[Dalsaram]

I've had this issue for years now and I need some help or guidance.

My A/C does blow cold air but will not cool down the house less than 78. It's very hard to cool below 80. A/C often stops at 80 when it was set for 78 or lower and restarts. I set thermostat to 82 till 7:30 PM and 78 for the rest of the night

From supply to return, the temp difference is mostly 16-20 degree on any conditions. Two techs I called said my unit is working just fine since I do have the good temp difference and air flow was good. ( nobody checked with gauge though) . One said it's just undersized. However, I didn't have this issue before I replaced this unit. It's been a problem since the installation of the unit but I have been believing that the original HVAC company said everything is per the spec and normal. The weather wasn't very hot for years like this year.

The outside unit is just two years old, Goodman 13 seer. 4 ton, GSX130481. I saw other post with the similar issue and did some reading. (11:45PM).

When outside temp is 94 degree with 45% humidity, condenser discharge temp is 108.. Temp split is 14

Indoor humidity is 50% with 80 return and 60 supply. I have two returns with 12 vents

The unit ran from 7PM to 12 PM to drop temp from 82-80.

I want to call another company not hoping to hear I don't have any issue..but the unit is running almost constantly and still not cooling down the house. This is for 2nd floor of about 1800sq. It was 102 ish today. I added extra insulation, vent and radiant barrier in the attic. I had very cool summer before regardless of outside temperature.

any ideas?

 

[dan sw fl]

4 Ton should certainly be adequate for the defined space
in a Normal, proper operating set-up.

... Are the ducts in a 140'F + attic until 8 PM?
... Is the duct insulation value R-4?

1 > Thermostat
2 > Air Flow
3 > Duct leakage
4 > House Sealed

1. Set at 76'F and leave it for at least a week
... the unit should get the upstairs to < 77'F by about 10 PM.

Is the t-stat 30 years old?

Is the t-stat close to a vent?
_ One may have to Relocate and/or Replace the t-stat due to the frequent restarts

.... When it's > 92'F outside, one should anticipate
.... that cooling from 80'F to 76'F
__. WILL Take > 4 hours.

2. Have the air flow measured accurately at the return.
... Have the Supply Air pressure and temperature measured accurately.
... Have the Return Air pressure and temperature measured accurately.

3. Have pressure tests performed on the duct work for each system to determine amount of leakage.

4. Blower door test may be necessary to determine amount of house leakage.

 

[Dalsaram]

1. I guess you are saying the temp difference is quite normal?. The air feels cool while I used to feel cold before this unit. I have no idea how the temp difference was before I have this unit. The one for downstairs has temp difference of 20-25 degree and I do feel cold when the unit is blowing air. ( I have two units)

Thermostat is probably 15-16 years old. Once it passes the temp, it runs al the way. It seems it stops after 1-1.5hr hour of run. Thermostat is quite close to the secon return but there is a door. (thermostat is in living and return is in the room. Vent is probably about 13 feet away.

2. I guess I will call a tech to measure air flow. I was hoping I could have some clue before I call someone this time.

3. Visually checked by techs. No leakage was found.

4. The house was sealed 3-4 years ago. I was told there is not much leakage to be concerned. Most of windows facing west/east/south are tinted

 

[2old2rock]

From your description, it sounds like a duct issue, but you haven't really given us much to go on.
Has anyone checked the static pressure?

 

[DOGBOY]

are you saying you have a 4 ton on 1800 sq. ft.? How hot is the attic getting? Did you have a new roof installed? and if so is it black or dark? If a new roof are there any openings in the roof to let hot air out? Attics can get up to and exceed 150 degrees. But then your temp split would not be 20 as you say it is.

as dan and 2old said probably air flow. What size was your old system and did it do the job?

 

[udarrell]

One said it's just undersized. (Shouldn't be) However, I didn't have this issue before I replaced this unit. It's been a problem since the installation of the unit but I have been believing that the original HVAC company said everything is per the spec and normal. The weather wasn't very hot for years like this year. The outside unit is just two years old, Goodman 13 seer. 4 ton, GSX130481.

