I tore my console out to test the check valves for a leak "before" I recalled that the most common leaks often take place in the vacuum bundle that runs alongside the battery. Battery acid will get inside the bundle and eat the plastic vacuum lines. Mine had several that were eaten by acid and I had erratic climate control problems. I spliced them and now everything works fine.
You do need a Mity Vac to troubleshoot this system along a vacuum guage and some golf tees to plug lines as you troubleshoot.
It took awhile but I also found my defective trunk actuator.
It is time consuming but worth it to me after paying $400 to have an independent fix vacuum leaks.



1980 300D