new home ac doesn't cool

[smp7015]

My house is a year old. The AC will not get the house below 80 in the middle of the day. With it being 95 degree's with a 53 % humidity outside.

Yesterday a tech came out and did some air balancing and checked the freon charge. It is still under warranty. Before the tech came out the house wouldn't cool bellow 82 degree's. The tech told me that the system was overcharged by 1 lb. I looked on the unit and it say's factory charge is 6.2 lbs. The tech said he removed 1 lb from the system. He seemed nice and helped explain alot of stuff. The temp on the line before he removed freon was 44 degree's. When he left I believe it was 61 or 62 degree's. He said the ideal is 60 degree's.

I recorded the temp today and at 3:22 it was 80 on the thermostat. It is 5:42 and it is still 80.

I have a carrier a/c model #38BRC030-321 SERIAL 0904E21623

The tech's diagnostics
S/A 57
R/A 77
SUCTION 73
HEAD 220
ODT 95
T-SAT SETTING 76

The home I live in is a Perry Home and is 1733 s.q. ft.
I know our a/c shouldn't have to run all day and not cool the house right. Plz help

[smp7015]

return air temp is 77 degree's

Air at the vents to room is 64 degree's

[ultratec]

I hope that the 030 in that model number doesnt mean 2 1/2 ton. looks like that machine is working. If its a 2 1/2 ton, its too small. Would like a liquid line temp reading

[Edited by ultratec on 06-22-2005 at 07:05 PM]

[ultratec]

You have a 7 deg. temp lose in the ducts, are they in a very hot attic and are they insulated? Hope its not a 2 1/2 ton..

[docholiday]

Yes I would want to know why your supply air is gaining so much from the outlet of the coil to the supply airregister also. That is a significant loss of capacity. The other numbers also agree with a high load or possible undersized unit but I wouldnt jump to that (undersized) conclusion until you find the reason for the duct losses. It may just do the job if you had 58-59 degree air going to the room.

It seems your ducts must run in the attic. Maybe your attic isnt ventilated well or the insulation is less than desireable for the ducts. Better have a look at that.

[smp7015]

The ducts are in the attic. The tech is coming tommorro again is there any questions I should ask. The reading on the vent which is farthest away from the unit (I looked at the duct in the attic to tell this) read 64. The reading closest to the unit is 62 degree's. The return air reading is

What is the ideal temperature to have in the attic on a 95 degree day? What should the unit be able to bring the house down too? I believe the tech told me that this unit was 2.5 ton's. He said Perry Homes sizes there unit's at the lowest possible. Is there any recourse I should try to have with Perry Homes? In the attic there are two square vents at the highest point. They are not powered and have no fins on them.

This is pretty crapy having a new house that won't get bellow 80 degree's in the summer time.

[uktra]

Do you have a return that goes into the attic? If so check for duct leakage. should also check supplies and air handler for leaks.

[smp7015]

Yes the return goes in the attic? I checked the duct for leakage, the supply lines, and the air handler. I felt a tiny bit of air movement where the return air goes into the a/c not much barely enough to feel. On the air handler there are a couple of small leaks like were some screw holes are and such. I have to say the job they did with the mastic on the duct is quit crapy. You can see black cracks where they didn't get a good seal.

Any suggestions on what I should have the tech do tommorro?

[smp7015]

What should the ideal temp difference be b/t the air entering the return air at the grill and the air exiting in a room at a vent?

[brian in mass]

Sounds to me like your duct insulation is too low ( r-factor), and is not sealed properly. Your unit paperwork should show what the plunem rise is (difference between the return air and supply air measured in plunems).

That is where I would start. Next have the tech check the actual sizing of the duct work and the amount and placement of returns. Looking at T-stat placement is also a good idea.

Also, depending on things like geographical location and house specs it's hard to say, but it sounds like your system is undersized by about a ton or so.

[smp7015]

Since this is a Perry Home and the home buyer doesn't have a choice on what size ac there should be what would you recommend if the system's is too small?

From everyone's post I have gathered the following:
1.) System may not be large enough

2.) R-factor of duct may not be high enough (tonight when the attic cool's I will take readings at the vents again)

These are my main concern's:
1.) Why was the system overcharged by 1 lb and after it was corrected did it not make that much difference in preformance?

2.) Why is there a 2 degree difference in temp from vent closest to unit to vent farthest?

3.) It seem's if the return air is sucking hot air at the plenum that the total house cooling would be affected but it doesn't seem to have those "huge" airflow leaks?

4.) How much does attic ventilation and temperature play on cooling?

5.) What would you expect the normal reading to be at the vents in temp?

