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  1. #1

    New System Needs Tweaking ?

    Hello,

    I've been a long time lurker on this great forum and now I could really use some advise.
    To begin I have 1800 sq ft with 11 registers (2 in 2 rooms,1 in all others) and a 20X30 return.
    I recently replaced my 17 yr old Carrier (38CKB) 3T, which was working fine but the evap was rusting out.
    It was replaced with a Carrier 24ABC 3T, 58PHA090 furn, and CSPHP4812 coil.
    Now both units were 42K btu, and 88K for the furnace,but the old system had the "N" type coil.
    All the "pros" recommended the Slab type for the SE Texas hot and humid climate.
    The first thing I've noticed is the new system doesn't seem to have the same "pull" toward the return ?
    Also, the output doesn't seem as strong and the rooms get stagnate quickly once the unit shuts off.
    The output is cool, but with the old system it would remain comfortable until the next cycle.
    Both run about 8 min cycles, and I noticed the old plenum had only 4 outlets compared to 6 on the new install ?
    So if all the "specs" match up, and the only variant is the Slab coil versus the "N" coil,could that be the culprit after all ? Perhaps the humidity is now noticeably out of balance ?
    The installer is coming back out tomorrow to address my concerns, but any input would be greatly appreciated.

  2. #2
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,062
    Quote Originally Posted by aworkinprogress View Post
    Hello,

    I've been a long time lurker on this great forum and now I could really use some advise.
    To begin I have 1800 sq ft with 11 registers (2 in 2 rooms,1 in all others) and a 20X30 return.
    I recently replaced my 17 yr old Carrier (38CKB) 3T, which was working fine but the evap was rusting out.
    It was replaced with a Carrier 24ABC 3T, 58PHA090 furn, and CSPHP4812 coil.
    Now both units were 42K btu, and 88K for the furnace,but the old system had the "N" type coil.
    All the "pros" recommended the Slab type for the SE Texas hot and humid climate.
    The first thing I've noticed is the new system doesn't seem to have the same "pull" toward the return ?
    Also, the output doesn't seem as strong and the rooms get stagnate quickly once the unit shuts off.
    The output is cool, but with the old system it would remain comfortable until the next cycle.
    Both run about 8 min cycles, and I noticed the old plenum had only 4 outlets compared to 6 on the new install ?
    So if all the "specs" match up, and the only variant is the Slab coil versus the "N" coil,could that be the culprit after all ? Perhaps the humidity is now noticeably out of balance ?
    The installer is coming back out tomorrow to address my concerns, but any input would be greatly appreciated.
    The 8 minute cycle is quite short, probably leaving high humidity when the system shuts off.

  3. #3
    Quote Originally Posted by second opinion View Post
    The 8 minute cycle is quite short, probably leaving high humidity when the system shuts off.
    To the best of my recollection the old system ran about the same time, but I could be off by a bit? What should the average run cycle be to maintain say 76 deg once you've reached it?.
    (I know there are variables, but I'm well insulated,double pain windows,no open doors,etc.)
    So that explains the almost immediate stagnate feeling once it shuts off, but I'm also trying to figure out why lack of pull and circulation while it's running?
    I thought it could have been filter related so I changed from a 3M pleated 11MERV to a Honeywell 7 and no noticeable change in suction or flow?

  4. #4
    Join Date
    May 2008
    Location
    Missouri
    Posts
    3,615
    What type of furnace did you replace? Pilot light standard, 80% electronic ignition, or +90%? What was the input of the old furnace? What is the efficiency of the new furnace? Can you post some pictures of plenum set up?

  5. #5
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,744
    Quote Originally Posted by aworkinprogress View Post
    Hello,

    I've been a long time lurker on this great forum and now I could really use some advise.
    To begin I have 1800 sq ft with 11 registers (2 in 2 rooms,1 in all others) and a 20X30 return.
    I recently replaced my 17 yr old Carrier (38CKB) 3T, which was working fine but the evap was rusting out.
    It was replaced with a Carrier 24ABC 3T, 58PHA090 furn, and CSPHP4812 coil.
    Now both units were 42K btu, and 88K for the furnace,but the old system had the "N" type coil.
    All the "pros" recommended the Slab type for the SE Texas hot and humid climate.
    The first thing I've noticed is the new system doesn't seem to have the same "pull" toward the return ?
    Also, the output doesn't seem as strong and the rooms get stagnate quickly once the unit shuts off.
    The output is cool, but with the old system it would remain comfortable until the next cycle.
    Both run about 8 min cycles, and I noticed the old plenum had only 4 outlets compared to 6 on the new install ?
    So if all the "specs" match up, and the only variant is the Slab coil versus the "N" coil,could that be the culprit after all ? Perhaps the humidity is now noticeably out of balance ?
    The installer is coming back out tomorrow to address my concerns, but any input would be greatly appreciated.
    Is your furnace in the attic? The new slab coil is a 48,000 Btu, if I'm reading the numbers correctly. The new condenser remains a 3 ton? Slab coils are supposed to be mounted a minimum of 18" away from the furnace. You might check that. Also, when we mismatch a coil to a condenser (for the higher SEER) the dehumidification qualities suffers greatly.

    The new furnace may have a 3.5 ton blower where the old furnace might have been a 4 ton blower. But they would normally both be set to move about 3 tons of air. I don't know why you would notice a decrease in the airflow except for the coil being too close (if it is).
    Last edited by George2; 04-02-2013 at 04:29 PM. Reason: added a word

  6. #6
    Quote Originally Posted by wahoo View Post
    What type of furnace did you replace? Pilot light standard, 80% electronic ignition, or +90%? What was the input of the old furnace? What is the efficiency of the new furnace? Can you post some pictures of plenum set up?
    The original was a Carrier 80% w/gas pilot, and the specs should be the same or better on the new one.

