MKII 1991 jetta heater core box rebuild I didn't have any heat this winter, and I thought I needed a new heater core. MKII Jetta heater cores are known to go bad. Another problem I had was foam blowing thru the vents and hitting me in the face and spreading out all in the interior. So this weekend I went to replace the heater core, well I tested it , by cutting an end of my garden hose off and splicing it into my heater core circuit and connected it to the hose. I turned the water on, my hose spigot at the house is tied in before the regulator so it is like a firehouse. It flowed perfect and I had a lot of water pressure on it ...so in turn it was fine, and no gunk came out , so hmmmmm what's that foam blowing out deal about? EUREKA! I opened up the bottom of dash, there is a cover that is hard to get out, but by being forceful it will come out! When I did finally get it to opened up this is what I saw, you can see the foam is gone! The "holes" in the door lets the cold air come in no matter how much you have the heat turned up! I replaced the foam with some "foamies" it is self-adhesive foam from the craft dept at Wal-Mart, it's 50 cents a sheet and it very sticky. So sticky in fact I will start to use it to outfit my kayaks, water does not bother it.  Here is what you get to see...  I held one door open so I could get the other door that was deeper inside the fresh air box The picture where I have my fingered pointed will open the first flap so you can get to the one in the back   Here is what it looks when installed, With this last picture you can see what parts of the dash I had to take out to get my hands on the cover that was covering up the fresh air-heater core flap doors This job took about 3 1/2 hours but now my A/C blows cold and my heater blows hot with no foam blowing in my eyes and the problem is solved without a paying a mechanic who might have had a hard time figuring this one out .