The A/C should only come on with the windshield defroster, if it comes on at all. My Cavalier is designed to do that. This does two things, 1) it prevents the seals in the A/C system from drying out, and 2) it prevents problems with overheating the windshield by pulling moisture that builds up inside of the car and providing more even heating.

I don't believe the 1997 Dodge trucks are designed for the A/C to come on with the heat or the defroster.

 

When I was in Alaska had a newbe try to run straight antifreeze. He called me up said his truck was froze. I went over and poped the cap it looked like a lime snowconein there. I told him you got to have water to activate the stuff. Towed him to the craft shop on post drained out about half and put in some water. While we were at it put in syn gear oil.

 

I would expect all 2nd gen rams will use the a/c to help with the defroster... my '93 jeep GC did with the 318, as well as my 2000 ram...

 

My A/C works on defrost. 18 deg here this morn and the heat will run ya out.

 

The A/C turns on with the defrosterbecause it dries the air out. Remember in the summer when there is a pool of water under your vehicle when you are running the air conditioning? The moisture is removed from the air when run through the evaporator unit. Assuming you have your heat turned up, the air is then heated back up by the heater core. This warm, dry air is much more effective at removing the moisture (fog) from you windshield.