1999 Subaru Impreza Outback - AC

My AC problems are stumping my mechanic. The AC works intermittantly although pretty much on the not working part of intermittent. My mechanic’s confirmed there are no leaks, that the compresser works and the AC relay is okay. The thermal protector switch (?) needs replacing but he was able to kick off the AC by bypassing this and running direct power from the battery. Bottom line is that the AC works when powered directly from the battery (through the AC relay) but it’s not getting the power signal from the system. He seems to think it might be a problem with the computer or ground wire somewhere. Any ideas?

I’ve a buddy that insists upon calling his Subaru “the microwave” because the a/c doesn’t work well. (We’re in Alabama.) I’ve never had a problem with mine - until I borrowed another buddy’s Toyota Corolla its a/c gets up to speed (down to business) faster and colder than mine ever has.