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  1. #1
    Join Date
    Jun 2003
    Posts
    16

    Hmm

    I have a 1973 mobile home. it is a double wide it is 1400 sq ft. and has a 4 ton coleman a/c unit 12" return. and 12" supply that y's to 2 10" that connect at the end of the trunk lines that is about 40' long one on each side of the mobile home the trunk lines are 10"x5" aluminum. 5 4x8 floor registers out of each trunk line. the problem I am having is only about 1 1/2 ton of air flow is comming out. so what I was going to do is change the return to 14" and then move the supply connections from the end of the trunk line to the middle so air flow would go both directions in the trunk and not have to only push one direction.(hopefully splitting the available air and being able to use more cfm from the unit) also i was thinking of making the return 14" connect to a "y" to 2 12 inch and placing one at each end of the home what is the maximum length of a return duct right now it is about 15' if i changed it to 2 12" it could be as mucch as 40' does this sound like it might help I do realise that this unit is oversized and i will never get 4 tons of air through that duct but that is the only thing I cannot change.

  2. #2
    Join Date
    Jun 2005
    Posts
    178
    your way under you might be able to go to 16 on the return and split to two 12s and 16 on the supply and go to 2 12 and you need to boost your supply to 2 14x10 and 5 4x10 registers that will get you close but it should be a little bigger you need a pro to come in and resize all of your ducts if you want it right but the above will get you at about 90% of air flow for that system.what you were planning on doing will do nothing but cost you money for nothing.

  3. #3
    Join Date
    Mar 2005
    Posts
    657
    Have you looked at the A-Coil. The original Coleman air filters aren't the best. Seems like a lot of people don't clean them or just remove them and don't put any filter back in. Seems like most of the problems with air flow I have seen is the A-Coil is really dirty. These are very easy to look at and verify. Since it is a 1973, and if it is the original A-Coil they are usually fairly cruddy by now.

  4. #4
    Join Date
    Jun 2003
    Posts
    16
    the 4 ton unit is a 1992 the coil has been cleaned and the a/c guy said i needed to change the supply to a 14 inch cause the 12 inch cant move enough air but i was wondering if the 10x5 ducts can handle the extra air or if i should connect the supply duct to the middle so the air will be split going both way's down the trunk

  5. #5
    Join Date
    Oct 2003
    Location
    southern mo.
    Posts
    323
    your on the right track,you want to keep your round duct as short as you can,is the unit at the end of the bldg.? if so you might wanna move it towards the center.how big is your return in the floor?check your duct work for restrictions and leaks,go to the end of the trunk and remove a register and put a good light in there,then go to the other end with a mirror.there are ways to add registers with the addition of a short piece of duct on the supply.

  6. #6
    Join Date
    Mar 2003
    Location
    Scottsburg, Indiana
    Posts
    356
    also if possible have these ducts ran in hard pipe. flexable duct in mobile homes tends to lie on the ground, this will give you better throw also.

  7. #7
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,753
    Connecting them in the middle will give you alot be air flow.

    As said above, shorter runs are better.

    If its a package unit design for mobil homes, it will have a higher static pressure blower, to move the air through your smaller ducts.

    Sounds like the installer didn't know what he was doing.
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  8. #8
    Join Date
    Jun 2005
    Posts
    178
    14 inch duct only gives you 1000 cfms and you need 1600 cfms 10x5 only gives you 200 cfms you need 800 to each side. 16 will get you real close with the return but 14 is only a little over 1000 cfms and 16 is 1800 cfms thats what you need for 4 ton to get close to what you need

  9. #9
    Join Date
    Jun 2005
    Posts
    178
    flex is fine to use if you hang it good to keep it off the ground ,if you use hard pipe you have to insulate all of it and its not fun. flex is already insulated you just cut it to lenth and put it up.

  10. #10
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,753
    Originally posted by coolcray3
    14 inch duct only gives you 1000 cfms and you need 1600 cfms 10x5 only gives you 200 cfms you need 800 to each side. 16 will get you real close with the return but 14 is only a little over 1000 cfms and 16 is 1800 cfms thats what you need for 4 ton to get close to what you need
    Not on a high static unit.

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  11. #11
    Join Date
    Jul 2004
    Location
    midwest
    Posts
    2,868
    Originally posted by beenthere
    Connecting them in the middle will give you alot be air flow.

    As said above, shorter runs are better.

    If its a package unit design for mobil homes, it will have a higher static pressure blower, to move the air through your smaller ducts.

    Sounds like the installer didn't know what he was doing.
    Yes, this unit comes with 12 inch supply and return openings and will handle the required CFM's because its designed to do this. Your only problem is the ducts being connected to the ends and not the center. Like mentioned earlier, you need to have the coil cleaned to make sure this is not part of the problem.

  12. #12
    Join Date
    Jun 2005
    Posts
    178
    the trailer is a 73 double wide which tells you it was probably sized for one unit in each trailer and now has one transplant which i probably a regular unit. i dont think the mobile home units enen have return ducts,they usally have a wall return oppisite the unit dont they.i think some one put a residential unit in.what model unit are we talking about.

  13. #13
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,753
    Coleman has been making units for mobil homes for longer then I can remember, and the return is in the floor.

    Go to their website and check it out.
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