Max AC Clicking/Tach Problem

New guy, first post. :)

These may be two separate problems, but they sure do seem to happen at the same time.

One day, I was minding my own business with the A/C set on Max when all of a sudden there as a constant annoying click coming from under the passenger side dash. It stops if I turn it to normal A/C, but it's July in TX right now and that just isn't quite enough on some days.

Sometimes I can turn it to Max and it will work OK for a few minutes, but then the clicking starts up.

At roughly the same time, I noticed that my tach would run really low and it seems to be only happening if I go to Max A/C. It will read below the zero at idle, and seems to be about 1k or so less on the highway. If I switch back to normal A/C the tach problem will not go away unless I stop and turn the car off and back on. It has also happened twice with my speedo, but that might be question number three. . . .

Any ideas?

Thanks in advance!

Could possibly be a ground problem, that's really all I can think of. Find a wiring diagram and see where the grounds for the IPC and A/C relay are, they could share a ground and having the A/C on is enough to cause a volt drop in the ground.