Air Conditioning - New House AC Problem

This seems like a nightmare. A friend that does A/C told me that I needed a 2.5t unit for a house I just finished renovating. Its a New Orleans single shotgun style off the ground with T&Grove floors. 1000sq' with 10' ceilings. I insulated the walls and attic very well. I still plan to spray foam under floors but I dont think that will make a big difference to fix this problem. When we went to get the unit the guy at the supply double checked and agreed that 2.5 was the way to go. Unit was installed a couple weeks ago and the house has not seen temp under 82 degrees. The split between return is around 17. Copper sweats outside. The unit never shuts off. I have had three different guys out to check freon and everything else. What has me confused is that all three of them think this unit should be big enough. The filter is 20x20 and the return air is 24x24. Condenser is 2.5t Goodman and he said the coil is 2.5-3t. Any ideas would be appreciated. If I let it run for 24hrs the thermastat goes down to 82 in the morning and stays at 85 all day long. During the day I am seeing 65 out of the register.

This seems like a nightmare. A friend that does A/C told me that I needed a 2.5t unit for a house I just finished renovating. Its a New Orleans single shotgun style off the ground with T&Grove floors. 1000sq' with 10' ceilings. I insulated the walls and attic very well. I still plan to spray foam under floors but I dont think that will make a big difference to fix this problem. When we went to get the unit the guy at the supply double checked and agreed that 2.5 was the way to go. Unit was installed a couple weeks ago and the house has not seen temp under 82 degrees. The split between return is around 17. Copper sweats outside. The unit never shuts off. I have had three different guys out to check freon and everything else. What has me confused is that all three of them think this unit should be big enough. The filter is 20x20 and the return air is 24x24. Condenser is 2.5t Goodman and he said the coil is 2.5-3t. Any ideas would be appreciated. If I let it run for 24hrs the thermastat goes down to 82 in the morning and stays at 85 all day long. During the day I am seeing 65 out of the register.

What is the average summer temp. and humidity for your location (NOLA) I presume? Did anyone actually do a manual "J" heat loss/gain calculation?
If you've had three contractors say the system is sized correctly come out, what do they think the problem is?
More information would be helpful.

Heat Loss/Gain was done. The three techs all seem confused as to why the unit is not working. They say since the split is around 17 the system is doing its job. Basically they say that the 2.5t unit should be big enough but apparently since the split is what it is and its not working then I need a bigger unit. What confuses me is all three of them go away scratching their heads wondering why it is not working. The only reason that three guys came out is because I happen to know several A/C guys. I asked all three of them if adding 1/2 Ton should do it. They all said it should but said to be safe go with a 3.5. My coil is 2.5-3ton. Im guessing I can just change the condensor to a 3 ton but since I can not get under 85 during the night is that going to do it? Another problem is that the attic unit will not fit down the staircase where the contractor put the stairs. So if I upsize to 3.5 I have to cut out a ceiling. Since the coil is a 3 ton if I change the condensor to a 3 ton do I have to change the heater and blower out anyway? TIA!

Average Temp for August is 81. Relative humidity is morning=90 and afternoon=65

Average Temp for August is 81. Relative humidity is morning=90 and afternoon=65

Now I'm a little confused too. It must be hotter than 81 outside if the best you can get is 82 inside. A summer design temp of 81 degrees is not hot but the humidity seems pretty high. Nevertheless, with a indoor coil drop of around 17 degrees and you're not able to get the indoor temp but to 82, it must be considerably hotter than 81 degrees outside.
With the data you have, it makes me think the outdoor temp would be near 100 with 90%RH if your manual J was figured using accurate information.

I got those averages from a web site. This week when I was taking the measurments the temp's were 90high and 77lows. When it was 90 outside I could not get lower than 85 and when 77 at night I couldnt get lower than 81-82. Split seems to bounce around 17-20.

Just wondering...more for my own info...could the blower speed affect the cooling? Would increasing it help or hurt?

I've read some things about optimal air movement, but I'm still not clear on it... Just a thought.

Right, If its 77 outside and 82 inside why cant that split at least make the air inside as cool as outside. It almost seems there is a heat source inside which there is not. I do not have any vents in the attic but it does not seem to affect the split.

I got those averages from a web site. This week when I was taking the measurments the temp's were 90high and 77lows. When it was 90 outside I could not get lower than 85 and when 77 at night I couldnt get lower than 81-82. Split seems to bounce around 17-20.

