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  1. #1
    Hi all,

    I am new to this forum. I recently have a new A/C system installed. However, it performs only marginally better than my 25-year old system, which is replaced by the new one.

    It suffers the same problems with my old system:
    1. Cool very slowly. The indoor temperature only drop 4F after running 3~4 hours
    2. Runs 19~20 hours a day, when the ourdoor tempearture is 90~72F range and indoor temp is set to 75F, and it can not maintain the target temperature after 10:30AM the next day (the minimum it can maintain is 76F) and run continuously from 2:30PM till midnight, and from 10:00AM till 5:00PM the next day (I stop the system after that)

    I observed pretty much the whol installation process and after I received manuals and read it later on, I found the following steps specified in installer's guide are skipped, which may be the root cause of the problem:
    1. No Leak Check
    2. No System Evacuation
    3. No operational testing (air temperature, refrigerant pressure, outdoor air temp, etc) and I am not sure the freon is properly charged

    I know skipping those steps are no good, can anyone point me to some resources that can prove how bad it can be?

    Additionally, what is your typical experience of your A/C system? And what is your expectation of a new system? Specifically:
    1. how long do you expect your room temp to drop to a comfortable level after you turn on A/C on an average summer day?
    2. how long do you expect your room temp to reach your target temp and your A/C goes to an on/off cycle?
    3. how many degree F do you expect your A/C system to be able to drop compare to an outdoor temperature of 91 degree F?
    4. How many hours do you expect your A/C system to run on an average summer day (say outdoor temp between 72~91F, target temp set to 75F) if it's properly sized?
    5. On the hottest day, how many degree F can your A/C drop compare to outdoor temperature?

    Thanks in advance for any information and any advise on how to fix the problem.

    [Edited by grandtiger on 07-10-2006 at 10:31 AM]

  2. #2
    deleted

    [Edited by grandtiger on 07-10-2006 at 10:24 AM]

  3. #3
    grandtiger,

    Did you check on how did the person perform load calculation, and calculation for ductwork?

    1. About 3-5 minutes.
    2. Depends on the set temperature. Lower set temperature will require it to run longer.
    3. about 20-25 degrees F.
    4. You mean the compressor? See (2).
    5. Mine is sized properly. It can keep my room at 16 degrees C, even during hottest days (35 degrees C).

  4. #4
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    I am a homeowner not a pro. Why don't you try just calling the installing company and tell them you are not satisfied? You expected the new system to pull down temperatures better than the old one, and to run less. That does not guarantee you good results, but it follows good business manners to give the original guy(s) a chance to set things right.

    You should NOT have to defend yourself, and I think it a mistake to try to dissect what they should have done and argue those details with them. Save that for later if really necessary. I think it's a mistake to try to look for proof that what they left out, has bad consequences. Your AC cooling your house (with good humidity control) and running for years without breaking is the main proof. If they were hacks, you may not get very far with them, but you gotta try.

    Most of your questions about performance are very dependent on sizing. A system sized properly according to ACCA Manual J, as I understand is expected to run several hours nonstop during the hotter days, and perhaps to not maintain the thermostat setpoint for brief periods in the hottest days. Very few systems are actually undersized, if yours fails to perform then there is probably another problem to fix.

    During the Manual J sizing model, you are asked to input design conditions for indoors and outdoors. So there is no one answer to your question about holding X degrees below outdoor. My own design conditions assume 94 to 99 outside and 75 inside. The 94 outdoor temp is recommended by the software, I did a cheat up to 99 because of remembering 1980 which had many 100+ days. My system has been observed to run 2-3 hours nonstop and I believe I want to not exceed that number -- just my opinion not a pro's judgement.

    It would be very useful to ask the techs to check your "External Static Pressure" (ESP) and your airflows if they have that capability. That may reveal an airflow problem which is keeping your system from putting out as many cooling BTUs as it should. If your old tech fails to satisfy, I would consider one trained by the National Comfort Institute:
    http://www.nationalcomfortinstitute.com/

    You say you are not sure the freon is properly charged. Is it your job to be sure of that, or the tech's? I think that you should be working with a company you can trust, rather than trying to second guess them. Those other steps you say were not done, you have a legitimate thing to discuss with your AC company, just do it. Perhaps ask for the manager rather than the installing tech.

