No heat help.

[Tac]

Hi every one, ever since I replaced the heater core in my 1991 Jetta N/A I have no heat. It's such a pain to take it apart I was hopping maybe to get a idea whats wrong. It does have AC but I took out the hoses for it and left the rest in side. I do fell cold air coming in on the Passenger side. When I put my hand under the dash you can feel it pretty good. Also the vent on the inside doesn't have any more of that grey foam or insulation on it. It's just the vent with the holes in it. I hope some one can help It's starting to get cold here, and I'm Freezing on the way to work. It use to work really good.

Thanks
Tom

[82vdub]

Did the flapper doors inside the heater box have foam on those doors? When you turn the blower fan up high, do you get air coming out of the vents, and if so, does it seem to come out all the vents (defrost, dash and floor) at the same time? If you have the last symptoms, your flapper doors don't have foam on them anymore, so air will flow around the heater core, and out any of the vents in the car. If you're not getting much air flow through the vents, do you get more or less air flow when the heater lever is towards cold than when it's put on hot? If so, maybe there's some leaves blocking the heater core and you can't get air through the core.

[TylerDurden]

OH MAN.... you changed the heater core and didn't cover the blend-doors? You have permission to kick yourself in the rear!

The core is constantly hot, and one door with the holes (in the back) directs the air through or around the core to "blend" the air to temperature you like.

The door in the front diverts the air to the dash or to the heat/defrost ducting.

I'd pull the console (if present), the knee rail (if present), pull out the center dash vents and the duct in the front to the dash vents... that will get you into the front of the airbox, where it is possible to cover the blend doors with aluminum tape.

The front opening is small, so delicate hands or clever tool use is a plus, to get tape over the front and back blend door.

Google "vw mk2 heater blend doors" image search and peruse the trove of pix like these:





Blue= cold air
Red = hot air
Purple = blended air
Yellow = door movement & core

The door closer to the firewall directs air to and/or around the core for temperature adjustment.

The door near the front directs the blended air the the vents or to the flapper on the left.

The flapper on the left directs up to glass or down to feet.

[Tac]

That's probably it. I did just the opposite I cleaned off the rest of the foam when I changed the heater core. The pieces of foam were blowing through the vents. Luckily I never put in the console or the knee bar suspecting I was going to have to take it apart again. Thanks for the tip about not taking the whole thing apart. This stuff has been apart for quite a while.

Thanks
Tom

[82vdub]

The top two pics are from my install. The silver tape that I used is special HVAC aluminum backed tape, which is not the stuff you buy in a regular store, or plane duct tape. The layer of silicone on the back is thicker than the plane aluminum backed stuff found in stores, and is extremely sticky. First time you use it you'll destroy the piece you tear off the roll to use as you can't get it unstuck from your fingers, or whatever it first touches. It's a fairly easy job to do, it just takes a little time to get to the flapper doors.

[Tac]

I have the aluminum tape that has the peel off back that has another kind of coating on it for taping the aluminum insulation to wrap around duck-work. I also have some of the tape you use for putting in new construction windows. That's aluminum with a peel off back. That stuff is really sticky and evil.

Tom