Are you saying it was around 77 outside at night and the indoor temp was 82 in the morning and you have a split of 17 degrees?
Is there much condensation coming from the drain?

Im not sure about the condensation because the line runs down a wall into a p-trap in the wall. I do not think I can tell how much there is. On a side note I tried blocking off three ducts out of six. Basically eliminating 1/2 of the house. After two hours at night the temp went from 82 to 80. Not a scientific test but I am grasping for straws at this point.

Im not sure about the condensation because the line runs down a wall into a p-trap in the wall. I do not think I can tell how much there is. On a side note I tried blocking off three ducts out of six. Basically eliminating 1/2 of the house. After two hours at night the temp went from 82 to 80. Not a scientific test but I am grasping for straws at this point.

Are there only 6 registers or supply ducts and what size are they?

Yes there are only 6 registers. I will have to measure them today. On another note I thought I had the problem fixed when I found out the original installer did not put the 2.5 t piston in the coil. We changed it to 2.5 from the 3t but no difference. Here is the problem we are having.
Low side pressure=100
High side =300
Super heat =25
Super heat will not go down
50' of tubing
He said he likes to see the super heat at 10.

Just wondering...more for my own info...could the blower speed affect the cooling? Would increasing it help or hurt?

I've read some things about optimal air movement, but I'm still not clear on it... Just a thought.

Nobody has answered this yet and this is a very good question that has a logic behind it. But if you think about it, on a simple mechanical level only - a given ton(s) unit can only produce so much cool. By increasing the fan speed per given size ton unit, you can blow more air, but at the expense of the temp coming out maybe increased a degree or 3.

Or if you slow the fan speed, the air would get colder, but you'd move less of it. Sort of a wash, I would think.

But I'm sure people in the business, especially on the engineering end, may have a more precise answer, that may deal with frictional loss, humidity and ?. But a/c fan speed is run at a faster speed than for heat.

And that stands to reason based on a simple windchill effect. So with cooling you want to take advantage of that effect. But for heating you don't, because say if you had your house set to 68 in the winter, you woud not want to feel drafty 68 degree temps, as that would feel cold.

First 17 accross the coil is very good. 65 at the reg is also good.

100 Suction would be because it's sucking in hot air and 25 superheat is also direct evidence of that. 300 discharge is a direct result of suction. Would like to know subcooling though.

I think you are looking at an air problem. 20x20 filter in one 24x24 return, or is the actual return duct 24x24? Or is it actually a 24x24 grill with flex to unit?

1000 sqft with 6 supplys. Does that mean 3 or 4 rooms? Are the doors kept closed? If so what is the cut at the bottom of the doors?

Any restrictions in duct work? Dampers not fully open?

I open my load calc program and made a sigle room 1000sgft with 10 foot ceilings. Added a couple other parameters but no doors or windows. Tells me I need 1359 CFM for the room.

In order to properly heat and cool my room I need to supply 1359 CFm. But if I am not also returning 1359 to the a/c I'm not cooling squat.

Think of it this way. You can dump 300 cfm of cold air into a room all day long. If your not also removing 300 cfm of hot air, your not going to cool anything.

Back to super heat, don't like anything. In the lterature supplied and should be on the back of condenser panel are charging charts. That's what tells you where superheat should be under various conditions.

Hope this helps.

Questions answered in line. BTW, Tonight I removed the filter from the unit just to see what would happen. The split dissapeared. I had 82 at the register and the exact same thing at the return. Put the filter back and the 17 degree split showed up again. Should I have seem some split without the filter in the unit?

First 17 accross the coil is very good. 65 at the reg is also good.

""Thats what I thought. ""

100 Suction would be because it's sucking in hot air and 25 superheat is also direct evidence of that. 300 discharge is a direct result of suction. Would like to know subcooling though.

I think you are looking at an air problem. 20x20 filter in one 24x24 return, or is the actual return duct 24x24? Or is it actually a 24x24 grill with flex to unit?

""The return from floor to ceiling is 24x24. The filter that fits in the grill is 20x20. ""

1000 sqft with 6 supplys. Does that mean 3 or 4 rooms? Are the doors kept closed? If so what is the cut at the bottom of the doors?


""About an inch clearence at bottom of doors. I have two ducts in the front room which is a double room opened up. I have another duct in each of two bedrooms. Then one small duct in each of two baths. Not sure of the size of the ducts. Maybe 9" and 4" for the bathrooms??""



Any restrictions in duct work? Dampers not fully open?

