Shalom!

My problem is every time I start my tsikot (Space wagon with carb engine), it idles at 400rpm then it goes up to 800rpm when the engine is already hot. And when I turn on my a/c it idles back to 400rpm (engine vibrates horribly, gas pedal seems to be hard). But when the A/c compressor goes off, it idles normally at 800rpm. What seems to be the problem? Recommended shops near pasig/ortigas area please. Thanks!