Hi Redman,
I'm on Playa Golf 2 and had A/C pre-installation from San Jose. Yes they do build the plumbing and electrics into the walls so in theory, all the installer has to do is connect up their units - no drilling needed. IN THEORY !!!!
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In practice, every installer I phoned for a price said that there was no reduction in cost for pre-installation because in many cases the pipes are kinked or broken by the builder and it causes them big problems. They would much rather start from scratch and just drill through the walls to install. The advantage I saw with pre-installation is that there is no trunking on the inside walls. If there is no pre-installation then the installers will just run trunking (to conceal the pipes & cables) from their entry point to wherever you want the internal unit fixed and this can look unsightly.
My installer (Gary Leggett - 0034 678008831) did have a couple of problems and ended up having to dig into the external wall to repair one of the broken gas pipes. I must say, he was very helpful even though it was really San Jose's problem to fix since they did the pre-installation.
I think you just have to judge if you want to live with trunking along the inside walls or not. If you can live with the trunking you can save yourself about 300 e per room by forgetting about San Jose's pre-installion. If (like me) you prefer to have no trunking visible on the walls, then pre-installation is the way to go, but just be aware of the possible problems.
Incidentally, I don't think that A/C units come with any pipes or cables - the installer supplies these (usually at a cost) unless of course you have pre-installation.
cheers & good luck !!
Tom