Two air conditioners are better than one

Phoenix has had a Dometic FreshWell roof air conditioner since the conversion, and in the rear living area it does its job reliably — in summer it keeps a bearable temperature there even through midday. The problem is that Phoenix is over eight meters long, and the cooled air from a single unit at the back simply can't reach the front bed over that distance in sufficient quantity to make a noticeable difference there. At night, when you specifically need to sleep up front, this had long been the most noticeable compromise of the entire conversion.

The solution wasn't stronger fans or a better air distribution system, but a second, separate air conditioner for the front of the vehicle.

Where to put the second unit

I was looking for a place to install the second air conditioner so that it would cool directly overhead in the sleeping area, while not interfering with the already-finished wiring and interior. Above the front bed there was originally only a small roof hatch — without much benefit for light or ventilation, and at the same time exactly in the spot where the cooling was missing the most.

I replaced the hatch with the roof unit, so the second air conditioner didn't take up any new space in the interior — it just took over the position the hatch had already occupied.

Why an inverter, and why the SINCLAIR ASV-35BIS

I deliberately didn't go for the same type of unit as the rear Dometic. Classic ON/OFF air conditioners run either at full power or not at all — in the small space of the cabin, that means cold/warm cycles and a noisy compressor start over and over again. The inverter unit SINCLAIR ASV-35BIS, on the other hand, smoothly regulates output according to current demand, so at night it runs at low speed and noticeably quieter, instead of constantly kicking on and off.

For the front part of the vehicle, where you sleep, that's exactly the difference that matters — a quiet, steady operation at night is more important than maximum cooling power.

How the two air conditioners work together

The rear Dometic FreshWell and the front SINCLAIR ASV-35BIS now work as two independent zones — each one only cools the part of the vehicle where it actually is. Instead of one unit trying to blow cool air through the entire interior, I have two smaller units that cover exactly their own space and don't need to expend as much energy doing it.

Energy-wise, it even handles operation away from a standard mains connection. Thanks to the LiFePO₄ battery bank and the Victron MultiPlus-II, it's possible to run both air conditioners at the same time along with other appliances without worrying about a fuse blowing or running out of power — the system handles it without problems in normal operation.