Am I smart enough to DIY engineer an A/C system? (subtitled: turn my van into a fridge)

In the process of building the van into a mini camper, I've been thinking about A/C for when I'm hooked to shore power.  There are several super simple solutions, but what fun is that?  I could get a portable A/C and put it between the front seats and make a window template for the ducting.  I could remove one of the back windows and replace with plywood and cut it for a window unit.  Those obviously take up space... either real estate or visual.  The thought here is that I want to have a ready-to-go setup since my job takes so much of my time.  I don't want to have to spend a day "converting" my van to a camper when it's a lumber-hauler on Friday and I want to be lighting a campfire 50 miles away on Friday night.

Then it hit me that there is going to be a small cavern of space behind the rear trim panels in the back when I'm done.  I was thinking if I had some refrigeration unit - fridge, A/C, dehumidifier, etc - with serviceable parts, could I reduce it to its components and install it?

I've seen lots of cheap residential stuff with no service ports or really junk components, but restaurant liquidation auctions consistently have commercial fridges, freezers, mini splits, dehumidifiers, etc that I would assume have robust components and serviceable things.  I bought a commercial beverage cooler for $27 about 10 years ago and it's still running strong, and also has service ports and pretty universal parts like the compressor and thermostat.

The other thought is (after copious tutorial videos and lots of maths) to purchase individual components; compressor, condenser, evaporator, fan and be able to assemble something that works.

Can a plebeian smart guy learn what I need to know to pull this off? The compressor and plumbing is the easy part.  I think the real learning curve would come from sourcing the evaporator and condenser that works for my space and is the right size.

Maybe you could use some or all of the existing AC system? I would look at plumbing a parallel compressor into the system that you could run off a 120V. Or, could you spin the compressor on the van with its clutch disengaged somehow?

A battery charger and a switch to kick on the condenser fan would finish the system.

I see lots of RV's with  units similar to this mounted on the roof.

What about the evaporator and blower setup from the rear of a minivan? It's already pancake shaped and would fit behind your trim panels. Pick a compressor that uses r134a (lots of small older units did) and you don't even need to worry about the gas compatibility. 

I'm sure you could do it.  Figuring out how best to run the compressor quietly would be the hardest part, the rest is basically plumbing and getting the weight of the refrigerant correct.  To drive the compressor, a brushless motor?

In reply to jharry3 :

Rooftop unit seems like the easy button to me if you don't need a low roof height for clearing parking decks.

The easy button would totally be to cut a 14x14 hole in the roof and mount a Dometic unit up there.  You can get them used for a couple bills and they'll freeze you out in a space like that and if you add the heat strip, they'll do a pretty good job of keeping you warm.  But it would add about a foot to your overall height unless you spend more for the low-pro version. 

Building out a system from components seems like it wouldn't be too crazy of an idea, though.  You might even be able to take a unit like that or a cheaper window unit and disassemble it, assuming you can find someone to vacuum it out and then re-fill it.  I think the big challenge would be finding a place to mount the condenser and compressor in a place where they aren't radiating heat into the van.

EDIT:  Another option for something van-sized, if you wanted to use a rooftop, would be to get one of the units they put on pop-ups.  Since they're lower BTU units I think they can work on a 15A circuit instead of needing a 20A, and they're in less demand so they're cheaper.

I know it's not as exciting but my Express van with some modest insulation and a Maxxfan in the roof is very livable up to 95°F outside temps, especially if you can park in the shade. With the sun shade on the windshield and the windows blocked off with reflective insulation it will stay under 78 during the day and once it cools off at night I reverse the fan to blow in and bring in cooler air. 

Roof A/C won't work due to roof rack.

My van actually has rear air from the factory.  It's somehow magically a single system.  It shares refrigerant from one compressor with the dash unit.  I thought about maybe cutting the lines and isolating them, then finding a refrigerator compressor to run the rear air, but two problems with that - 1) finding the specs on the factory system so I can source compatible parts, and 2) if I do that, then I have no rear air for when I'm not camping (e.g. hauling people, or really hot days when I need the extra BTUs)

Mr_Asa said:

I'm sure you could do it.  Figuring out how best to run the compressor quietly would be the hardest part, the rest is basically plumbing and getting the weight of the refrigerant correct.  To drive the compressor, a brushless motor?

I would use a compressor like from a fridge.  They're pretty quiet.  Like this:

wae said:

Building out a system from components seems like it wouldn't be too crazy of an idea, though.  You might even be able to take a unit like that or a cheaper window unit and disassemble it, assuming you can find someone to vacuum it out and then re-fill it.  I think the big challenge would be finding a place to mount the condenser and compressor in a place where they aren't radiating heat into the van.

Thanks for the confidence boost.  I would plumb the hot side down through the floor to a condenser/fan mounted to the frame most likely.  There might be room to put the compressor down there as well.

In reply to Curtis73 (Forum Supporter) :

I really doubt that will have enough power to cool the van.  A large metal box compared to a small insulated box and all. 

dculberson said:

What about the evaporator and blower setup from the rear of a minivan? It's already pancake shaped and would fit behind your trim panels. Pick a compressor that uses r134a (lots of small older units did) and you don't even need to worry about the gas compatibility. 

I like that idea.  Pre-packaged, just add my own compressor

In reply to alfadriver :

They make them in all sizes, and they can turn the little box into sub-zero temps.  I have to think that there is some combo that can make my van 72 degrees.

Edit:  If you think about it, a tiny 8000 btu window unit has a compressor not much bigger than two of your fists and it can cool an entire room in a house.

Curtis, I have every confidence that you could take an old commercial fridge, carefully extract the compressor and condenser and evaporator coils, and transplant the entire thing into your van. Enlist a small fan to blow air over the evaporator coils and direct the air to the right places.  You'd be the coolest kid on the block.

