Type 4 Heater Elbow - how does it work?

This is (hopefully) a really noddy question. I have tried to Google it, but it's one of those that is probably really quick to just ask someone knowledgable.

I have a type 4 engine, and am slowly sorting my heating.

Does the heater Elbow Valve vent to the outside when it is closed? If so, how? it only seems to have one one outlet (outlet to the cabin only).

Or, if it does not vent to outside, where does the heated air go when it's closed?

Thanks in advance.

 

This explains all

http://myweb.tiscali.co.uk/freemefromthishell/vw/T2 Heating.htm

 

Thanks. Yes, I've read that. The bit that confuses me right now is how air escapes the heater elbow, as there is only one outlet. The old porsche system had the same setup, but there was two outlets in the elbow, one went to cabin and one to vent hot air straight under the car.

 

Heat should come out the mushroom on top of the elbow.

 

Ah ha! Didn't realise that was an outlet. That explains that then. Ta.