Denso designed & built that system to a PRICE...no heater valve..has a control unit (amplifier) that evaluates the in-car temp & position of the temp wheel & opens or closes (in stages) the blend air door...seems to work good for a basic system..went to A/C/C in 2002 with dual controls.

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MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator