A/C ductwork: Six or 1ns did you check?

[Roll]

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

[cfsoistman]

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.

[Roll]

Originally Posted by cfsoistman

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

[1nshort]

Originally Posted by Roll

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.

1NShort

[Roll]

Originally Posted by 1nshort

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?

[garbonz]

I love pictures... PLEAASE

[cfsoistman]

Originally Posted by Roll

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.

[garbonz]

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.

[1nshort]

Originally Posted by Roll

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.

[cfsoistman]

Originally Posted by garbonz

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.

[Tiggerdad]

The Crusader 330MKS is a single duct system for the A/C in the kitchen and living area. If you install a second A/C in the bedroom, it will only blow down and not through the ducts. The A/C in the kitchen sends air out via the duct work to the entire RV.

[garbonz]

took a look at my system today and it is retarded, No thought to distribution or air flow. the drivers side duct goes from the AC unit rearward for ten feet and has one outlet. since the squirrel cage is on that side that duct get all the flow. the curb side duct goes all the way forward and has 3 outlets with the further one getting almost NO flow at all. I think I can get better flow to the bedroom but only by restricting the flow to he living room outlets.

I understand why the AC systems re having problems getting consistent performance throughout the coach

[go6car]

I'm a bit late to the party here (been a heckuva month!)

The whole trick for us has been to get both ACs up and running EARLY in the AM, to keep everything cold all day/night long. So far; so good. What's bugging me more is no way to shut off the passenger vents in the dash - can only "deflect" the air. Grrrr......

[Roll]

Originally Posted by go6car

I'm a bit late to the party here (been a heckuva month!)

The whole trick for us has been to get both ACs up and running EARLY in the AM, to keep everything cold all day/night long. So far; so good. What's bugging me more is no way to shut off the passenger vents in the dash - can only "deflect" the air. Grrrr......

I have two different types of cab/dashboard A/C vents.

The ones on the drivers side can be closed by pushing the deflectors flat. The ones on the passenger side are different, they are solid inflexible balls that you twist within a "socket" to direct air flow.

I do believe you can close them by rotating the ball so it faces directly into the side of the socket it rotates in.

Maybe a better way to describe it is to point the open end to a position 90 degrees from straight out/wide open. I am fairly certain you can block the air flow. I'll be fussing with the coach today and double check that, I may be wrong.

One other thing to keep in mind... Even if you get the "balls" rotated to block air flow you may still get cold air from the open duct that is attached to firewall and points right down to your feet. It has no deflector, its just an open black plastic pipe.

Normally this would be for heat only but I'm not so sure the HVAC system in the dash board is entirely efficient or that it functions as well as you would expect in an automobile. They all seem to be just a bit ad hoc and they seem to suffer problems frequently; at least based on the numerous posts about problems with dash A/C-heat I've seen.



Roll

[go6car]

Roll - I have the same configuration as you. Wish they would have just put the same type of vents on the passenger side. Our dash air is really STRONG!

Haven't found a way to close off the passenger vents, just deflect out to the sides so it's not blowing directly on me. I'll take another look this week to see if I'm missing anything there. So far, haven't noticed anything leaking out of that foot vent (thank goodness!!) as I hate cold feet!

All this AC talk is making me sweat, LOL! I'm hot has heck right now - new house AC has a Freon leak somewhere that started last night. Of course these things never happen on weekdays during normal business hours.