whine from dash related to heater controls 1985 280 sl

[oldan]

Whine occurs only after car has run at least 15 minutes

Whine happens only when heater is on off or economy or normal

Whine stops if bilevel or defrost buttons are pushed

Car does need a refrigerant recharge

The sound may be coming from the key buzzer but it is a much higher pitch and
not as loud as the key buzzer.

Any thoughts on what causeds the whine?

Thanks

[oldan]

Whine happens only when letting up on the gas. Never occurs while car is in normal forward motion.