Lately I've been having an issue about getting heat while the car is at any sort of speed. The heat works perfect at idle in the driveway, but when I increase the rpm's to anything over 1800, the heat gradually fades away to cool air. Sometimes the heat will return when at idle....sometimes not. I believe the ACC is working correctly as it cycles the vents and changes the temperature of air properly while at idle. The aux pump is also working correctly at idle ( I can feel it running with no vibration....nice steady hum.)

In checking the monovalve, I can hear and feel it clicking with selector in full cold. Conversely there is no audible click with full hot selected, although there is a very, very slight electrical vibration (barely detectable).

This spring, I had an issue with the monovalve. I was getting full hot all of the time. The rubber diaphragm was ripped. A repair kit solved that problem, but I did notice that there was some corrosion inside of the valve itself. I am wondering if this corrosion could be the cause of my current issues.

Any suggestions would be appreciated.

Jon

'85 300D 97k