Interior climate sensor

1989 300E. I have been having climate problems where there is only heat in the car and no cold. I was told that the interior climate sensor at the dome light could be dirty. I looked at it with a flash light and noticed that it looks like it it clogged with alot of dust. How would I clean this sensor and or test it to see if it works. Also how would I remove it from the ceiling of the car?

Thanks

Fab