Air Conditioning Relay problem?

Hello-
I'm new here. I've got a '94 wagon. The ac has never worked & i never bothered with it. but after a little nagging from the ol' lady, i looked into the problem. turns out the compressor isn't activating. I traced the problem to the relay mounted on the firewall. A little tap on top of that relay & the compressor fired up & she blew ice cold air. So i went to a junkyard & paid $2 dollars instead of paying ford $37 for a new relay. Surprisingly, i still had the same prolem. So i went & got another, just in case this was a common problem with those relays. Once again, same problem. I'm stumped & i'm hoping someone can give me some advice. otherwise, it's off to the dealer to get the wife a new car!! I'd really appreciate hearing from some folks that who may know what's going on here.
Thanks-
Mike

Since you have had three different relays I was thinking maybe that's not the problem after all. Could have just been a fluke that it started up when it did. Try by-passing the switch on the accumulater-dryer. I'm thinking this switch is bad or there is not enought refridgerant.