Hello all, I'm hoping you can help me solve my heat (or lack thereof) problem. I bought my 1985 300D last June w/o working A/C. My brother and I were finally able to get everything up and running and now I have little to no heat. When we first got the A/C running I could switch between blowing cold A/C and hot blowing heat, but now I get lukewarm air at best. If I start the car with the heat on it blows hot for a bit, but as soon as I start driving it cools down. In getting the A/C up and running we repaired the monovalve with a repair kit and I checked it today to make sure it was still in perfect condition. The car runs at just over 80 degrees celsius, rarely much hotter or cooler once it's been up and running. It doesn't take an abnormal amount of time to get up to 80 either. My brother and I are pretty stumped at this point and I'm hoping someone here can help.

Car Info:
1985 300D Turbodiesel
Electronic/Auto Climate Control