Why does fan blower motor for AC and Heat work part of the time? on 1999 Mercedes-Benz C230

In particularly hot or cold conditions, the fan seems comes on after the vehicle has been running for a while. Maybe five or so minutes. Sometimes it does not come on at all. Also, when driving on interstate on hot days, it turns on and off for no apparent reason.

Asked by for the 1999 Mercedes-Benz C230