HVAC in the key of Volkswagen – heater core and HVAC foam

Having run out of time the other major car working day with Tom, I wanted to dive in and finish the winter prep for my car by making the old and ailing heating and defrosting better than new with two major projects.  As with so many things in life, you have to fix one thing in order to fix another, as per Hank’s Law:

Hank's Law: figure on being forced to fix at least one secondary problem, in order to be able to fix your primary problem

Hank’s Law: figure on being forced to fix at least one secondary problem, in order to be able to fix your primary problem

Without further ado, my Friday and Saturday afternoon and evening… and Sunday morning… (and a few hours here and there over the weeks which followed) were spent on:

Dashboard removal.

I had to set up a small work table of sorts for the laptop and Bentley manual, and tools

I had to set up a small work table of sorts for the laptop and Bentley manual, and tools.  Also 500 watt floodlight for too much light and a little needed warmth (it was 45 outside)

I couldn’t do any of the other three projects (the third being installing soundproofing behind the dash while it is out) before doing this, and as the TDIClub forums attest, this is a real pisser of a job.

As a general sense of how the garage looked as I disassembled the car to its barest bones:

Now to try and put it back together...

Now to try and put it back together…

Not a lot of fun to keep track of parts, and thus I relied heavily upon masking tape labels (particularly for wiring harnesses) and Sharpie’d bags with different types of screws and clips removed:

labels galore, and I still have some fears I didn't label enough!

labels galore, and I still have some fears I didn’t label enough!

A thousand different screws, bolts, and electrical connections to not only remove without breaking; you also have to remember how to reassemble the damned thing AND do so in such a way as to not cause rattling of something loose.

HVAC foam

A known issue on VWs around the age of my car (and likely, more cars besides), is that the foam used as gaskets on the mode and blend doors (which mix air from the outside with air from the engine for heat or from the AC for cold) will rot and shoot out of the vents – this happened to me in February 2014, en route to Maine for winter camping.  The air temps coming out of the vents plummeted, and that is no good – no more real defrosting capability as a result, which is a serious safety issue.

So on grounds of not being able to safely drive in the winter and also wanting to continue to learn as much as I can about the car and making sure it will last for many years to come, I dove in!

The dash fully removed, but stuck on some of the wiring harness...

The dash fully removed, but stuck on some of the wiring harness…

The actual process for dash removal was significantly less stressful because I had previously taken out the interior of the car to prep for the welding project which needed doing – so I “only” had to take the dashboard out.  What a pain in the arse.

First view of the blend and mode door.   They ought to be 100% covered with a grey foam gasket; they are completely bare because it rotted away (and blew out the vents into my face!)

First view of the blend and mode doors (the metal with the circular holes). They ought to be 100% covered with a grey foam gasket; they are completely bare because it rotted away (and blew out the vents into my face!)

Using the high temperature-rated adhesive foam from McMaster Carr atop some extreme duty HVAC aluminum tape, the various doors and shunts were cleaned of old foam/mess and given their new coats of armor.

Heat box disassembled and rebuilt, note the new high temperature adhesive foam from McMaster on the internal doors

Heat box disassembled and rebuilt, note the new high temperature adhesive foam from McMaster on the internal doors

But that was nothing compared to…

The goddamned heater core

The biggest and last project for these three major winter repair and/or improvement projects on the car is the heater core – the component which uses hot engine coolant and draws air through it to transfer heat into the HVAC system.  While mine was not (to my knowledge) broken, when they do break they leak coolant into the HVAC system, and its a pain in the ass to take the dashboard out.  So, since I am having to do that anyways to do the foam, I went ahead and decided to do some preventative maintenance here by replacing it.

Finally yanking the stock heater core!

Finally yanking the stock heater core!

That said, thanks to the wonderful people at the TDI Club forums, specifically this thread (which my good friend Mark recalled and was able to find for me when my Internet’ing skills failed me)… I will be upgrading this part as I replace it.  The stock design uses plastic components internally somehow, but most egregiously… the piping to and from the engine coolant lines is plastic and apparently consistently breaks at a certain bend.  Thankfully, as per the thread above, one model newer than mine (I have a Passat B4, so we’re talking the Passat B5) has an all-aluminum and generally heavier duty heater core.  It is a tight fit but it will slot into place; the metal coolant tubes are at a different angle than mine so will require slight modification… but I can do this job once and right, so I won’t ever have to do it again (crosses fingers).

New Behr core on the left; old Valeo on the right

New Behr core on the left; old Valeo on the right.  Note the wider spacing on the heat sink patterns on the Behr; I suspect this will make the heat even meltier than it was before!

Having done the process now, I can honestly say that the worst part was removing the ductwork from behind each vent on the front console and dashboard – after some 20 years of hot air and cold air coursing through them, the plastic didn’t really want to move at first.  As this excellent guide for the Passat B3 (fairly interchangeable with the B4) puts it: “No really easy way to do it, but I wiggled and pried and cursed till all the vents came out.”  I too used the wiggle/pry/curse method, and a helping hand from my dad, and got the damned thing apart.

The heater core is such a simple part - pulling in hot engine coolant through one tube; using the heat sinks to heat the air around it within the heater box, then pushing the coolant back into the engine.  It is just *buried* beneath the dash and a million pieces, and takes forever to access!

The heater core is such a simple part – pulling in hot engine coolant through one tube; using the heat sinks to heat the air around it within the heater box, then pushing the coolant back into the engine. It is just *buried* beneath the dash and a million pieces, and takes forever to access!

It was a 3 hour long period of fighting with it, but I found out via hard-earned wisdom that I cannot reuse the old coolant flange (molded plastic piece to ensure that the tubes go through the firewall into the engine but no exhaust or oil can get into the car cabin).

Shaping and bending the aluminum shim to provide a relatively solid core to the new flange

Shaping and bending the aluminum shim to provide a relatively solid core to the new flange

I was forced to buy some aluminum and fabricate a multi-layered “flange” of my own, putting more of that McMaster foam atop the aluminum core, and then using a combination of high-temperature RTV gasket making sealant and finally aluminum extreme weather HVAC tape, to have a good seal on the firewall:

Final product.  The foil weather tape appears to stick best of all to aluminum - the firewall's covering is aluminum so I have high hopes that this solution will last for many moons to come

Final product. The foil weather tape appears to stick best of all to aluminum – the firewall’s covering is aluminum so I have high hopes that this solution will last for many moons to come

______________

The other associated project which had to start with the dash removed: installing the RAAMaudio soundproofing my mom and I got as a gift to me (both as congratulations for getting the job at McMaster-Carr, and as thanks for the huge amounts of work around the house and yard I have done).  The firewall, between the engine and the cabin, is one of the biggest areas for sound transfer into the car, so it made a lot of sense to tackle this project at the same time (as I NEVER want to take the dash out again, if at all possible, thanks):

The RAAMMAT in place after a good 2.5 hours of removing the old stock sound deadening, oy gevalt

The RAAMMAT in place after a good 2.5 hours of removing the old stock sound deadening, oy gevalt

Stay tuned for updates here both on those DIY projects, and the soundproofing as a descent (further) into project madness.  Though it is unfortunate I won’t have the car fully done by the start of work at McMaster on Monday, I much prefer to do all the tasks right and fully, and use my folks’ Excursion in the interim as my daily.

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