Hi,
My 99 E300's driver side blower blows warm air after about 30-40 mins of driving. The remaining center and passgenger side blowers continue to blow cold air.

Can anyone pls advice on what may be causing this warm air blower issue...?

Note: just above the rear view mirror, these is a cavity, some electrical sensor (i guess) fell off. Not sure what this cavity is for and if this is causing the warm air blower issue.
Thanks.