I replaced the MONO valve for $40.00 and the heat works perfect. If any one would like details of how I did it. Please feel free to email me.
1988 560SEL, Green, Chrome wheels.
2000 Suburban, 20" wheels, DVD, wood grain dash (wife's car).
67 Beetle euro, Lots of Empi parts.
69 Beetle conv, 1980s cal look.