Coolant temperature too high

[kramlavud]

A trusted Indy replaced both auxiliary electric cooling fans last week. Now while waiting at a traffic light with the A/C on and 95 F outside temp, the gauge rises quickly to about 120 C, the auxiliary fans are on, and the A/C blows warm air. Once moving the temp falls to about 90 C, and the A/C produces cold air. This is a '94 E320 with 145,000 miles, with possibly the original radiator.
What's happening?
Mark