Former VWDieselParts.com Forum

I dove into the deep end and am replacing the heater core on my Diesel Jetta. 1991, normally aspirated, non-a/c. Really not that bad and I am not removing the whole dash!! I really appreciate the simplicity of the early models.
The original foam gasket, wherever it may be used, is pretty much rotted....not all of it has to be replaced though, as I don't mind a little leakage here and there.
I noticed, as in the photos, that the door in the heater box that moves when the dash temperature control knob slides has had some of its holes partially covered.
Half of the holes in the 10-hole door panel (2 small and 3 large diameter) along its length and half of each hole in the 7-hole door panel. Some of the old foam was still there. See photos.
Some German guy on Youtube puts solid foam panels over all of the doors.

Question: What is the deal with the foam over the holes...yes, obviously to block some of the flow.
Do they block other holes for different operating environments?? 3m makes some high temp foil tape that is good to 600 degrees F.
Has anyone thought about this???? Comments, please.

All of the holes get covered.
I think the holes just make the metal lighter.

Agreed. Metal tape over the whole thing. It'll be Winter again soon enough, and you'll be glad you did because these little diesels don't make a whole lot of excess heat.

Yep, holes make the flaps lighter.

Tape is fine... Done it to a few cars.

But I will say that my '86 flaps rattle badly, so there is merit to using something to dampen or support them.

I believe that the holes were to make the flapper door lighter as well. Cover all the holes.

I used some HVAC duct tape. No, this is not your cheap hardware store duct tape. I had to get it from an HVAC supply store and it's got a silicone backing that will literally stuck to just about anything it touches. Once it's on, it's there to stay.

82vdub's picture shows what I call the 3-hole diverter door. It routes the airflow either up or down in the duct work and can, along with the plastic defroster door, route all airflow to the defroster ducts. So, basically it directs the airflow. That's what it does in my 1991 Jetta heater box. Covering it completely would seem to be ok.

In my pictures you see the temperature control 10-hole/7-hole door. My foam was almost completely gone, so I'm just going on what I observed before I cleaned it up. The 7-hole and 10-hole sides appeared to only have part of the holes covered. I am thinking that some air should always flow over the core to prevent it from getting too hot in there when the heat is not required. Albeit, even with all holes covered, some air will slip by the doors and over the core.

Has anyone any thoughts on this? Or am I being too nit-picky??

i.e, Is it the consensus that all of the holes in both doors be covered??

Yea, you're being too picky. If you leave a way for the air to flow around a flapper door (or through a hole in the door), that's what it will do. You will end up with marginal heated air in the winter, and overly heated air in the summer. Cover all the holes in the doors.

It sure looks that way. Consider this: What happens when the car sits idling with the blower off? The heater core sits in still air. It and its surrounding components are made to withstand the heat.

I like Tyler's idea about soft bumpers on the deflector edges to reduce rattling. Band-Aids would be perfect.

IIRC, the stock foam extended past the edges of the metal flaps to seal the chambers and suppress rattles.

And yes, if any holes are open, you will regret it in both summer and winter... cowl air in summer is already too hot, and unless the core is like new, it can have issues making the vents hot in winter, without adding cold to the mix.

TylerDuren,

I've taken the consensus opinion and sealed all of the holes with high temp, foil-type tape. The heater box is already back in my 91 jetta. If the doors rattle bothers me I will pull the unit and put some foam in there. Interesting that almost all of the foam was rotted out and the heater/defroster seemed to work ok. It should now be much improved.

I had little problem pulling the entire blower/heater box unit out of the car, so I don't fear having to do it again, especially that now everything is nice and clean and I know what I am in for.
The worst part, i.e., most difficult, was putting the central air ducting that flows air to the upper windscreen and out to the interior. Patience was the key for me !!!!!

I appreciate everyone's help and encouragement. This forum is fantastic!!! Thanks to all of you.

Thomas

Well it appears you have a fair amount of mechanical ability,.. if that was concidered easy.
Most of us pull the front cover while keeping the dash together.

I know this refers to an old post, but I thought you might have the requisite information regarding my need.
I've just installed a new heater core in a '97 petrol Golf. The heater core is hot at all times, since there is no inlet valve.
Now, the heat's not working very well - even though I've gotten all of the air out of the core and the core outlet hose is nearly as hot as the inlet hose. The defroster isn't working at all well.
When I did the work, I found that most of the material that was covering the air routing flaps was rotten. So I removed it and covered it with some other material. I'm thinking that this material has come lose and is preventing the air from blowing past the core. Since I surely don't want to remove everything that I did, in order to replace the core, I'm thinking about just cutting my way in from the outside and glueing it back together when I'm done. Do you think this might work OK? - Michael, Oregon, USA

There's a couple flapper doors inside the heater box. One directs air through or around the heater core (coolant flow goes through heater core all the time - air temp depends on flapper door position), and there is a deflector to direct air to the floor or up through the vents. I did my heater door repair two winters ago and it worked great as can be seen from the picture above. I didn't use plane jane duct tape, but I used a super industrial silicone type aluminum backed duct tape that professional HVAC system installer use to seal up house ductwork. It sticks well, and sticks to dang near everything and anything. Duct tape falls apart after only a short time. I would suspect that your repair has come undone over the years and that you need to do it over again. I don't know about the access for a 1997 vehicle, but for my 86, I accessed it through the large box under the dash in the center of the car. I removed that and the flapper doors were accessible fairly easy from there.

I'll give it a whirl, though I'm afraid that I may need to cut my way into the heater box from the front. I see that someone else has used muffler tape to repair the air flaps, which I do have and I think it similar to the product that you used. Thanx for your time and help with this issue.

I don't think the muffler tape and HVAC tape is the same thing. I'm thinking too large of a temperature difference to be the same product. I looked on the roll of HVAC tape that I have, and there's no manufacturer name on the inside of the roll. I don't think it had anything on it when I got it two years ago. I know that you can't walk into any store and buy the product (at least around here), you have to have an account with a wholesaler of HVAC products.