I had a problem with a newer truck and the relays burning out for the air conditioner. The relays got so hot I couldn't touch it. After having a "professional" diagnose the problem as the blower motor, thermostat, switch and charge me $500, after several failures, I finally figured out the the charging system was failing and putting out too much voltage. I switched out my alternator and the problem was solved. Might want to see what kind of voltage your system is putting into your battery under load.
