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Old 07-10-2013, 07:14 AM   #1
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A/C ductwork: Six or 1ns did you check?

Remember the posts about the ducting for our A/C units?

Did you ever check to see if it is all one set of outlets connected to a single duct run?

I ask because I want to know if my unit is different than what you have,

To reiterate; if I turn on one A/C unit I have cold air coming out of all of the outlets even those on the far side of the second A/C unit. Of course the farther away from the unit that is running the weaker the air flow but in my coach they are all connected to the same ductwork.

Is this like your coach?

Thanks,

Roll
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Old 07-10-2013, 07:32 AM   #2
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I believe all the motorhome ducting is similar. The ducts run front to back and are shared by both AC Units. So not matter which one is running the air will come out all of the ducts unless closed. I installed foan rubber at the last registers on each duct front and rear. The duct runs pass them all the way to the front and to the rear. By installing the foam rubber it shortens the length of the run and doesn't rely on extra pressure for air to leave the ducting.
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Old 07-10-2013, 09:03 AM   #3
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Quote:
Originally Posted by cfsoistman View Post
I installed foan rubber at the last registers on each duct front and rear. The duct runs pass them all the way to the front and to the rear. By installing the foam rubber it shortens the length of the run and doesn't rely on extra pressure for air to leave the ducting.
Not sure I understand what you did, how you did it and how that gives you better service. I would like to know; can you elaborate?

Roll
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Old 07-10-2013, 07:31 PM   #4
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Quote:
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Not sure I understand what you did, how you did it and how that gives you better service. I would like to know; can you elaborate?

Roll
Roll,
All ducts are connected to the AC units. Those that are closest to the unit (at the end near it) have high flow due to the dead end (nowhere for the air to go but down). Those at the far endhave better flow too for the same reason. In between the flow coming out is weak. Here is why, I put a fow strength monitor uup into some of the ones in the center (you can also stick a finger up there and feel it), the flow is strong. There is nothing to force the flow downward so most of it goes past and some makes it out. I made a deflector with a 60 degree down angle on it about 1/3 the width of the duct which forced more air downward and out. This increased the outflow significantly. I plan to refine my deflector and install a few more, also will play with a couple different angles.

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Old 07-11-2013, 07:40 AM   #5
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Roll,
All ducts are connected to the AC units. Those that are closest to the unit (at the end near it) have high flow due to the dead end (nowhere for the air to go but down). Those at the far endhave better flow too for the same reason. In between the flow coming out is weak. Here is why, I put a fow strength monitor uup into some of the ones in the center (you can also stick a finger up there and feel it), the flow is strong. There is nothing to force the flow downward so most of it goes past and some makes it out. I made a deflector with a 60 degree down angle on it about 1/3 the width of the duct which forced more air downward and out. This increased the outflow significantly. I plan to refine my deflector and install a few more, also will play with a couple different angles.

1NShort
How did you install the deflectors and what do they look like?

Did you pull the round grills out to do the installation and at which locations?
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Old 07-11-2013, 12:56 PM   #6
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Old 07-11-2013, 01:13 PM   #7
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Not sure I understand what you did, how you did it and how that gives you better service. I would like to know; can you elaborate?

Roll
I took some foam rubber I saved from the packaging of a computer. Cut it down, removed the last register in the front and the last register at the rear on each side. I placed the foam rubber just beyond the opening of the register. This shortened each trunk-line, which is the duct, by more than 8 feet. So instead of [2] 37 foot long trunk-lines I reduced them to approximately 29ft each. So the air leaves the duct right at the register instead of going past it to pressurize useless ductwork. This actually helped the airflow of the other registers as well.
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Old 07-11-2013, 01:53 PM   #8
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The deadend ducts CANNOT effect the air flow, there must be a leak at the end or someplace else for the air to go that is not cooling the trailer. I spent years doing industrial ventilation and it can't be so. I could easily see the duct channels in these RV's being leaky tho and that shortening the leaky channel would have a positive effect. If air is exiting that channel into the rest of the overhead, that would explain what you are observing.
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Old 07-12-2013, 07:28 PM   #9
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How did you install the deflectors and what do they look like?

Did you pull the round grills out to do the installation and at which locations?
Pictures will have to wait. Took the MH to dealer for repair. The driver side slide moans and groans when starting to go forward and slowing, also a bit while driving at speed. The result is that the seam where slid meets coach, has a vertical stripe where paint is worn off, front and back. Boat-n-RV supposedly fixed it Jan-Mar, but alas no. It took only two camping trips and it was as bad as ever. Contacted Coachmen, they had me bring it back to the dealer and tell the dealer to contact them when they ID the problem......we'll see.
For the deflector I took some light aluminum sheet (like gutter metal) cut it with 3/4 inch surface contact and used 'goop' to anchor it, deflector angle is about 60○. Works but I am going to experiment some more only did a couple near center of coach between the two units.
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Old 07-12-2013, 08:01 PM   #10
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Quote:
Originally Posted by garbonz View Post
The deadend ducts CANNOT effect the air flow, there must be a leak at the end or someplace else for the air to go that is not cooling the trailer. I spent years doing industrial ventilation and it can't be so. I could easily see the duct channels in these RV's being leaky tho and that shortening the leaky channel would have a positive effect. If air is exiting that channel into the rest of the overhead, that would explain what you are observing.
I just created shorter ducts by using foam rubber. I have 1 register off the rear AC Unit that is on the driver's side trunkline. It's the only duct on the trunkline to the rear, but the duct continues all the way to the rear of the coach which is still 5 feet away. Up front on the same side the last duct is 6 feet from the front of the coach. That's 11 feet of ductwork without a register, just a blanked off trunkline. I know the air comes out from that register better than before because it now has no other place to leave. Velocity is stronger due to less back pressure being reqired to fill that unnecessary length of ductwork. As for leaky ends from the factory could be a possibility. I'm in the HVAC business and have been so since 1976.
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