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I think you mentioned something like $1600/annum--that's less than $150/mo. Normally insurance carriers will provide billing on annual, semi-annual, quarterly, or even monthly intervals. It might cost a small premium, but probably not more than 10% max.
If you can't come up w/ $150 in a couple of months, you're not charging enough or not working enough, or both. You certainly should be able to find plenty of A/C work for individual homeowners at this time of year with nothing more than seasonal inspections/startup woes, etc., to not even need referrals. If you're that strapped, my suggestion would be to go back to work for one of the established contractors for six months to a year and work during that time to build up some cash reserves.
Best advice I have, unfortunately. Good luck...