Hello Jeff, This is from toyotaownersclub.comforums
I have the same problem with my 97 model, having replaeced the pressure switch, checked out the electrics with Auto electrician, the only remaining item to test/replace is the Air Con amplifier which is costly around £120.00 so am seeking out a re-claimed unit. The Amp is located behind the passenger glove box fixed to the inner wing. hope this helps.