Mercedes: Heating, thermo vacuum, vacuum valve

Question
Can you please tell me what does the heater valve and the thermo vacuum valve does.I own a 93 190e 2.3 mercedes. My blower works fine but there is very little heat.

Answer
No heat = low coolant, no vacuum signal to heater valve or bad heated valve.

Thermo-Vacuum Valve is a two position valve = open/closed, installed in the engine water jacket, when it reaches temperature the valve opens passing vacuum.
http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=merc...

The heater valve is a mechanical valve with a vacuum motor attached to control operation.  
http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=merc...