Volks,
Having dealt with the dilemma of trying to cool the air in my 82 diesel
Westy for some years now in Baja Calif, I've come up with this:
I use a Toyotomi 4000btu portable air-conditioner inside the van. It's the
most efficient, small A/C unit I've found.
That coupled with a Honda EX 650 mounted outside on either the front or
rear bumper. It uses .5gal of gas every 4 hrs. Is so quiet no one notices
it's on. 

With this setup, my 1.6L diesel isn't over taxed ( more overtaxed, I should
say) and I've got air whenever I need it.

Works for me.
Bob Bellanca
`81 Diesel Rabbit
`82 Diesel Westy (soon to be 1.9L turbo, I hope)
`84 Turbo Diesel Jetta