Hey doc- an RN from Chicago consulting with you here! Our 190d had similar symptoms where sitting in traffic idling for long periods, and driving up steep inclines at highway speed would cause the temp to climb relatively high on the guage. After chasing several possible causes- I ran her till she got hot, and saw that the fan would not engage. I used a jumper wire to activate the magnetic fan clutch (which clicked beautifully), so the switch that activated the clutch turned out to be the first problem. I replaced it for $40 US. After the AC was repaired she began to overheat again- this time it was a disconnected wire to the pusher fan similar to the one you have described. With these two problems addressed she rarely runs hot- even at highway speed, with 4 passengers, climbing a hill with the ac on. I think you may have found your problem in the switch- with the new cap and flush you've done good preventative maintainence as well. Good luck- John