VW Golf Mk2 Owners Club

worry not, this is common on every old banger... its the aging of seals and foam on divertor on heater matrix/cabin fan box. theres a how to somewhere on forum, clean as much old foam off from divertors, and vent flaps, replace with closed cell stuff and or foil hvac tape.. you'll notice improvement in winter when warm air demists windscreen.


https://www.vwgolfmk2.co.uk/clubforum/index.php?topic=64.0

I'm sure someone can recommend better foam than I but this is what I have done.
You want to stop any air getting through the flaps. When you dismantle the heater box you will see why. A small amount of air will get past the flaps anyway. Removing the old membrane of glue is awful. Use some adhesive remover.
I used sticky A4 foam sheets from Hobbycraft. They are cheap and readily available. However you will need to cover it with sticky aluminium tape (insulation tape) because the stickyness will degrade over time. I found that out when I took my heater box out to install aircon. I'd recommend you completely cover the foam with a good overlap of Ali tape. This time round I have put a lip of foam round the edge of the flaps so they don't rattle and covered the whole flap with Ali tape. Put the box back together and test the flaps have full movement before refitting.
If you take the full unit including dash and pipes you probably want to clean then out of all the little bits of foam.
When done there is the foam round the actual vents that you may wish to renew. Not done that yet...just removed it!
If you do take the dash out. Check the leading edge is sealed (demisting will be cr4p) and the heater aperture is the correct shape (reshape and reinforce with sheet plastic and coat with a PVA solution to restore rigidity)
Good luck!