I have 2002 Mercury Villager. Have Mysterious Overheating Problem!!!

What is your question?

We have exhausted our thoughts on what can be making my van overheat. We replaced the fan motor, replaced thermostat, reseated distributor, had it timed, had new fan relay put in and it blew and replaced again, changed oil and its fine, no milky colored oil. Changed belts for a/c and steering pump, new steering pump, new water pump. Still overheats when sitting at red lights or when a/c is on! A/C blows cold sometimes and warm sometimes. My son in law suggested the a/c clutch may be going out. We are stumped!!