I guess you are talking about the heater underneath the rear bench.

Yes, it is a bleeder valve . Not all rear heaters had this bleeder valve.

Next time you bleed the cooling system, you have to open three bleeding
valves.

Hans Brouwer
86 Westfalia
92 Cabriolet

Robie Pierce wrote:

> What is white wing valve do on heater box? A system bleeder? How do you
> work it?
>
> Cut off bottom of covering box by whacking hard on stiff putty knife on
> both sides.