My 1996 E320 was recently in the shop for a self-inflicted radiator replacement. Don't ask!

Anyway, after I got it out of the shop The climate control works as it originally did should sending nice cold air to the pasenger vents - but considerably warmer air (20 +deg) to the driver side. The shop mech says the two are not related. (meaningful discussion with him later). The cool air will flow to the driver vents after about 15-20 min of operation. Q- Next step, diagnosis from local dealer? But meanwhile what is the obvious diagnosis? if it is obvious?

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Regards, JonasJackson