AC help please

[Fl_Richard]

I live in SW Florida and my AC is running continuously and will not maintain temperature. Looking for suggestions.

Here is what I have - American Standard 4 ton 15 SEER split system about 4 years old.
My house is 2100sqft under air 3BR 2 bath CBS construction built in 85 with a bunch of blown in fiberglass insulation in the ceiling and nothing in the walls.

The system is blowing cool air I measure it at 56 degrees at the coldest duct. (IR temp gun) and 76 at the return.

Is she doing all she can? (it's 94 outside)

 

[Tim Frank]

Re: AC help please

I live in SW Florida and my AC is running continuously and will not maintain temperature. Looking for suggestions.

Here is what I have - American Standard 4 ton 15 SEER split system about 4 years old.
My house is 2100sqft under air 3BR 2 bath CBS construction built in 85 with a bunch of blown in fiberglass insulation in the ceiling and nothing in the walls.

The system is blowing cool air I measure it at 56 degrees at the coldest duct. (IR temp gun) and 76 at the return.

Is she doing all she can? (it's 94 outside)

Have you cleaned the o/s coils? If they are dirty the efficiency goes way down.
How humid is it?
What is the inside temperature it will reach?

 

[Fl_Richard]

Re: AC help please

Right now 78, at night I can get it to 73, during the day it will creep up to 80 or 81 with 96 outside. Last night it was 78 at 9:30 this morning it was 74 at 7:00.

I haven't cleaned the outside coils but there is no debris in them . The compressor is on a slab and doesn't get much debris around it.
One thing that I was concerned about. In the old days the freon lies would always have a little hot one and a big cold one. My cold one is cooler than the hot one but not cold enough to sweat. The line-set is only about 10 feet long.

Humidity is always around 70-80%

 

[SS MAYFLOAT]

Re: AC help please

The condenser coil can look clean, but debris can be packed inside the fins. Best way to check is use a piece of paper and see if it sticks to the coil in all locations. If the paper will not stay, the coil can be clogged. Is the air coming out of the condenser hot or just warm or neither?

 

[mike243]

Re: AC help please

19-21 is a pretty normal temp drop,try cking the temp in the attic,most of the problems i have found is too much heat,a power vent can make a world of difference,also a clean condenser coil dont hurt either ,mike243

 

[Tim Frank]

Re: AC help please

Right now 78, at night I can get it to 73, during the day it will creep up to 80 or 81 with 96 outside. Last night it was 78 at 9:30 this morning it was 74 at 7:00.

I haven't cleaned the outside coils but there is no debris in them . The compressor is on a slab and doesn't get much debris around it.
One thing that I was concerned about. In the old days the freon lies would always have a little hot one and a big cold one. My cold one is cooler than the hot one but not cold enough to sweat. The line-set is only about 10 feet long.

Humidity is always around 70-80%

It's nor just debris, it can just be ....dirt!
Spray the coils down with your garden hose and use some dishwasher detergent as a cleaner.

And most important, were you in this house last year, and if so, how did the AC do?

 

[hrdwrkingacguy]

Re: AC help please

4 ton in a 2100 sq/ft house in a place that humid most of the year is to small in my opinion...Here in phoenix where the sense-able temperature is higher but the latent heat(humidity) is less it is to small for sure...Unless the house has really good windows, low sun exposure, and a lot of insulation I think it is just doing what it is supposed to do...

If you have access to suction line and liquid line temperature as well as pressures I could tell you if its working properly or not for sure...

 

[Fl_Richard]

Re: AC help please

Can I measure these temperatures with an IR temp gun?

Where would I measure them? At the Compressor or Air Handler?

I had this unit installed. I asked the HVAC salesman if a 5 ton would better server the space. Their answer is always "the unit will not run long enough to remove the humidity".

It has never worked stellar. My neighbor has an old 3 ton unit half the size of mine and his house is a meat locker... and it's 10 years old!

 

[Tim Frank]

Re: AC help please

Sounds like you need to get the salesman back and get him to organise getting it to work properly.

The other issues may be how well your place is insulated, and whether the ductwork is adequate and has ever been balanced.

 

[mike243]

Re: AC help please

1 ton per 600sq' here in Tn is plenty,the more humidity the longer the run time/more capacity needed.the moisture has to be removed in order to condition the air.the less moisture the less tonnage needed to compensate for it.having the unit balanced could be of a big help ,mike243

 

[smclear]

Re: AC help please

How long have you lived there? Has it ever performed well in these conditions? Sounds like an undersized system to me.

Where did you measure the 56 degrees? You said the coldest duct. Was it a duct, or the supply air register? If it was a duct, I'd suggest insulating the duct first. If it was at the register, which register? The first one off of the main? What about the furthest register from the unit? In all honesty, 56 degrees at the register is pretty good. 94 degree, humid air is a lot to overcome. Also, what about windows, how many on which walls (south, east, west, north)? How efficient are they? Any other possible infiltration? Do you have any shade on you house at any time? There's a lot to calculate to properly size an HVAC system.

 

[Jeepster04]

Re: AC help please

A 4 ton unit is plenty enough for a 2,100 sqft house. Im amazed that youre living in a house that was built in 1985 and doesnt have insulated walls! I would say that 4 ton unit it doing all it can to cool a house that is uninsulated in 96F heat. You can have the walls insulated with blown in insulation. They can drill holes in the top of the wall between each stud and blow it in.. Then patch the hole..

