The water cotrol valve (to control the heater) is between firewalls located under the hood. This is the same place that holds the wiper motor.You remove the plastic cover to access this area. To acces the vacuum for the defrost vents you need to remove the instruments. This vacuum unit is a small rectangle about 2X3X4. To remove the instruments first remove the left hand vent. Pull out the pannel 1 to 2". With a small hand reach into the vent and disconnect the speedo cable. There are 2 more vacuum elements behind the radio and center section. Any vacuum leak will give all heat in defrost.

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2009 CLS550 55,000
2004 ML350 144,000
2004 X5 95,000
2002 X5 165,000
1996 320S 155,000 (sold)
1991 190E 192,000 (sold)
1989 300SE 160,00 (sold)
1984 300D 210,000 owned since 85, (sold)
1984 300SD 160,000 (sold)