Building a Micro-Split AC System


Engineer In Residence
Initial work on this subject is over here.

The short of it, I am trying to build a Split AC system in the ~5,000btu range. Limited space, cost, and running occasionally from battery power drove me towards building my own.

I am starting with a 5,000btu mechanical window unit.

I am going to cut in half approximately on this line.

Since the fan is shared between evap and condenser, I bought a used fan for the evaporator.

The plan is to put the compressor and condenser under the van in this space.

I have a pile of copper fittings and some refrigeration copper tubing. Hoping to get the sections separated today. Then I will fabricate some sides to rebox the two halves. The evap unit will also need a bracket to mount the motor.

Another issue is sealing the motor on the outside unit. It will be exposed to dust and moisture. Neither end of the shaft has a seal. One side can just be capped, as I will be cutting the unused shaft off. The other side is 8mm, I think there is room to glue a shaft seal to the motor housing, and then seal the wire penetration. That should eliminate issues with dust/moisture.

Recommended books for Overlanding


Active member
very cool - excuse the pun. Ive been thinking of doing something similar for the same reasons with a portable unit, so definitely interested to see how this works out

The Artisan

Depends on how much you run it. It uses about 450-500W running through an inverter.
I am looking at doing the same on my large flatbed pod. Looking at 2 tesla packs about 11000 watts and I have a Honda gen 2k. Great work


Depends on how much you run it. It uses about 450-500W running through an inverter. I am working on a way to run or at half speed for half the cooling.
Are the inverter losses significant? Are there no suitable options that can roof a house bank?


Engineer In Residence
Inverter losses are about 8% for this load.

You can do the math. The best units are between 2.5-4.0 coefficient of performance. That means for every 1 watt of input power you get 2.5-4.5W of cooling. So if you want 5,000btu/hr (1,460W) of cooling, you need about 1,460/3 = 486W of input power. There is no free lunch. Well, swamp coolers work okay in dry places, and they have very low power needs. The problem with them, is they are useless in places where the humidity is over 35%.

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Engineer In Residence
There are supposedly single phase VSDs, not sure how well they work. I am only familiar with the 3 phase variety.