Mercedes Benz repair: Heating system, mercedes benz 190e, mb 190e

Question
I have a 1991 MB 190E (2.3 L).The Defogger duct is always blowing hot air without any selection. What could be the reason?

Answer
Answer:
Possible bad heater valve or loss of vacuum to valve.

PART NUMBER SEARCH RESULTS WITH PRICES
Vehicle 1991 Mercedes Benz 190E 2.3
Part: Heater Valve
 Note:  Vacuum controlled.
R3020-11893 Heater Valve Germany IN STOCK $20.58  
 
R3020-11893 Heater Valve IN STOCK $20.5

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