Was the unit U replaced the same tonnage & how old was it?
At 450-sf per ton of cooling it should handle what would be a normal load; if the other unit handled it.

I looked up the data on your model condenser & at 95°F ambient 80°F & 50%RH indoors condenser temp-rise is 16.8°F; 20°F indoor split; apparently close to what you're getting, but we don't have all the numbers.

Are U sure there are no air-leaks in the supply ducts?
Check infiltration rates & insulation values.

Do a free load-calc on that top floor to see what Btuh of heat removal should get it to say 76°F & 50%RH.
http://www.loadcalc.net/

 

[Dalsaram]

Before I called someone again, I went up myself almost first time and looked around. After a while of staring my evaporator coil, I felt a little bit of air from one of the duct and here and there around the coil. I taped them up all.

You know what happened? my temp difference from supply to return is around 20-22 when attic temp is 105 and around 19-20 when the attic temp is 120-ish.

The house is cooling down quite quickly. It was 100 today and I don't have any issue.

I am not sure why two previous contractor couldn't find this simple issue while you could all point out the duct issue.

I like to thank you all and also want to apologize if this can be called DIY.

 

[Dalsaram]

just other things asked.

The roof was replaced three years ago with ridged vent. It's not dark, but gray color. I added insulation and radiant barrier. The attic temp with outside 100 and sun seems about 115-125. Without sun, it's around 110-115 with outside 100 ish.

The old system was 12 years old 4 ton carrier while new one is good man 4 ton ( I heard it's low end brand..?).

I believed what two a/c tech told me that duct and everything looked okay. Nobody measured air flow or anything. One guy did check the air. It appeared he used a piece of paper to feel the air from vent and supply. The other guy went up to the attic and I have no idea what he looked or did since I didn't follow. Both told me my system is normal. One said it's undersized and recommended to replace with 5 ton if I want.

I am quite comfortable with temp and the way it works now but if you think I still need to call someone to check, please let me know.

 

[udarrell]

Before I called someone again, I went up myself almost first time and looked around. After a while of staring my evaporator coil, I felt a little bit of air from one of the duct and here and there around the coil. I taped them up all.

You know what happened? my temp difference from supply to return is around 20-22 when attic temp is 105 and around 19-20 when the attic temp is 120-ish.

The house is cooling down quite quickly. It was 100 today and I don't have any issue.

I am not sure why two previous contractor couldn't find this simple issue while you could all point out the duct issue.

I like to thank you all and also want to apologize if this can be called DIY. NO; it's OKAY...

Far too many pay NO attention to indoor airflow or duct leaks.
I saw that happen with my brother's A/C add-on to an old Thermo pride belt-drive blower Oil furnace where airflow was so low & obvious it was unbelievable, & with numerous calls, nobody paid any attention to it since 2005 & it is still a horrible unaddressed problem that is threatening the compressor; saved so-far only by a TXV metering device.

The system is also very low on R-22 refrigerant; the compressor's days are numbered...

The roof was replaced three years ago with ridged vent. It's not dark, but gray color. I added insulation and radiant barrier. The attic temp with outside 100 and sun seems about 115-125. Without sun, it's around 110-115 with outside 100-ish.

The old system was 12 years old 4 ton Carrier while new one is good man (Goodman) 4 ton ( I heard it's low end brand..?). Don't believe everything you hear...they will do the job

I believed what two a/c techs told me that duct and everything looked okay. Nobody measured air flow or anything. One guy did check the air. It appeared he used a piece of paper to feel the air from vent and supply. The other guy went up to the attic and I have no idea what he looked at or did, since I didn't follow. Both told me my system is normal. One said it's undersized and recommended to replace with 5 ton if I want.

I am quite comfortable with temp and the way it works now but if you think I still need to call someone to check, please let me know.

This is why you have to learn more about what constitutes good service-work & installs; also HOW to use simple safe ways to check system performance.

Then if you do a Free LoadCalc you have a reference point of what your system ought to be doing. Click on my image to find in my posts the performance checks you can do...
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