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Old 07-23-2018, 04:20 PM   #119
gmtech16450yz
Senior Member
 
Brand: Thor Motor Coach
Model: Vegas 27.7
State: California
Posts: 289
THOR #10907
Quote:
Originally Posted by vegasruv24.1 View Post
I wanna add this,.. the objective here is,. one air exchange,.. and two exterior R value.. and three AC efficacy..
#1... they blocked off half of the return with the stock grille, that's why the DB is so high...

#2.. putting the bubble insulation in the windows ups the R value and does the most... even in the shade...


#3 to get the most out of the AC, you need to have the right amount of return and service ducts...in stock form, they suffer..



Nice! Short and to the point, unlike my posts. haha.

BTW guys, during my 3 days in 100 degree heat we had bubble insulation in every window and foam pillows in all the vents. I'll post some pics of temp readings below.

Vegasruv, do you have an amp clamp? That's a really good way of judging restriction to airflow in fans. Yesterday I messed around with the intake grilles, you're absolutely right, they're horrible. I had already taken the filters out of mine weeks ago after seeing how hard they sucked into the opening when you pull them away. One of my mod tries I'm going to do before I give up on this 15k is to redesign the intake and outlet grilles on the ceiling panel. Yeah, what a stupid design.

There is a number 4 that should go on your list above, but it's the part we have no control over which is why you didn't include it as "moddable". It's the actual compressor/evap/condenser/capillary tube part of this all. We can't do much of anything with all that except for maybe trying to change the length of the capillary tube. (Which I was considering but it would actually be easier to engineer my install of one of those residential split units than to open up the refrigerant side of the Coleman.)

The reason I mention that is because the more airflow into and out of the evaporator core, the higher the discharge temps will be. There's obviously a point where you get too much air for it to be efficient. The discharge temps on these units are already REALLY HIGH, you're not going to get down into even the high 30's unless your inlet air is below 60, which is pretty d@mn cold for air conditioner use! The evap anti-freezing probe/thermistor is actually kind of pointless with the way they run the evap pressures so high. A well designed AC should be able to keep the evaporator temps just above freezing even at high fan speeds in high ambient temp situations. These Coleman units don't run anywhere near freezing even when inside coach temps are a cool 70 degrees.

My point is that it's a good idea to increase or optimize evaporator inlet and outlet airflow. Just monitor your inlet and outlet temps though because they might end up being too high because of the limitations of the rest of the hardware.

The mods I'm doing to give the Coleman 15k one more chance are these...

I'm adding 2 high cfm fans to the condenser box. The condenser fan/shroud assembly is truly a caveman design.

I can't turn the entire unit around to take advantage of 60mph air because it would mean swapping the ducting/inlet sides. boo.

I'm adding one or two vents to the grille panel on the outlet side.

I'm redesigning the inlet side of the grille panel to remove the bridge across the opening. (stupid)

I'm going to fill the voids around the evap core with expanding foam and improve airflow through the core/fan area.

I'm going to seal all air leaks around evap and condenser mounting/sheet metal. A fair amount of air was bypassing the evap fan. I'm going to "tune" the position of both the fans on the motor shaft for optimum airflow by using the amp clamp readings.

I'm going to clean up the horrible passageways from the outlet of the evap fan into the coach ducting. It's a mess.

Then I'm going to put it all back together and be done with trying to make a silk purse out of a sow's ear. lol.

On the subject of "Is it the AC units or simply the heat loss of an RV?", I totally agree with the heat loss side, but I know for a fact that these roof AC units are NOT VERY STRONG. The compressors are cheap and weak. The capillary tube system is cheap and grossly inefficient when out of it's optimum range (which is constantly, the way Coleman set up the sizing of the tube). The only thing I can say about these roof AC units is they have excellent airflow through the evap. The delivery side of the fan system is very strong, and with 1/3hp behind it, it takes a lot of restriction to slow it down. It's just too bad they didn't push the compressor/capillary tube/evap and condenser cores further to exploit that airflow. A stronger compressor, with an expansion valve system going through evap and condenser cores with more tube passes would make these units more than capable of cooling even big RV's. That would cost more to make though and cut into their profits greatly.

Hmmmmm, sounds like Thor's business model! Build them fast and cheap and don't worry about what happens after the sale. Welcome to America. We've learned well from the Chinese.
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