Building a Micro-Split AC System

luthj

Engineer In Residence
Some have used these. Used to be available at Costco, but seems to have disappeared.

I took at a look at those. 8,000btu is a bit larger than I need. The real issue is the condenser is ~20" tall, which is not conducive to underbody mounting. The compressors are also 12-14" tall, which doesn't make for easy interior mounting once you include vibration dampening. Now I could get flexible hoses, and mount the exterior unit on a bumper swing out. But that's just a non starter for me.

We've been on trips in the spring when they spray the sufficant on the FS roads and end up with 1/4"-3/8" of mud that dries like plaster to everthing. The sufficant must be alkaline as there is electrolysis on all the aluminum.
My current plan is to mount the condenser centered left/right, about 24" behind the axle. The solid side will face forward. So the condenser and fan will be protected from the worst of it. I also have 11" plastic mudflaps on the rear. Depending on my experience, I may add shutters or slip covers over the side vents. I am also on the lookout for a corrosion inhibiting coating for the aluminum condenser fins. The pipes are all copper. Time will tell how long it lasts, but it was a cheap unit, so if the condenser corrodes out, I can probably swap for a similar unit. If it ends up working well I will just buy a used one to keep for spare parts.

IMG_20200714_131653625 by J Luth, on Flickr
 

Pntyrmvr

Adventurer
Up here in salt caked winter roads country we don't put anti corrosion spray on delicate aluminum condensers as the oil film reduces the efficiency. We just rinse with water and suffer!

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DzlToy

Explorer
dreadlocks said:
Would there be any way to just steal the compressor out of one of these and wire it up in parallel with the vehicles existing evap and condenser? or is the vehicles electric radiator fans too much wattage to make this reasonable? I'm wanting to install both shore power and engine powered AirCon into my Westy with its engine swap and since its gonna have to be all custom and I'd rather just have one condenser and evap to install.. I thought about just wiring up an AC motor on a custom bracket to a double clutch belt on the engine compressor but that seems rather Rube Goldberg.
There are several companies making auxiliary HVAC systems that tie back into the vehicles existing HVAC system. This lowers cost, save space and weight. One such product is called "E-Cool Park" and I believe several of the big players such as Dirna Bergstrom and Indel/Webasto offer something similar.
 

dreadlocks

Well-known member
Yeah I ran across a couple of those, I started down this path I think when I found the Webasto on a HVAC site when I was trying to find an heater core that was low power for a webasto diesel water heater, but just the compressors are extremely expensive.. This is not going into a Vanagon, but a Bay-window.. I've gotta fit a radiator to the nose, with fans/condenser, heater cores and evaps inside and the whole 9 yards.. so its gonna be a piece meal retrofit, the only thing I got to start with is the AC Compressor already attached to my TDI motor, at first I was just gonna delete it but then I decided having AirCon in this tin box would be worthwhile so its staying... with the poptop a rooftop unit pretty much off the table.

I just hadn't thought about trying to steal the compressor outta a cheap window unit, its not like I needa ton of BTU in that little thing and I could buy a half dozen window units for cost of the Webasto Compressor.. but I only know the basics about AirCon, I dont even have one on my house (Swamp Cooler here in Colorado).. I figured these compressors would be one way and a check valve would be unnecessary, but if not that should be fairly easy to address so I can have 2 compressors in parallel.
 

DzlToy

Explorer
In a perfect world, i.e. laboratory conditions, only 0.018 BTU per hour are required to raise the temperature of one cubic foot of air, by one degree Fahrenheit. Thus, a camper box measuring 12' x 7' x 7' only requires 263 BTU to heat the air inside from 50F to 75F.

In the real world, due to insulation, windows, solar radiation and the like, heating or cooling capacity must be significantly higher. I don't want to derail this cool thread, but spending a bit of time doing some basic heat load calculations, if you haven't already, may tell you a lot. I would hate to see a micro-split get built and installed only to find out that it is insufficient to cool the van, is loud or sucks power, once in.
 

luthj

Engineer In Residence
In a perfect world, i.e. laboratory conditions, only 0.018 BTU per hour are required to raise the temperature of one cubic foot of air, by one degree Fahrenheit. Thus, a camper box measuring 12' x 7' x 7' only requires 263 BTU to heat the air inside from 50F to 75F.

In the real world, due to insulation, windows, solar radiation and the like, heating or cooling capacity must be significantly higher. I don't want to derail this cool thread, but spending a bit of time doing some basic heat load calculations, if you haven't already, may tell you a lot. I would hate to see a micro-split get built and installed only to find out that it is insufficient to cool the van, is loud or sucks power, once in.
If you see the previous thread I linked in the OP, I ran this unit for a whole day (stuck through my front window) and monitored power consumption, noise, and performance.