    I think it best to work as much as you can with the original AC company, there must have been some good reason you chose them. Sometimes you can get the AC manufacturer to work with you and that company to try to get a quality install. Even if you have to go to a 2nd AC company to set things right, you gotta do what you gotta do.

    Best of luck -- Pstu

    P.S. On this board you can edit your post if you want, rather than adding a second one right after.

  5. #5
    Hi mjk_na,

    Thanks for your reply.

    As for the size/capacity, I believe it's enough and properly slightly oversized. I have a two-bedroom condo at the third (top) floor with 1100 sq.ft. and the system is a two-ton (24,000BTU) system. I got free esitimates from about 5 contractors, and they all quotes the same size.

    The system was first started around 2:30PM when outdoor temp was 91F (the highest temp of the day, after that it slowly decline to 90, 88 and 87 by 5:30PM), and the target temp is set to 75F and indoor temp was 85F. Do you think this is normal for a new system?

  6. #6
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,472
    A/C units are good at maintaining but try to get them to drop a hot place on a hot day and good luck. My unit will let me hang meat even in 90+ steamy weather but only if it starts out cool. A week ago on a hot day, I opened the house first thing in the morning to air it out. But was gone until mid afternoon and the house got up to 81. It took 12 hours to get the house back to 70 and that was because it really cooled down outside after sunset. If I had left the unit on and windows closed, it would have had no trouble holding 70.

    If you are in the 90s, you may not get it to drop much but should maintain mid 70s running constantly as long as you don't let it warm up then turn it down.

  7. #7
    Hi pstu,
    Thanks a lot for your advice.
    However, the reason that I asked for help here is because I can not get help from the company that installed the system.
    They tried to avoid me, they denied any wrong-doing, I left them messages described the problem of the system, but they did not listen to them carefully and never call me back and discuss the problem, and even when I spoke to the owner, he never let me speak instead blame me being nasty and mean and hung up on me. They keep making untruthful claims that they gave me first-class system, they did first-class job, and the reality is that they did not even follow the manufacturer installer's guide.
    I guess I didn't do enough research and I am too naive as an immigrant expecting much better things in the America. They also appears to discriminate against me.
    I know they did not install the system properly, but I don't know how to fight and win this war.
    Anyone has similar experience or know what's the right thing to do, please help!!!

    Originally posted by pstu
    I am a homeowner not a pro. Why don't you try just calling the installing company and tell them you are not satisfied? You expected the new system to pull down temperatures better than the old one, and to run less. That does not guarantee you good results, but it follows good business manners to give the original guy(s) a chance to set things right.

    You should NOT have to defend yourself, and I think it a mistake to try to dissect what they should have done and argue those details with them. Save that for later if really necessary. I think it's a mistake to try to look for proof that what they left out, has bad consequences. Your AC cooling your house (with good humidity control) and running for years without breaking is the main proof. If they were hacks, you may not get very far with them, but you gotta try.

    Most of your questions about performance are very dependent on sizing. A system sized properly according to ACCA Manual J, as I understand is expected to run several hours nonstop during the hotter days, and perhaps to not maintain the thermostat setpoint for brief periods in the hottest days. Very few systems are actually undersized, if yours fails to perform then there is probably another problem to fix.

    During the Manual J sizing model, you are asked to input design conditions for indoors and outdoors. So there is no one answer to your question about holding X degrees below outdoor. My own design conditions assume 94 to 99 outside and 75 inside. The 94 outdoor temp is recommended by the software, I did a cheat up to 99 because of remembering 1980 which had many 100+ days. My system has been observed to run 2-3 hours nonstop and I believe I want to not exceed that number -- just my opinion not a pro's judgement.

    It would be very useful to ask the techs to check your "External Static Pressure" (ESP) and your airflows if they have that capability. That may reveal an airflow problem which is keeping your system from putting out as many cooling BTUs as it should. If your old tech fails to satisfy, I would consider one trained by the National Comfort Institute:
    http://www.nationalcomfortinstitute.com/

    You say you are not sure the freon is properly charged. Is it your job to be sure of that, or the tech's? I think that you should be working with a company you can trust, rather than trying to second guess them. Those other steps you say were not done, you have a legitimate thing to discuss with your AC company, just do it. Perhaps ask for the manager rather than the installing tech.