    Attached Images Attached Images     
    Last edited by aworkinprogress; 04-02-2013 at 04:38 PM. Reason: pics

  7. #7
    Quote Originally Posted by George2 View Post
    Is your furnace in the attic? The new slab coil is a 48,000 Btu, if I'm reading the numbers correctly. The new condenser remains a 3 ton? Slab coils are supposed to be mounted a minimum of 18" away from the furnace. You might check that. Also, when we mismatch a coil to a condenser (for the higher SEER) the dehumidification qualities suffers greatly.
    The new furnace may have a 3.5 ton blower where the old furnace might have been a 4 ton blower. But they would normally both be set to move about 3 tons of air. I don't know why you would notice a decrease in the airflow except for the coil being too close (if it is).
    Yes, it's in the attic and the coil is 18" from the furnace. I was fine sticking with the "N" type coil because that's what the old system had (if it aint broke), but again, all the local "experts" kept saying the slab was better for controlling humidity. Hmmm?
    I don't think a lower price was their incentive because one place wanted more if I wanted the slab coil.

  8. #8
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    5,031

    Too Much Concern About SEER Levels...Can Lead To Comfort Problems

    That new 4-Ton coil probably has a lot of fins per inch which increases the airflow resistance & pressure drop, reducing airflow.

    For humidity purposes; why didn't they go with a 3-Ton coil which is easier to get colder, since the new 3-Ton condenser will have a smaller capacity compressor than the old 3-Ton condenser's compressor.

    Don't quite understand their thinking, unless they were simply thinking about the highest possible meaningless SEER number; which is NOT the important consideration in your high humidity situation...the highest latent load capacity ought to have been their primary concern.

  9. #9
    Quote Originally Posted by udarrell View Post
    That new 4-Ton coil probably has a lot of fins per inch which increases the airflow resistance & pressure drop, reducing airflow.For humidity purposes; why didn't they go with a 3-Ton coil which is easier to get colder, since the new 3-Ton condenser will have a smaller capacity compressor than the old 3-Ton condenser's compressor.Don't quite understand their thinking, unless they were simply thinking about the highest possible meaningless SEER number; which is NOT the important consideration in your high humidity situation...the highest latent load capacity ought to have been their primary concern.
    Well, that makes complete sense and confirms my suspicion about the coil being at the root cause.
    I believe the new system is 3.5T, so apparently that's enough of a difference ?
    What would be the best course of action to remedy this ? Should I have them replace it with a smaller "N" type?
    Last edited by aworkinprogress; 04-02-2013 at 06:00 PM. Reason: .

  10. #10
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,744
    You said in the first post that the new A/C was a 3 ton like the old A/C. A 4 ton coil with a 3.5 ton A/C make more sense, however, why did they enlarge the capacity? Thank you for the pictures.

    It appears that the duct transition from the furnace to the coil and the supply duct on the other side (of the coil) does not completely cover the opening of the coil.

  11. #11
    Quote Originally Posted by George2 View Post
    You said in the first post that the new A/C was a 3 ton like the old A/C. A 4 ton coil with a 3.5 ton A/C make more sense, however, why did they enlarge the capacity? Thank you for the pictures.
    It appears that the duct transition from the furnace to the coil and the supply duct on the other side (of the coil) does not completely cover the opening of the coil.
    Sorry, I meant both were 3.5T. They were able to send a Tech out today,and after poking around he said the furnace was wired for a two stage set up rather than a one stage, so it was only operating at 60% output from the blower.
    It's now blowing and sucking harder than before, but it's not hot enough right now for a true test,so it'll have to wait until the weekend when the temp creeps back up. I'll see where this goes and post back.

  12. #12
    Quote Originally Posted by aworkinprogress View Post
    They were able to send a Tech out today,and after poking around he said the furnace was wired for a two stage set up rather than a one stage, so it was only operating at 60% output from the blower.It's now blowing and sucking harder than before, but it's not hot enough right now for a true test,so it'll have to wait until the weekend when the temp creeps back up. I'll see where this goes and post back.
    Ok, back on point. The next weekend it was finally warm enough for the system to kick back on but it started making a humming sound at the return ? Hmmm, didn't do that before the re-wire,so another Tech came out on Monday and it sounded like he wired it back to the original setting, and then back to the "high" position.
    He determined it needed a heavier filter to quiet down and that did the trick and it was ok for the moment.
    The weather cooled down again, so it didn't come back on until yesterday, but now I noticed that the thermostat is not reading the actual room temp, so if I have it set at 75 deg it's not turning on until the actual room temp is 78 !!
    When it comes on it's reading the room temp at 76, so it cycles once to get back to "75" which is actually 77, so it's still hot, and now it doesn't feel as if it's cooling as well???
    I'm, thinking the thermostat (Honeywell TH8000) is the culprit ?
    I checked the coil and it's not frozen, in fact the air in the chamber doesn't feel all that cold?
    Ugh, this is really frustrating and I do appreciate all the input I've received thus far.

  13. #13
    Join Date
    Aug 2012
    Posts
    2,750
    I'm thinking you have a freon shortage did anybody check the charge as in superheat and subcooling? Static pressure needs checking also as well as fan speeds.
    My name is TooCoolforschool and I am a chronic over charger.

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