Manual switch is a bad idea, unless it is simply to disable the compress. (though, why you would want to is beyond me.) Question becomes, SHOULD the compressor by shutting itself off occasionally? Do the pressures indicate the compressor should NOT be running?? Under good conditions, the compressor WILL run constantly..... and that is perfectly acceptable. Put some gauges on it, see what pressures are, and go from there.

Could also try unplugging either of the limit switches, and see if the compressor kicks off.

 

I don't see how a manual switch would hurt if all it does is cut power to the clutch. Weather is starting to get cooler too. You should soon be able to leave it unplugged till you get it fixed.