A/C Condenser Under Rear Cap

[lovetofix]

As mentioned in another thread I am brainstorming about the A/C condenser location in my bus.

I can't do roof A/C units with the twelve inch roof raise it has.
Also the PO of my MC9 stuck a window A/C unit through the back cap so I am considering having a custom cap made that would square the back up and then use that space for two or even three condensing units.
I would first build a waterproof bulkhead and floor above the radiators to eliminate any ingress for water and provide support for mounting. The new rear cap/removable cover would have side (and maybe top) air inlets and rear outlets. Because of the extra 12" of height I have plenty of room to work with above the radiators.
I know I could just get the fiberglass rear cap patched and put the condenser somewhere else but that would pretty much force me into a 240volt single condensing unit with multiple evaporators. With that I loose ability to "easily" run at partial capacity on 30amp service and I would not have the redundancy of multiple air conditioners.
Any thoughts on feasibility, airflow, or other ideas in general?
Sorry I don't have better pictures!
I am thousands of miles away from my bus for a while. 


And you may feel free to just tell me I'm crazy! (Psst.. I already know)

[richard5933]

Didn't see your new thread so I answered on the other...Here it is again to keep it in the correct conversation...

Without a doubt the CC units were spec built to be mounted the way they were. I was just thinking that with the low cost of the mini-split units it seems like a good way to get all the components, even if they need to be recharged.

For a guy that has basic a/c skills and equipment, it's also possible to buy the components off-the-shelf to build one from scratch. An option that would probably allow for higher-quality components chosen for a spec built unit that would fit exactly where you want it.

I looked at a very early CC conversion built on a Flxible recently. The CC a/c unit had the condensing unit mounted in the space above and to the side of the engine in the rear cap. A vent was cut to provide air to cool the coil.

A/C units can be tucked in all kinds of places with a little creativity. Not saying you should do exactly was CC did, just trying to show some ideas as food for thought.

[buswarrior]

The challenge will be keeping them clean.

Everything that passes under the coach, gets swirled up onto the rear by aerodynamics. All the drips of oil, fuel, leaking anti-freeze, road dust and stones, all are stuck to the rear.

Always the measure, a clean rear after a day's highway use, proves everything is tight. A rare condition for many, many old buses...

That's why it is such an under used piece of bus real estate.

Happy coaching!
Buswarrior

[lovetofix]

The challenge will be keeping them clean.

Thank you, that is the kind of thing I need to hear from others experience.
I don't know much about aerodynamics but have a little understanding of general physics.
I was thinking if the rear cap/cover was  2" or so taller than the bus roof that it would catch enough air while driving to keep clean air moving through that whole space. My roof is smooth except for the emergency hatches  so there should be good linear air flow across the top of the bus. This would hopefully keep the coils clean and I can accept the extra wear it might put on the fan motors to have them freewheeling in the wind even when they are not running.

[DoubleEagle]

I would not count on a clean linear air flow across the roof. It will be disrupted by the deflection of air hitting the front of the bus. A wind tunnel test of a scale model would be a way to test what actually happens.

[luvrbus]

I would not count on a clean linear air flow across the roof. It will be disrupted by the deflection of air hitting the front of the bus. A wind tunnel test of a scale model would be a way to test what actually happens.

Maybe today I can get some photos of Brads 4107 ,he spent a lot of time on his mini split and it shows it is the cleanest mini split install I ever saw lol it had to be to match the best looking 4107 conversion I ever saw

[dtcerrato]

@ Luvrbus
With those kind of compliments, photos would be great!

[Jim Blackwood]

What you are concerned with at the roof would be called reattachment of laminar flow. You can find articles analyzing it by running a search. The flow will separate at the front and at the roof hatches and how much smooth distance is required to reattach will depend on airspeed. I don't know but I suspect you might be OK with your 2" scoop, however in any case the airflow will be a bit slower than vehicle speed due to microturbulence.

Jim

[lovetofix]

Pictures of actual installs would be very helpful!
I am not set on any particular plan. I like the idea of simple redundancy and using otherwise useless space. I've worked with my dad who installed HVAC for almost 20years so building a custom setup is not out of the picture, but mini splits are cheaper and more easily replaced down the road.
I want to learn what works and what has been tried and failed so I don't foolishly waste precious time and resources. But on the other hand I am not afraid of trying something new if the logic and supporting evidence is sound.
I don't think it needs a jet stream flowing through the the rear cap, just enough flow to offset the vacuum created by the back of the bus so road grime doesn't climb up through the rear vent openings.
I am a busnut! That is why I am here, so nutty is fine I just don't want to be stupid.

[richard5933]

Can you bring the air in from the side of the cap instead of the back of it? Would eliminate the negative pressure zone.

I posted photos of the Custom Coach units on the other thread. I can get you more if you need, but they are really built from off-the-shelf commercial refrigeration parts. I think that you can find pre-made condensing units which could be installed nearly anywhere with a bit of ducting for air flow.

[lovetofix]

Can you bring the air in from the side of the cap instead of the back of it? Would eliminate the negative pressure zone.

I would definitely have side inlets, I just don't know if they would be enough to equalize the pressure differential.  From the little I understand of aerodynamics the sides and top of the bus are also low pressure zones just not as low as the back end. I think the fans on the condenser will move enough air when they are running with side openings only, the concern is when they are off that crud is going to come up off the road and coat the coils.

[peterbylt]

Just in case you think it might be helpful, this is how the auxiliary AC that was in my bus was installed, It was done by Welsh industries in Ga.







Peter