Try the simplest thing first. Take a 2" square thin tissue paper, and while the blower is on high, cover the intake grill of the cabin temperature sensor. The tissue should stay put. If it falls down then, using a vacuum cleaner, clean the inlet grill and try the tissue test again. The intake grill is about 1" square and is located in the overhead console.

That's an easy, and quick test to try before you go on to more complicated diagnostics.

Phil

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'95 E300 Diesel, 264,000 Miles. [Sold it]