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  1. #1
    Join Date
    Nov 2010
    Location
    Central Florida
    Posts
    556

    New Roof, AC Seems to be struggling a bit?

    Hi,

    Just had a new roof put on my home and noticed the AC seems to be struggling a bit during peak afternoon hours with about a 77 degree indoor setting. 3 ton Carrier Split heat pump system only 2 years old. Single story home, AHU inside a closet indoors.

    I'm trying to determine if maybe the new roof (going from 3-tab to architectural shingles) and a 15# felt to 30# felt might be the issue trapping more heat. Same color shingles as before (medium gray). Another change is the ridge vent - used to be a standard aluminum 18 sq in/ft net free air and now is a high-performance plastic low-profile Lomansco with just 11 sq in/ft net free air. When there is wind it pulls well, but in stagnant air it obviously does not have the same net free air space to vent.

    The other thing I noticed is the liquid line entering the AHU becomes warm when running at temps over 85 degrees outside. Below 80 degrees the line is very cool to the touch. Is this normal or reflective of a charge issue, TXV issue or dirty outdoor condenser coil fins? (Visually they don't really appear dirty or clogged)

    At peak afternoon heat around 90 degrees outside the attic temps are now running about 30+ degrees greater than outside temps. (120-125 range)

    SO.....question I'm trying to narrow down is this: Is the AC functioning okay or is the attic just excessively hot due to something related to the new roof, which is then possibly effecting the AC performance? This isn't a DIY but just trying to get a direction on this before calling anybody to look at the situation. I figured the HVAC experts may have ran into this kind of thing before.

    Many Thanks,

    Sonic

  2. #2
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    6,735
    Possibly a little of both, if the liquid line is warm/hot the condenser is probably dirty or condenser fan could be struggling/stopping.

  3. #3
    Join Date
    Nov 2010
    Location
    Central Florida
    Posts
    556
    Quote Originally Posted by jtrammel View Post
    Possibly a little of both, if the liquid line is warm/hot the condenser is probably dirty or condenser fan could be struggling/stopping.
    Fan is fine. On my previous 20 year old Carrier recip I never had to have the condensor cleaned but with these new high SEER Scroll units I'm not sure what is required. Sure looks like a lot more coil fins packed closer together, but then again I can't honestly say I ever paid attention to the old recip enough to be able to say if there was a difference. Is there a particular temperature I should be getting on the liquid line that will indicate if I should call somebody out to check & clean the condenser coils? And would I measure at the AHU or the condenser? Is cleaning part of a basic service call or do I need to specifically request it?

    Thanks for the help.

  4. #4
    Join Date
    Jul 2007
    Location
    Mount Airy, MD
    Posts
    7,281
    Thread relocated to AOP

  5. #5
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    If the air is the same temp out of the registers as before, than hte roof could be contributing, expecially if its' an attic installation. The change in ventilation would be the biggerst change. How many layers of shingles were removed? Additional shingle layers may have acted as a insulator and vapor barrier. A hot roof will drive humidity into an attiuc. IF hte equipemtn or ducts are in the attic, the increase latent load, combiend with less ventilation can make a big difference.

    Now if hte air is significantly warmer, then your problem might be the condenser. ALL air cooled coils will need regular cleaning. I don't think the older equipment was any more or less sensitive to air movement across the coil. Higher refrigerant pressures from less heat transfer will result in less effciency and capacity.

    It's also possible that yoru system developed a leak and it's jsut a coincidence that your seeing it now.

    Liquid line temperatures are useless without knowing the pressures.

  6. #6
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,963
    Quote Originally Posted by SonicExplorer View Post
    Hi,

    Just had a new roof put on my home and noticed the AC seems to be struggling a bit during peak afternoon hours with about a 77 degree indoor setting. 3 ton Carrier Split heat pump system only 2 years old. Single story home, AHU inside a closet indoors.

    I'm trying to determine if maybe the new roof (going from 3-tab to architectural shingles) and a 15# felt to 30# felt might be the issue trapping more heat. Same color shingles as before (medium gray). Another change is the ridge vent - used to be a standard aluminum 18 sq in/ft net free air and now is a high-performance plastic low-profile Lomansco with just 11 sq in/ft net free air. When there is wind it pulls well, but in stagnant air it obviously does not have the same net free air space to vent.

