Just starting to do my research and getting the wheels in my head turning... lol.
I don't think I'm going to have much luck trying to redesign or heavily modify the existing Coleman 15k unit. There's simply too much wrong with it. haha. Dometic did try to optimize the basic RV roof air design, but it's still a pretty primitive unit that only really works well in a certain set of conditions. Poor airflow, weak/cheap compressors, small condensers and evaporators without enough tubing passes and finally the capillary tube limitations are just too much to overcome. I could replace the capillary tube with an expansion valve, but I'd still have the other problems. I could increase airflow through the condenser and compressor area, but the static restriction of the capillary tube would still hold back any increases in efficiency. I could increase the compressor output, modify the capillary tube and tweak the refrigerant volume for better cooling, but still have the undersized evaporator that would hold back any other improvements.
So basically Coleman did "OK" with the dirt cheap components and design they've used for 4 decades. After all, it probably costs them around $100 to build one of these units that retail for between $500-$700. Why bother changing it when they're probably selling all of them they make?
This is how far out of the box I'm willing to go... haha...
https://www.pioneerminisplit.com/col...ystem-full-set
So far in my trying to figure out a solution for our coach, this looks interesting. Unfortunately we're limited to 110 volts in our RV's, otherwise I'd be looking at 220 volt systems. But look at the design- little things like brushless motors. Wow! Hey Coleman- try jumping into the '90's and embrace brushless motor technology! Geez.
I should probably add a little basic physics lesson to all of this discussion. All we want in our RV's is cool or comfortable air when it's hot outside. To do that, we need to REMOVE heat. That means we're going to be creating heat to end up with cool. I know that's pretty basic, just thought I'd start simple.
That's why what I mentioned about stationary RV's vs. moving RV's is a big deal. Removing heat is way easier if you have access to basically "free" 60mph airflow. The design of these roof AC's doesn't take advantage of it in any way.
The next basic principle is the system has to control the pressures in the condenser and evaporator to efficiently remove the most amount of heat. You can either do that by cycling the compressor, changing an orifice/valve or simply making the system work without any feedback or control whatsoever. The final example is what we have on our roofs.
The output is fixed. Which btw is why the thermistor/probe mod to move or remove it does nothing.
IF it was an expansion valve or cycling clutch system, it
WOULD have made a difference. It's not.
So now that you understand that, look at what these ductless split systems are doing- They have brushless compressor motors! Wow, like I said, welcome to the '90's. lol. So to control evap and condenser pressures, they simply speed up or slow down the compressor. That's huge.
Anyway, I hope some of you guys learned something so far. haha. I'll keep thinking and researching, then I'm gonna order something and start modding. Yikes! I'm excited because I know there's a TON of room for improvement on what's been the same old cr@p they've been putting in RV's for decades.
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