The M.B. 1990 190e 2.6 heater is on the right front near the side not far from the firewall. BUY M.B. as the car puts out so much heat it melted the plastic tube that inserts into the feed and the pressure of the clamp caused it to collapse and ultimately leak within a few weeks!

I still have my old climate control that works most of the time, but sometimes gets goofy if you need something to test with.

Check for vacumn, without it the heater valve will stay open and bake you in the car. Then check to make sure that the valve mechanically operates to close. You can alos tell by putting you hand on both sides of the hot water feed hoses. One side will be HOT, the other cold or at least only warm if closed.

Good Luck,
George