""I forgot to check the dampers. Someone suggested I check that. I will in the morning though. ""



I open my load calc program and made a sigle room 1000sgft with 10 foot ceilings. Added a couple other parameters but no doors or windows. Tells me I need 1359 CFM for the room.

In order to properly heat and cool my room I need to supply 1359 CFm. But if I am not also returning 1359 to the a/c I'm not cooling squat.

Think of it this way. You can dump 300 cfm of cold air into a room all day long. If your not also removing 300 cfm of hot air, your not going to cool anything.

Back to super heat, don't like anything. In the lterature supplied and should be on the back of condenser panel are charging charts. That's what tells you where superheat should be under various conditions.

Hope this helps.

""Sunday Morning I have a guy comming out and he is supposed to be a HVAC Guru. Ill post what we find tomorrow. Thanks to everyone for the advice.""

You are picking up heat from somewhere and it is not being reflected in your temperature readings if you are taking an intake temperature reading at the filter and your return duct is leaking in the attic or your electric hat is stuck on your temperature readings won't reflect it I am sorry that 3 guys are scratching their heads but something is not as it seems. I'm guessing return duct leak in attic, check it out.

Questions answered in line. BTW, Tonight I removed the filter from the unit just to see what would happen. The split dissapeared.
""The return from floor to ceiling is 24x24. The filter that fits in the grill is 20x20. ""

Filter at unit and in grill? You don't have 2 filters do you? Or was that just wording?

:thinker:

I'm not an A/C tech but I have an idea. Since pulling this big unit out and replacing it might be unacceptable to you at this time, could you try using portable dehumidifiers in various rooms?

I don't live in a high humidity area like NOLA, but it's been pretty humid here in SoCal this summer. I bought a portable A/C that happens to have a dehumidifier built in. Sometimes I used the dehumidifier alone and it really cools down the room a lot.

Like I said, I'm just suggesting this to offer an idea that might help this big unit do it's job better and prevent you having to pull it out and replace it.

Well, I met this guy today. He is an old timer looking for a challenge type of guy. He took his time and checked the whole unit out. Looked for leaks, adjusted the freon.


One thing that concerns me that might not matter but he removed the cover from the top of the coil. There was a 1" clearence where are can go over the coil instead of through it. Thats the way the coil came in the case. He blocked that clearence off with styrofoam. Is that ok?


Other than that he said the guy that did the caculations for the unit and came up with 2.5t did not consider the old windows and a few paper size cracks in the floor. Also no vent ridge cap. The house is on the historic register and I just cant bring myself to put new modern windows in it. I am getting someone to foam under the floors next week which he said will help. Also I have a clay ridgecap that prevents me from putting a ridge vent in. I have heard some bad things about powered attic vents.



He also said to remove the 2.5t coil piston and put a whatever valve which would bring it to a true 13 seer. He said if I do all of this then it will be borderline so I am going to bite the bullet and change the condensor to a 3t since everything in the attic can stay the same. Ill pay 1k or so for the 3t and sell the 2.5t condensor for 600.00 or so. Ill be out 400.00 but no big deal. Im just glad to know that everything else is ok. Im sure glad we got a 3t setup in the attic.

I'm sorry but I still did not hear whether the possibility of warm air infiltrating the return was addressed

If what you are asking is about leaks in the return duct the answer is yes. I ran another layer of tape and that gray paint stuff over every seam in the return and in the attic. Return air duct is sealed.

And you still have a 17 degree drop and your indoor temp is not dropping, I would be buying some blinds and a caulking gun

The house is pretty tight other than the old windows which I have covered in paper yesterday. The floor should be insulated this week. Regardless though what would make the pressures so high and the super heat refuse to come down lower than 25. Thats what has everyone confused. Being undersized wouldnt have a factor right? I should be able to put a one ton unit in here and still see correct pressures right? I can put my face over the condensor unit and see its just not getting the heat out. I called goodman just now and they agree the pressures are wacked as well.

Those high pressures sound like warm air infiltrating the return again I know you said you checked it but if it is not leaking is it insulated

. BTW, Tonight I removed the filter from the unit just to see what would happen. The split dissapeared. I had 82 at the register and the exact same thing at the return. Put the filter back and the 17 degree split showed up again. Should I have seem some split without the filter in the unit?



Just spotted this. This could be a big clue.

I can't get into this as my time is alotted here and I have to check out other posts from yesterday.

