 30 days!!!
Thx in advance for everyone's help!
 
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Old 07-04-17, 08:18 AM
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9" return air? heh, that's too small fora 1.5 ton.

I know an 8" is good for 150 to 200 cfm, 9" would be a little more and a 1.5 ton needs 600 cfm.

Was the airflow measured? if you only have one 9" return no way would it move even 800 cfm.

The 3 ton needs 1200 cfm; here's a duct calculator - Residential Air Duct Calculator - EfficientComfort.net

Even at the highest pressure drop used (which shouldn't be used), 1200 cfm needs 18" if using flex. and likely closer to 20" to actually work right.

Supply ducts probably undersized too.

Without the results of leak test no way to know if there's a leak.

If the airflow is totally off, impossible to tell if the charge is right, and a it's easy to misdiagnose low airflow as low refrigerant if the superheat isn't checked. (both low airflow and low refrigerant cause low pressures)

Going from 2 to 3 ton was a huge mistake; says a lot, evidently a lot of uneducated, unskilled people working in the trades with no grasp of theory.

there are people who think it's like dealing with a fridge or television and that you can "just put a bigger one" at will.

No, the machine is only a part of a complex system and everything has to match.
 
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Old 07-05-17, 06:47 AM
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one 16inch flex duct is still not enough air for a 3 ton. you will need at least 2
 
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Old 07-10-17, 09:33 AM
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Another ? If you all don't mind... it was the supply duct that was changed to a 16 inch...we have 4 return ducts ..it was determined that we are 1/2 lb low on freon so an evaporator coil was ordered (Goodman...yes they do suck...there was a 30 day backlog ...I called to complain and it should be here this week). Our house does cool down faster now that they supply duct was put in...but the temperature continues to rise from 12-6 like clockwork. Would a small leak in the evaporator coil cause this? We are now thinking of having tint installed...our neighbors have the same issue.
 
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Old 07-10-17, 09:58 AM
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16" flex is not big enough for 3 tons.
Incorrect charge as a result of the leak would create problems keeping up.
 
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Old 07-10-17, 01:57 PM
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You went from a 2-Ton to a 3-Ton, the duct system may not even have adequately supported a 2-Ton system. Low airflow destroys Btu/hr performance.

The contractors that have checked a 1.5-ton system near me since 2005 have never checked the airflow or paid any attention to airflow or the low condenser discharge air temp.

Also, unit is still low on R-22 charge so enthalpy change is about 5.7 change X 4.45 X only 375-CFM = only 9,512-Btu/hr. It has a TXV metering device or the compressor would have been destroyed long time ago.

With a proper charge & airflow: 6.8 enthalpy change X 4.45 X 600 = 18,156-Btuh.

Correct Airflow plus a correct charge makes a world of performance difference.
Going up to 3-Ton won't help if airflow is way low; also the charge will not be right.

When will the contractor's techs lean to check airflow first...!(?)
 
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Old 07-10-17, 07:46 PM
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"When will the contractor's techs lean to check airflow first...!(?)"

^They won't. ever.

These aren't the best quality people going into the trades. the good ones all go for some 4 year degree and rack of student debt.
 
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Old 08-14-17, 10:32 AM
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AC doesn't cool our home during the summer months

I posted awhile back and am continuing to look for answers. We have a 1868 sq ft home in SW FL. During from appx mid Sept-April our home is comforable...during the summer months it's miserable. The builder put in a 2 ton ac..4 years ago we replaced the unit with a 3 ton ...the 2 ton was done. We have had this issue with both units...beginning around 11:30 am the temp rises from 75 to 76...then continues up to 79 or 80 depending on how hot it is. Back in July we had a company come out ...the evaporator coil was replaced and the supply line was replaced with a a 16 inch duct...and we are still having the same problem!! However when it rains or if it's overcast...the unit stays at the set temp of 75. I am truly at my wits end...we have spent a lot of money with no results. My husband did blow insulation into our attic in May...however I am thinking there still isn't enough...I don't know what else it can be. I truly appreciate any input anyone can offer...our air does have a 17 degree differential.
 
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Old 08-14-17, 11:33 AM
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Threads combined. When you ask the same question.... the same questions get asked again from us. Better not to waste everyone's times by starting all over.
 
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Old 08-14-17, 12:09 PM
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OK,
The supply duct needs to be 16in if metal and 18in if flex.
The return needs to be 18 in if metal and a 16in and a 12in or two 14in flex.

If the unit can't move the amount of air to the rooms that is needed then you will never get it cool.
Please stop chasing this issue tell a heat load has been done.
 
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Old 08-14-17, 12:14 PM
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Insulation will do nothing to stop radiant heat. That is what is heating your home up. Please have a heat load manual J done. With out this it is a guess. Guessing has been costing you money.
 
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Old 08-15-17, 02:48 AM
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I don't know much about AC and getting ready to do a new AC install in SW Florida. So reading what I can and came across this, I see no one mention tightness of house.

4 years ago when I bought my current 25 year old SW Florida home. The windows were an awning type. 3 out 7 were so loose I had to screw them shut and tape the gaps.

The sliding patio pocket door (both panels slide) had no weather stripping, none. The front door and inside door to the garage had no weather stripping and large gaps.

The duct work was in good condition and I only had to seal a bit of leakage. Now from reading on the net I suspect a 2.5 ton ac was added to 2 ton duct work to cool the house.

The AC was attempting to cool the yard, with the cost of electric I found it hard to believe that no one had attempted to do anything.

I knew the windows and door were bad when I purchased house and planned on replacing them.

Perhaps these people are in the same situation and no amount of tweaking the system will help?
 
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Old 08-15-17, 07:42 AM
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Good point. if you don't seal the house right, AC is just a waste. Anyway, I guess we do not even mention this type of problems is because this is an AC forum, not a house building forum. We try to fix your AC, not your house. We do tell people to insulate the house, but we assume that they already know they must close/seal their windows and doors tight in order for AC to work.
 
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Old 08-16-17, 06:00 AM
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If I had not bought this house I would not have thought of it either! The couple I bought it from had their own business and were seldom home, so may not have noticed, but their electric bills must have been outrageous.
 
 

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