    The other thing I noticed is the liquid line entering the AHU becomes warm when running at temps over 85 degrees outside. Below 80 degrees the line is very cool to the touch. Is this normal or reflective of a charge issue, TXV issue or dirty outdoor condenser coil fins? (Visually they don't really appear dirty or clogged)

    At peak afternoon heat around 90 degrees outside the attic temps are now running about 30+ degrees greater than outside temps. (120-125 range)

    SO.....question I'm trying to narrow down is this: Is the AC functioning okay or is the attic just excessively hot due to something related to the new roof, which is then possibly effecting the AC performance? This isn't a DIY but just trying to get a direction on this before calling anybody to look at the situation. I figured the HVAC experts may have ran into this kind of thing before. Many Thanks, Sonic
    It is possible there could be a Return air leak allowing hot humid attic air getting sucked into the return.
    Record the discharge air temperature coming off the outdoor condenser & then subtract the outdoor temp from it.

    For the test to be meaningful, make sure the condenser is clean & dry before running the temp checks below.

    At 90F outdoors & 75F & 50% relative humidity indoors the condenser air-temp-split should not be above 17F; @ 80F & 50% indoors the split should not be above 22F. If at 50% indoor RH & those temps, the temp-splits are above the listed split levels, it could be drawing hot air into the Return from a hot unconditioned space, like the attic. Hardware stores usually have low cost humidity gauges, every home needs one.

    Especially, if it has a Return chamber under the furnace, every possible entry point must be totally sealed from any source of unconditioned air.

  7. #7
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,875
    I'd say its a combination of a dirty condenser coil. And not enough ridge vent.
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  8. #8
    Join Date
    Feb 2009
    Location
    Tallahassee, FL
    Posts
    6,031
    I'm calling a nail in the suction line!

  9. #9
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Quote Originally Posted by SBKold View Post
    I'm calling a nail in the suction line!

    I had that happen when i lived in a condo. Lineset was run up near the rafters.

  10. #10
    Join Date
    Feb 2009
    Location
    Tallahassee, FL
    Posts
    6,031
    Quote Originally Posted by motoguy128 View Post
    I had that happen when i lived in a condo. Lineset was run up near the rafters.
    Happened to 2 of our jobs. Roofers claimed no responsibility on either. One one they hit the suction line in 3 spots.

  11. #11
    Join Date
    Feb 2012
    Location
    Michigan
    Posts
    87
    This is the Ask Our Pro's forum, and only Pro members that have been vetted by the AOPC may post advise, commentary, or ask questions of the OP here.

    You can find the rules for posting and qualifications here.

    Further infractions may result in loss of posting privileges.
    Last edited by beenthere; 05-25-2013 at 06:43 PM. Reason: Non Pro * Member

  12. #12
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,875
    Homeonwer314, this is the Ask Our Pro's forum, and only Pro members that have been vetted by the AOPC may post advise, commentary or ask questions of the OP here.

    You can find the rules for posting and qualifications here.

    Your post has been deleted.
    Further infractions may result in loss of posting privileges.
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    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  13. #13
    Join Date
    Nov 2010
    Location
    Central Florida
    Posts
    556
    Many thanks to all who replied.

    To clarify: One shingle layer, attic ducts, lineset under ground (under the slab).

    I suspect a combination of slightly dirty condensor mixed with ventilation that is just not keeping up. Now, could be NEW heat generated by the new roof or it could be the SAME heat just not ventilating as well with the new ridge vent.

    Not sure this provides a clue or not, but once the attic and outside cools to 80 degrees or less the A/C blows very cold as usual. It is when the attic starts exceeding about 110 degrees and the outside exceeds about 85 that the air from the ducts is not quite as cold, and so the system starts running a lot to keep up. It is still very cool, but not quite as cold. Perhapes I should do a Delta T test from intake to exhaust on the AHU?

    The other possibility, as somebody pointed out, is maybe a slow leak. I did notice something today that I do not recall seeing before... On the liquid line where it connects to the drier outside of the condenser I am seeing what looks like little "blisters" in the copper at the braze joint. Would this by chance be a symptom if Puron had been slowly leaking? I will try to take a picture and see if I can figure out how to upload it....

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