Curtis , if anyone here could do it , you would be the guy  :)

what  are you planning on outside temps and humidity?

and how much of your interior space can you give up to mount the components?

In reply to 1988RedT2 :

if I can find a unicorn that runs R134, I already have the equipment to charge it myself

californiamilleghia said:

Curtis , if anyone here could do it , you would be the guy  :)

what  are you planning on outside temps and humidity?

and how much of your interior space can you give up to mount the components?

I'll get a picture for reference a little later, but the verbal description goes kinda like this.

On the left in the back, the trim panel covers the rear A/C and the gas filler neck, so the trim panel mostly comes out parallel with the wheel well.  On the right, there is nothing except the jack storage in the rear corner, so that trim panel hugs the outside wall/fender.  I plan on removing both sides and fabbing a steel-framed, plywood-skinned sides to which I can mount e-track which can serve as tie downs for cargo and maybe a couple load bars that I can set a bed platform on.  So the right side will have plenty of space to play with.

Curtis73 (Forum Supporter) said:

In reply to 1988RedT2 :

if I can find a unicorn that runs R134, I already have the equipment to charge it myself

Would it theoretically be possible to install such a system without opening it up?  If it was a working fridge, it would be a working cooler, running whatever refrigerant was in it.

How much space do you have under the floor? Could you do a basement air system like I used on SanFord?

Or if you have some extra scratch, one of these. 12 volt, but only about 1500 btus. It would probably keep you coolish at night but probably not during the day unless you were parked in the shade. Not cheap at $800+  Link.

Whatever you do, purge the system to the Nth degree before converting to an electric compressor.  Conventional oil is conductive and will destroy your compressor almost immediately.

So a quick drawing:

The red lines indicate my plywood boxing that I plan.  That should save room on the right behind the ply for a small, sealed 8" sub, any AC I add, plus maybe a little room for a cabinet that holds stuff like jumper cables, hitch inserts, and tie down straps.

This all saves me 52" between the wheel wells so sheet goods will still fit, and I can throw some e-track in it.

In reply to 1988RedT2 :

I suppose, but it would likely have to start life as an A/C window unit or portable unit.  I can't imagine if I pull a fridge apart that it would be suitable.  The condensers on those are usually large and flat, as are the evaporators.  I would rather have something like an A/C unit with "radiator" style heat exchangers that can blow-through.  I suppose it's possible I could use a window A/C and install something like this below to vent the hot to the outside.

Couple few options:

• Wall mounted window A/C unit.  Flush it into the interior as much as you are comfortable with.  Will only run on 120VAC and will need some sort of drain to the exterior.  Most I have seen come with a little cover for when you are running down the road to keep debris off the fins.  Look a the super duper little cheapo (RPods, etc) RVs for more of this style and a source for parts.
• Existing rear air evaporator plumbed into new 12VDC compressor.   You would need to fit a separate condenser and fan unit on the exterior of the vehicle but these are not too hard to source.  Could be operated while you are running down the road as long as your alternator has enough nut to keep the compressor running.  Overall drag on the engine would be a little worse because you are converting rotational energy to AC to DC to rotational energy to compressive force again vs just rotational energy to compressive force.  You would need to source high/low pressure switches, maybe an orifice or expansion valve, etc, but all that stuff should be doable.  You would have to do some math and calculations to figure out the correct or close enough to correct condenser and compressor needed for your system but the good news is as long as you are using R134a in your calculations, it doesnt matter who's math you use and the residential guys are pretty sharp on this stuff.  An HVAC jerk could likely help size your junkyard evaporator.
  • https://www.guchen-eac.com/what/low-voltage-electric-compressor/ld20a12ab-12v-dc-mini-refrigeration-compressor.html
• New stand-alone rear A/C system.  Look at what semi trucks run and buy one of those.  Can either be ducted or ductless.  The bulk of the items will end up mounted inside the cab but the location is reasonably flexible.  You can mount them on the floor or the walls.  

If I was designing an A/C system for a van that can be run on shore power, I would go with a 12VDC system and then power it off a large battery charger like a Redarc unit and draw from a battery bank.  The advantage I see to this is a few.  Firstly, you can in theory run for at least a little while on house batteries depending on other electrical needs and how soon you will be able to recharge.  Secondly, you can still run on shore power and charge your batteries while you are plugged in.  Doesnt matter if its inefficient on shore power, its a drop in the bucket in the grand scheme of things.  Lastly, if your A/C is of the 12VDC variety, you can still operate it while the engine is running as long as your charging system has enough capacity, something that the mains powered A/C units do not offer.  If you already have house batteries, the only additional expense is the RedArc controller, which in my mind is basically a necessary item in a modern RV build.  

 https://redarcelectronics.com/products/dual-input-50a-in-vehicle-dc-battery-charger?currency=USD&variant=29494631727217&utm_medium=cpc&utm_source=google&utm_campaign=Google%20Shopping&gclid=CjwKCAjwm8WZBhBUEiwA178UnPEUYMmC0aLMnYrhcp-fbTEDTGf5OEfFxcW-nMO8KnZzPz26aeGRuhoCzxQQAvD_BwE

In reply to 93gsxturbo :

That's a lot of good stuff to consider.  I hadn't even thought about a 12v compressor.

Sounds like a lot of work to use the existing AC, but probably cheaper, and certainly takes less space than a redundant unit.

Edit:  Am I reading the specs correctly that it takes 100A?  I mean, that makes sense given that a similar sized residential unit takes 10-15A, but I'm not sure I want to engineer a 100A setup.  That's a lot of electrons to move.