My suggestion would be to check the engine coolant thermostat for proper operation. Even though your wife's car does not have automatic climate control, it might still have an interlock between the engine temperature and the blower motor.

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Robert Fini

'12 ML350 BlueTec, 100k
'06 E320CDI (x2)
'05 T1N Sprinter 2500/Pleasure-Way Plateau TS, 70k
'97 C36AMG, 319k (son's)
'94 E320T, 249k
'93 190E Sportline LE, 168k (daughter's)
'84 190E-2.3/5spd (Stage Rally Racer)
'66 230 W110 Sedan (Barn Find, Vintage Racer build in progress)