Solving Heater Problems on the Mercedes 300D, W123, With a Klima Design Works Kit

A common reason for lack of cabin heat on the 300D is a bad Monovalve that doesn't open or shut properly. Rebuild kits for this valve are poorly made and rarely last very long. I ordered a Monovalve & Circulator Pump Elimination Kit from Klima Design Works and it solved my problem easily and works well. This is an independent look at the kit. I am not affiliated with Klima in any way and I bought my own kit. I did have a couple of questions before installing the kit and Klima was great about answering all of them. https://klimakit.com/