My seats don't heat as they should. The driver's seat heats on Stage 1 but not Stage 2. The passenger seat doesn't heat at all. It kinda worked better last year, but not without problems. I checked the auxiliary fuse. It looks good. The indicator lights on the switch work properly. Where should I look for the problem?

Where is the heater control unit located? The cd manual does a poor job of showing the location.

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95 E320 Cabriolet, 169K