[dan sw fl]

Originally posted by smp7015
this is a Perry Home From everyone's post I have gathered the following:
1.) System may not be large enough
2.) R-factor of duct may not be high enough

These are my main concern's:

5. What would you expect the normal reading to be at the vents in temp?

Diffuser air temperature should be < 60'F under the stated conditions .. RA = 77'F.

IF diffuser outlet is > 60'F with 57'F SA, you may wish to investigate whether duct is R-6. Replacing some of the duct with R-8 and tinting some selected windows may improve the performance of the existing equipment.

.......
Do you have a lot of windows? ( > 320 S.F.)

Is there any tinting on the glass?

........
A/C seems to be only Marginally Undersized.
You may anticipate that the A/C may run for 6+ Hours Straight if it's 95'F outside and t-stat setpoint is 75'.

Best of luck.

[miami mike]

You need to have them take the supply and return temps at the unit.

Then have them take the temps at the registers.

If your return air is 77 at the grill ....but 84 at the unit, you have found the problem.

Are your neighbors having the same problems?

If not its probably not a sizing issue.(assuming similar homes)

I suspect your gaining heat in the duct work.....either on the supply or return side.

Good luck and remember to let us know what happens.

[ultratec]

I bet you when the tech said it was overcharged by 1 1b, it wasnt an exact figure, that 1 lb if it was, was just to get his readings correct. If the system was off for alittle while, the ducts would be hot giving a higher temp loose from the A/H to the air outlets. There is going to be some increase in temp when the ducts are in a hot location, from the time the air leaves the A/H to the time it exits the air outlets (7 deg is alot). The tech that came out was mostlikly from the installing contractor and is not going to say anything too negitive if the system was undersized. IMO, unless you have a very well insulated home and is some kinda energy eff home, and is sitting under a blanket, I usually (depends) use 400-450 sq ft per ton, sometimes 350 (they used about 700 Sq ft per ton) I am not a big resi guy, and would not be able to to a load calculation for you on the computer. I see your not going to get too much sleep over this. Bring in another HVAC company to help you out. The system may be able, w/ some very fine tweeking, to do alttle better, I dont think so though, it sounds some what small.

[hoozdis]

....the superheat or subcooling? Ive found noncondensibles in new homes many times. The builders will let their hack installers do start ups and they dont have a clue as to what they are doing. I had one tell me that if he has 70 suction pressure and 250 liquid pressure then he calls it good. Another thing I can tell you about new homes is that the attics are ALWAYS under ventilated. Im amazed at how these so called builders get by with this crap. Oh, and by the way, I bet they used an Allstyle plenum coil and I KNOW they didnt put a drier on the liquid line. Sorry if I sound so negative but I really hate home builders. I equate them with lawyers.

[Black Adder]

Can't comment on whether your system is undersized or not as have no way to see the house from here. Good attic ventilation is worth about 1/2 ton of A/C so if you think you need a bigger unit why not try putting a heat activated roof vent fan in the roof. If the ductwork is not adequatly insulated dropping the temperature in the attic by means of good ventilation will certainly go a long way towards lowering the temperature at the vents. I generally don't like to see temps in excess of 60 degrees at the registers. 54 or 55 would be a far better cooling temp. If things are set up correctly the system should be sized to pull the temp down to 75 degrees on a 90+ degree day. What is temperature during the hottest part of the day in your attic?

[brimo]

I think you said it was 53 % humidity - that can play a big role. Before you can cool the air you need to take the moiture out of the air...speculation...2.5 is a little small - I installed in my own house (1700 sq feet) a 3 ton - 600 sq feet per ton is what I go by - but in more humide areas I would go a little larger to handle the extra load. Do you have a programable stat - if so give the unit somemore run time to help it get an early start on the hot day.

Good luck

[smp7015]

Bought a digital themometer at walmart.
Duct is R-6

@ 9:42 pm temp at vent in room read 59*

@ 9:50 return air read 75.6

Thats a 16.6 degree drop.
-----------------------

Return air at plenum(drilling hole and sticking themometer inside) read 76.6

Plenum out (again drilling hole and sticking theometer inside) read 57.7

18.9 degree drop
--------------------------------
Temp in attic is 90*

Temp in house with digital themometer at thermostat is 76*


I need to remind everyone that these are the readings when the a/c actually cools at night

Now these are the readings when the a/c actually seems to cool.

I will get readings tommorro when it is HOT!!!

[smp7015]

here is the link for the floor plan to my house

http://www.perryhomes.com/inventory/...0%27+Homesites

just go there and click floor plan and tell me if you think my

2.5 ton carrier is undersized



Thanks for everyone's help. I appreciate it

[Black Adder]

What is the r value of the insulation in the attic and walls of your house. ie: 2x6 construction in the walls? R30 in the attic?