    I think it best to work as much as you can with the original AC company, there must have been some good reason you chose them. Sometimes you can get the AC manufacturer to work with you and that company to try to get a quality install. Even if you have to go to a 2nd AC company to set things right, you gotta do what you gotta do.

    Best of luck -- Pstu

    P.S. On this board you can edit your post if you want, rather than adding a second one right after.

  8. #8
    Join Date
    Dec 2002
    Location
    Rochester, MN
    Posts
    5,305
    The system was first started around 2:30PM when outdoor temp was 91F (the highest temp of the day, after that it slowly decline to 90, 88 and 87 by 5:30PM), and the target temp is set to 75F and indoor temp was 85F. Do you think this is normal for a new system?
    That's your problem!


    If you know for a fact fit the day time temp is going to be hot, start the unit in the moring or the day before! Once it's on, set it and forget it.

    A/C does not pull the temp down fast like a heating system does.

  9. #9
    Join Date
    Jul 2006
    Posts
    1,091

    if they skipped

    System Evacuation
    operational testing (we just call it start up) you may have some problems, but a unit sized proper will KEEP UP not CATCH UP at load conditions

    If the equipment is sized for 93 degrees outdoor and 75 degree indoor and it IS 93 outside and you have controls set at 75 the equipment will not stop running until it is cooler outside or you set the controls higher inside.

  10. #10
    Join Date
    Jun 2006
    Posts
    628
    The installation is done, nothing is likely actually "wrong" with it, and almost certainly nothing is going to be done by the contractor to materially change its operation.

    Condos are notorious for problems, insulation not really as good as it should be, not sealed as well as it should be, and three levels are difficult to manage temperatures in anyway.

    Before the install you should have required the contractor to do a heat load calculation, but its very common that contractors skip that unless requested when replacing a system.

    Many consumers get efficiency and capacity mixed up. Your new unit is almost certainly the same capacity as the old one, and cools no better or worse than the old one. The increased efficiency doesn't make it cool any better, in some cases not as well, but to operate using less power.

    Set the thermostat to 75 and leave it on and see if it can hold that temperature.

  11. #11
    sounds like nothing is wrong and how do you know that they skipped these steps were you over their shoulder the whole time i sure hope for there sake you were not. operation sounds normala nd to get proper dehumidification long runs cycles are the norm. i would first relx turn the stat to 75 walk away and if she holds 75 on a hot day and turns off at least a little bit relax there is more then likely no issue. If i was the contractor and some home owner who knows nothing says we didnt do things when i know my guys did I would be kinda upset as well. If you know so much why didnt you do it yourself. And save the contractor the hassel also to cut down on run time you coulda put in a 5 ton system it wount run very long but your house may feel like the rain forest

  12. #12
    I got a few quotes and some did load calculation, so don't. Most of them agree that two-ton is slightly oversized, the old one is mostly likely only 1.5 ton because it's used on both 1-bedroom and 2-bebroom units when the condos were built.

    I do understand the difference between efficiency and capacity. And neither of them hold up to my expectation. I set target temp to 75F and kept the system running for 27.5 hours (2:30PM to 5:00PM the next day). It took 10 hours to get to the target running continuously, while the outdoor temp has dropped from 91F to 76F. But it can not hold that temperature the following day starting from 10:00AM, it started running continuously again. The on/off cycles only happened between mid-night and 10:00AM. I think it's very inefficient, only marginally improved compared to my 25-yr old system.

    Originally posted by danglerb
    The installation is done, nothing is likely actually "wrong" with it, and almost certainly nothing is going to be done by the contractor to materially change its operation.

    Condos are notorious for problems, insulation not really as good as it should be, not sealed as well as it should be, and three levels are difficult to manage temperatures in anyway.

    Before the install you should have required the contractor to do a heat load calculation, but its very common that contractors skip that unless requested when replacing a system.

    Many consumers get efficiency and capacity mixed up. Your new unit is almost certainly the same capacity as the old one, and cools no better or worse than the old one. The increased efficiency doesn't make it cool any better, in some cases not as well, but to operate using less power.

    Set the thermostat to 75 and leave it on and see if it can hold that temperature.

  13. #13
    youll probloy be surprised when you get your gas bill the system sounds like it runs like mine and is very effeicnt i set it for 70 all the time and have very low bills

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