If youre really worried about it, you can have someone come out and check the line pressures on the high and low side. I would personally use someone that installs American Standard but if you know someone that would know what the line pressures should be on your unit that would be fine. That will tell you a lot about whats going on.

 

[Fl_Richard]

Re: AC help please

Well the house is CBS block construction with a 3/4" furring strip and plaster walls. I guess they assume the block has some insulating factor. Just in the last 5 years you see in new construction with a 1" foam insulation layer under the furring strips. My windows are old and leaky. I'm looking into getting them replaced this year with the 1500 fed rebate to assist. I have 10 windows and a single pane tripple sliding glass door thats about 10 feet wide. Do windows account for a large amount of heat gain? Most windows are on the north and south sides of the house.

Thank you all for your advice and suggestions.

 

[Tim Frank]

Re: AC help please

Insulated walls are a big help, but good ventilation in the attic is arguably more important.
Make sure that you have lots of vents and that they are unobstructed.
Not hard or expensive to add more.

Windows are certainly a major factor in solar gain, but you can add some retro-fit films that help a lot....again, relatively simple and cheap.

Also, where are the return duct outlets located and are there a reasonable number?

Your circulation may not be very efficient. A couple of ceiling fans....the big slow rev kind might help too.

You can use the manual system fan switch to run your fan 24/7 during the really hot stuff....that also helps.

 

[fat fanny]

Re: AC help please

Over the last 10 yrs my experience's have been in this case 1 blocked and or to small return vents, 2 dirty coils (use a citirus cleaner), 3 dirty and or restictive air filter, 4 unbalanced system and ducts that create static pressure (ducts installed to close or @ the end of duct runs)

 

[hrdwrkingacguy]

Re: AC help please

you can measure suction and liquid line temperatures at the compressor and right before the metering device...A IR isn't the best tool, but if you get it as close as possible like < 1/2" away the beam wont reflect away from the copper because of the curved surface...

4ton for 2100 sq/ft in Florida is wrong

 

[tswiczko]

Re: AC help please

Just got done doin a little reading


CBS=Composite building system, CAN have up to R-28 insulation factor on walls (doesn't mean yours does), mold, moisture, wind, water, termite proof

your home is probably pretty tight( not prone to fresh air infiltration )

get a thermometer and stick it in the duct IR measures surface temperature and can be inacurate especially on curved surfaces or if you are holding it at an angle.

also 20*f split across the indoor coil( if your measurements are correct is about all you can ask for out of your system If there is adequate air flow.

Back to the tight structure, you probably have a make up air system on your home that should bring in fresh UNCONDITIONED air into the home.
it can be passive (aduct going into the attic space usually) or active ( abox with a small fan that brings in air and filters it and dumps it into the building) to make up for air being removed (gas furnace, water heater, and exhaust fans bathroom, stove hood, dryer vent) if it is passive any time air moves out of the building air comes in through displacement so don't leave your bathroom or stove hood (if it vents outside) running when not necessary also make sure the dryer is vented properly(this can be as much as 30,000 btuh extra heat load not to mention the moisture when in operation)

active systems can be cotinuous, activated by pressure switch,(when static pressure in the building drops it comes on)this can be a source of hot air infiltration (do not shut these down or plug them they are necessary) if your new system was sized smaller than the old one this could be an issue if not accounted for(sorry I can't run a "J" manual for you without physically being there and measuring or have a set of prints for your home)

also physically go and look at the insulation in the attic if it is blown in it can settle or can be moved by any number of ways( critters people wind) and could be covering your soffit vents which will need addressed.

I don't know if this will solve your problem but are things that need to be looked at as well

you also said the unit was replaced last year I'm currious as to what size unit was in before this one.
sorry I was so longwinded

 

[Fl_Richard]

Re: AC help please

That CBS sounds great - here in Florida CBS=Concrete Block & Stucco. I wish my house was airtight. Makeup air is via leaks.. Built in 85 it leaks like a sieve. All the window gaskets are shot - I'm slowly replacing them with dual pane insulated impact glass. But the suckers are eeexxxxpensive.

Over the weekend i looked into the air-handler and found I have a four speed fan - running on high. I switched it to low and it seems to have helped. The suction line is now cold and sweating a bit, the liquid line is a bit warmer than ambient. The condenser is blowing hot air... Could this be the cause?

BTW - My line set is smaller-ish. The air handler has a 1 inch ish fitting squashed down to probably 3/4 and the liquid line is probably 3/8 - 5/16". It's only about 15 feet long.

The unit replaced an old SEER 9 4 ton Reem unit - It had always struggled too. Since then I've added 1' of blown in fiberglass insulation that seems to have done nothing...

My attic temp runs about 135 degrees... would an attic fan help? They claim 30% savings by cooling the attic.

I hope I'm not wandering too far off the original topic in this thread. I think we all agree my units doing what it should be doing; maybe I need to start looking to gain efficiency in other directions.

 

[Tim Frank]

Re: AC help please

My attic temp runs about 135 degrees... would an attic fan help? They claim 30% savings by cooling the attic.

I hope I'm not wandering too far off the original topic in this thread. I think we all agree my units doing what it should be doing; maybe I need to start looking to gain efficiency in other directions.

See my earlier post....lots of attic ventilation is a key item.
If you have enough, you won't need a fan. Idea is to have attic at same temp as outside...or as close as you can....135 deg is an oven.

Solar film on windows etc.
There are a number of comparatively inexpensive tweaks that you can do to improve efficiency.

Ceiling fans can be a bid assist....don't forget to reverse them seasonally.