AC air flow problem SOLVED

[ChopperBill]

Gary, the very first page of this topic has some pictures. I was kind of unsure until I took the grill off of the air conditioner. Then I could see just what is up and how the "tent" will get air flowing in the right directions.

 

[jimtoo]

Gary,, go to the first page of this thread and scroll down to the 7th post, it will be from timk. He has provided pictures and a detailed drawing. It does work.
Jim

 

[bowtorc]

jimtoo

I THINK IT WAS A FREEBIE FROM A GREAT DEALER

ROGER

 

[jbeletti]

Added the "timk" tent in my AC plenum

Hi all,

Last Thursday night, I did timk's tent mod in my main AC plenum. Took me about 2 hours. I will add more pics later.

I would "estimate" that I increased the airflow from the AC vents by nearly double.

I started out with a 4" x 24" round galvanized furnace pipe. I flattened it out, then cut out an initial piece 19" long x 5" wide. I then trimmed that to 3-3/4" wide. Then I made all my bends to trial fit it. It was too short. I added on a bit more length (using foil tape for the addition), fitted it and used a few screws to hold it in.

The way I made mine, I have eliminated the effectiveness of the chill grate as my mod is the full width of the opening so little air makes it to the chill grate when opened.

Thanks timk!

Jim

 

[ChopperBill]

Great pictures Jim! When I did mine I kind of slop @$$ed it in and it made a HUGE difference. I was going to make mine a little more professional but thats when I fell off the ladder when it broke! Have a new ladder now and when the Bighorn gets back from the dealer I will attend to it.

 

[Ken Washington]

I must be the only one to try the Timk Mod and found that it did not help very much! At best maybe 5 percent more air flow. I will say that it was a little quieter but since I have the second A/C, I decided not to leave it in. It was worth a try though!
Ken

 

[jbeletti]

Ken,

I still may end up buying an anemometer to determine the change in velocity and temperature at each duct with and without the mod. My 2x flow is just my sense and could be off.

Like you, I did notice that the unit is quieter running. And that's a good thing.

I wonder if you have a different brand/model than I do? I have the Dometic 15k unit.

Jim

 

[Ken Washington]

Jim, We have the same unit but Bill Plemmons has worked on mine twice and added more ducts in main living area. With the second A/C, I changed the vents in the bedroom to the type that can be closed which increases the flow in main living area. All of my duct work looks real good with edges smooth unlike some pictures of others that I have seen on this fourm.
Ken

 

[timk]

I must be the only one to try the Timk Mod and found that it did not help very much! At best maybe 5 percent more air flow. I will say that it was a little quieter but since I have the second A/C, I decided not to leave it in. It was worth a try though!
Ken

Ken,

We tried the mod on our kids Thor 5er over vacation this summer. It didn't work very well either. After some inspection we discovered his vents were almost smashed closed. So there was no place for the air to go.

You might get a mirror and take a look down the ducts.

TimK

 

[Ken Washington]

TimK,
Wanted to let you know that we don't have an issue with air flow. I was just trying your mod to see what effect it would have! I can fill air flow sitting down in the chair and in other places in the unit. We are very happy with everything now and looking forward to going camping!

 

[Uncle Rog]

Howdy, I was going to try the timk fix, however when I repaced the front crank vent with the 13.5 btu unit I sealed off the forward vents with paper and duct tape. I then ordered some closable replacement vents. When I removed the old vents the flow was at least double the volume than before, go figure. I guess the extra pressure opened something up.....

 

[trdeal]

TimK,
Just playing around this afternoon with a piece of cardboard attempting a diverter for the ac. Trying to get a pattern for the sheet metal. The diverter made a huge difference in air flow to the off door side vents. I have not done the finish job yet. Before I buy anything , did the diverter work well for you during the hottest days of this summer? Did you only use the foil duct tape or did you use sheet metal. I had a hole that was not sealed in the cold air vent,which I sealed, and a piece of roofing material flapping in the intake, which iI also taped down. Thanks for the info

 

[timk]

Terry,
The fix is about air flow. It does help in the hottest days, by increasing the amount of air that gets out of the duct work. But there have been days that I still could have used a second ac unit. Under a 100 its pretty good, but get over a 100 its just hot.

You can use just about any pc of metal, from a soup can to beer can. It just needs to be big enough to smooth up the air flow. But you do need to get a roll of foil duct tape, to hold it all together.

TimK

 

[trdeal]

Thanks. I am going to work on it this week. The wife and I have been talking about the second ac, But the only place we could use it would probably be at the beach,because of the power situation at the campground we camp at near our home. We are at the beach now only 1-2 weeks in the summer so we are having a little trouble justifing the expense. We have made it pretty good the last couple of years at the beach by keeping the day-nite shades pulled down, ceiling fan on and the ac set as low as it will go. The campgrounds we normally camp at have plenty of shade and we don't really need the second ac. Thanks for the info.

 

[shaneandtammymoore]

air flow problem

Some more tips I have found. I have been working on mine for a week now. The TimK mod helps a lot. I also got to studying my vents. I pulled the diffusers down and found out that the main duct goes way past where the vent is. The main duct in the bedroom went past the vent 22 inches and the ones in the Living area were about 14 inches. Just cooling dead space for nothing. I have taped all that off so that the end of the line is at the last vent. I took pictures but they were not very good. It has made a huge difference in my airflow. If anyone needs more info or help let me know and I will see what I can do with explaining and/or pics. This little mod along with TimK's was well worth it in my unit. Maybe $8-$10 in materials. Tape and a piece of sheet metal. Much cheaper than a second A/C.

 

[Wild Wind]

The duct work in any forced air system is suspose to extend pass the last vent. By blocking off the duct you have unbalanced the system, have forced most of the air to exit the last vent, causing a lost in back presure, used to balance all the vents.
Hartland actually has designed a fairly good duct system, but as usual, it is their poor workmanship causes the system not to work wright.
The air conditioning system one of the few things, that has actually worked petty good on our fifth wheel. It has especially worked well since I used the "Great Stuff "foam, See my earilier post on "Great Stuff".

 

[DennisZ]

The real answer

I just found this Dometic Installation guide for ducted roof mount air conditioners. According to the manual, there should be a MINIMUM of 4 registers per run (Read that 8 total to a max of 12 total registers). Since my unit only has a total of 6 (3 per run), and I think most of our units have only 6, it seems like the answer of putting in more register is part of the correct answer.

WildWind is also correct in that the manual states that there is a minimum and maximun length from the last register to the end of the duct (5" to 8"), I think many of ours are past this limit.

You may alos find other interesting info in the manual.

 

[shaneandtammymoore]

a/c

DennisZ,

Some awesome info here. Great link. Saved it to my laptop. My dealer has agreed to add more vents to my unit since I also have 6 total, I may add even more now that I have this info. As for the end of the run, I am going to leave mine taped off and try it when it gets hot here again. 22 in. is a little more than 5-8 in. Thanks for the info.

 

[khd995]

Many of you have mentioned getting into the ductwork. Checking to see if the duct is smashed, etc. How do you check the duct work. Is there a way into the roof. How do you find all these holes, etc. to cover.

 

[tdharley]

a mirror & flashlight