As of now I am supposed to have a warranty guy comming out that can handle the warranty work from Goodman. I think there is a bad part somewhere. I decided to go this route instead of going with a 3T replacment. Something is causing these wacked pressures and they need to be fixed first. Ill see what happens tomorrow.

Be sure to tell him about your filter experiment. That is really odd. Indicates some blockage I think. I have not had time to give this much thought. My car has been weighing heavily on my mind lately.

Well, after talking to goodman techs and having other techs look over the unit I am convinced I have a bad condensing unit. I am going to swap it out tomorrow. Everyone agreed that if the superheat gets stuck at 25 the unit can not do its job. Its a brand new line set and they say if the piston is put in right then they pretty much rule out a problem with the new coil. So, I feel confident tomorrow Ill be hanging meat in this house.

1000sq' with 2.5t should be good enough if the house is insulated right. Here the only question I have is : You said 17 degree split, do you mean your return temp minus your A/C output temp is 17 degrees ? another word, if your room temp is 82, then, the air come out of your A/C should be 65 degree. Is this correct ??

I think you have a bad something.

As said, the 2.5 should be ok.

I hope you don't install the 3 ton and have the same problem.

While the system is empty, check to ensure the correct 2.5 piston is in and in the corect way.

I am getting very close. :) I swapped out the unit with the 3t and the first test I did was removed the airfilter to see if it was still cooling. It does and I still have the split. The new unit cools very well and cycles like it should. The old condensor was defenintly bad. I pulled out the piston and installed an expansion valve. The guy at the A/C place suggested this and also said I should install a kickstart when going with the expansion valve. I did not install the kickstart yet and noticed that every time the condensor turns on the compressor tries to start but does not. It takes a few minutes and two or three tries for it to start running. Then all is well. Is this probably from the expansion valve? Can someone give me an idea how to install the kickstart? Its a T-O5. I see its only got two wires. Does it go in the condensor? Also, two days after I installed the unit I got the underfloor foamed with open cell. I already noticed the unit cycling more often. TIA

I am getting very close. :) I swapped out the unit with the 3t and the first test I did was removed the airfilter to see if it was still cooling. It does and I still have the split. The new unit cools very well and cycles like it should. The old condensor was defenintly bad. I pulled out the piston and installed an expansion valve. The guy at the A/C place suggested this and also said I should install a kickstart when going with the expansion valve. I did not install the kickstart yet and noticed that every time the condensor turns on the compressor tries to start but does not. It takes a few minutes and two or three tries for it to start running. Then all is well. Is this probably from the expansion valve? Can someone give me an idea how to install the kickstart? Its a T-O5. I see its only got two wires. Does it go in the condensor? Also, two days after I installed the unit I got the underfloor foamed with open cell. I already noticed the unit cycling more often. TIA

I think you are getting close to figuring out what damaged your original compressor if that thing is brand new and it is having trouble starting you got a problem it sounds like your pressures are not equalizing after shutdown that means when the compressor tries to start it is pushing against 175 to 250 pounds of pressure you can combat this by putting a hard start kit on it but if you don't find out why you aren't equalizing this compressor is not going to last long

Just wanted to post a followup. Everything is working great! Thanks for all the ideas. After noticing the compressor not kicking on immediatly after installing the expansion valve I called the A/C distributor. The sales rep said this is why he sold me the hard start kit. He said some compressors need this when going with expansion valve. I installed it a few days ago and everything works great. I hope he is right. Also after putting in the new condensor all the pressures were in line so Im sure the other condensor was bad. One more note. I am amazed at the difference I am seeing after getting the Co to foam underfloor with open cell foam. The foam actually came in the house through some of the small cracks and even small nail holes that were in the floorboards.

100 Suction would be because it's sucking in hot air and 25 superheat is also direct evidence of that. 300 discharge is a direct result of suction. Would like to know subcooling though.

While I think this could be a correct statement, in this case it appears it was due to bad valves in the comp or a bad reversing valve.

Never correct 100% of the time.

Mike, After reading your post I called Goodman tech line. He confirmed that a hardstart kit is needed when going with an expansion valve. He also said it is in the manual for this reason. It seems odd to me as well that it would be absolutly nesessary as you mentioned.

First I have heard of a manufacturer requiring a hard start kit on a new peice of equipment but it does't surprise me considering the source

Units are made daily with hard start kits. Either start relay and start cap, or PTCR.

It is not at all uncommon for the manufacturer to require a hard start when a txv is installed vice piston/orifice.