Hi folks - the climate control in my '80 300SD works well for the most part - plenty of heat, especially in Vancouver Island's relatively balmy winter weather. But every now and then (even when the in-car temp is still relatively cool), it blows a blast of frigid air for 1-3 minutes before once again kicking out the heat. Is this normal? If not, what's a likely reason for this?

Cheers.

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1980 300SD (The Green Machine!)
180D Ponton (paid $100 Cdn - sold $200!)