I am not a newbie mechanic, when it comes to working on older trucks, but I don't know what is involved with replacing a heater core on my '89 W250. I know the one in my '01 was pretty involved, with draining the AC and all, I actually took that one to the shop. That being the only thing I have ever taken to the shop to get fixed, does anyone know how rough it is to swap one in an '89?

 

Here ya go.
How To Remove The HVAC Box - Dodge Diesel - Diesel Truck Resource Forums