I also think you might misunderstand what BTUs are. A BTU is a measure of energy (analogus to watt-hrs). Power is expressed as BTU/hr (analogus to watts) The energy required to cool 1 cubic foot of air has no bearing on the energy required to cool a space once you reach steady state. So that 263 BTU is whats necessary to cool that amount of air assuming no external heat transfer. That also does not include the thermal mass of any people or objects in the space to be cooled. If you had perfect insulation, then you would need 263 BTU just once. After that energy (heat) had been removed from the air mass, it would forever stay at 50F. Of course real world situations always have active heat transfer, and that transfer increases as the interior temp drops.

In any application there is a net heat transfer given the interior temp, exterior temp, sun, wind etc. So at 90F external and 75F internal a space requires so many BTU/hr to maintain temperature. In the case of my van 5,000btu was enough for 15-18F differential with 95F external temps, 70-80% humidity, and some direct sun.

In addition my primary usage of this AC unit is as follows.
  • Cooling my bed area (about 1/3 of the van space) for sleeping.
  • Keeping the entire van under 90F when parked with shore power (visiting relatives, transiting brutal hot regions).
 
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luthj

Engineer In Residence
It just barely fits between the floor supports.





There is a nice scalloped area for the spare tire clearance. It should provide enough space for exit airflow.

r

As you can see, it hangs down a little bit below the hitch. Should be far enough forward that my departure angle won't be affected.

 

luthj

Engineer In Residence
I welded on some quick-n-dirty brackets. 4 rivnuts into the floor supports should do the trick.





I did some measuring, and the evaporator will barely fit in my over-door shelf. I need to modify it a bit, but not a complete rework thankfully.

The next step is to figure out where/how to run the lines, wires, and drain. I ordered a few long sweep elbows for tight spots, but anywhere I would have to use them would be a tough solder location. I have some fiberglass cloth I can use to protect stuff.
 

Alloy

Well-known member
I took at a look at those. 8,000btu is a bit larger than I need. The real issue is the condenser is ~20" tall, which is not conducive to underbody mounting. The compressors are also 12-14" tall, which doesn't make for easy interior mounting once you include vibration dampening. Now I could get flexible hoses, and mount the exterior unit on a bumper swing out. But that's just a non starter for me.



My current plan is to mount the condenser centered left/right, about 24" behind the axle. The solid side will face forward. So the condenser and fan will be protected from the worst of it. I also have 11" plastic mudflaps on the rear. Depending on my experience, I may add shutters or slip covers over the side vents. I am also on the lookout for a corrosion inhibiting coating for the aluminum condenser fins. The pipes are all copper. Time will tell how long it lasts, but it was a cheap unit, so if the condenser corrodes out, I can probably swap for a similar unit. If it ends up working well I will just buy a used one to keep for spare parts.

IMG_20200714_131653625 by J Luth, on Flickr
Aluminum on copper is never a good combo.

You'll want to wash the condenser with alkaline neutral condenser cleaner. It will help to protect it but you need acess to both sides of the coil.....to make sure the fins are clear side to side
 

Alloy

Well-known member
It just barely fits between the floor supports.





There is a nice scalloped area for the spare tire clearance. It should provide enough space for exit airflow.

r

As you can see, it hangs down a little bit below the hitch. Should be far enough forward that my departure angle won't be affected.

That location looks like a prime target.
We regularily hit the hitch and mufflers on our Subaru. The mufflers are the same height and 12" ahead of the hitch.
 

luthj

Engineer In Residence
I found some low loss quick disconnects which should allow me to remove the unit for service if required.

Doing some quick math with R32 at 160 BTU/lb and needing 5000/160 =31.25 lb/hr. I should be good with 3/8 body for liquid and 1/2" body for suction. I will need to top the charge every 3-5 years, but service will be much easier.

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luthj

Engineer In Residence
Got the evap fan tested. I forgot to account for the foam seal pushing the fan housing down, so some adjustments were needed to stop rubbing.





Since I have a second fan motor, I need another 6UF starter capacitor. Also, with two motors I can now have the condenser fan turn off with the compressor. So I will move the dual starter cap to the outside unit, that lets me run only 3 wires between the two units (instead of 4 or 6). This does mean the evap fan will run only on high speed, which is fine with me. With no pressure or temperature feedback, this is the safest approach.

Once I get the fittings worked out, I can paint the housings and install in the van. Run the lines, then test and charge.
 
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