Defrosting - Part 1

No, this post isn't about how to remove frosting from a cupcake or the like. Today's post (and, knowing me, the next several) is a return to the seemingly never-ending effort to clear the windscreen on the old VW bus.

Modern Set-Up

It probably makes sense to start at the beginning. Most folks who drive modern cars do not realize how spoiled they are. The engine is sitting right in front of you, and it is water-cooled, providing a great source for warm air. The defroster system has relatively short hoses to move that coolant from the engine to the heater core inside the little plastic chamber (like the one pictured to the right here) below the windscreen. The heater core is controlled with short cables or little motors controlled from the dash, routing air through short channels into the cabin or up onto the windshield. In my more modern cars, I can push a button and fire up the air conditioner (A/C) and speed up the defrost even faster. You probably knew all that, but still it is important to have that context. One last little bit worth mentioning: the source of the outside air is usually right in front of the windshield up on top. This gives the highest probability of fresh air.

Original VW Bus Set-Up

from JBugs of a Beetle but you get
the basic idea

The bus is not at all like the modern car I just described. We start with the obvious: the engine is in the back and it is air-cooled. Back when these buses were new and before owners got their hands on them, the design of the heat/defrost system was relatively simple. The air cooled engine produces lots of heat, especially off the exhaust manifolds. This is a heat source for all cars, frankly, but the German engineers latched onto the exhaust manifolds for the cabin heat source. They did so by wrapping big metal sheets around the exhaust manifolds and called them "heater boxes". Air was driven through these heater boxes by the engine fan when the engine was running fast enough. Alternatively, there was a "booster" blower fan when the engine was not fast enough. The air was forced from the very rear of the bus through these boxes to a pair of controllers (one on each side) that were activated by a cable adjusted on the dashboard with a pair of levers (one lever per cable). From the controllers, corrugated tubes connected to a "Y" joint, then to a long central pipe up the center of the bus to the front. This picture on the right here shows a slightly different story for the Beetle, but the concept is very similar. At the bus driver's right foot there is a lever which directs the air either to the floor register or up to the windshield.

When it was originally constructed, I imagine that it worked quite well. Unfortunately for many bus owners this system is not typically well maintained. Parts are removed for "performance" reasons (heater boxes are often sacrificed), they deteriorate and fall off (corrugated tubes or air hoses from blower fan) or they just fail (cables). Often the various parts of the system do not connect together as well as they did originally, creating gaps. So, by the time a bus reached even 25 years old, many drivers would not get warm air when they manipulate the levers. Personally, the best I ever got was semi-warm oily-smelling damp air drifting thru the vent with zero urgency. Ultimately, my defroster was a squeegee and a towel I kept between the front seats. When it was cold, I would also keep an ice scraper.

There are many posts and threads about how to restore or improve these systems. The best advice is to start at the back and work your way forward, making sure everything is the way it is intended. Replace the seals, adjust the cables, lubricate the moving parts, etc.

Add-on Blowers

Atwood bilge blower

Years ago, I read a piece suggesting the addition of a 12V bilge blower to the mix of parts. The idea was that if you boosted the CFM, with a fan in the middle that you would get better performance. I found that the bilge blower just increased the rate at which the damp semi-warm oily smelling air appeared at my windshield, ultimately increasing the fog, rather than reducing it. At it's peak, I was able to reduce the damp (by letting the engine get super warm), but there was no way to prevent a flash-fog while driving in the rain and hitting a puddle. Also, no matter how long I ran the engine, once it was cold enough for ice to form, the bus could never get warm enough to keep ice from forming on the inside of the windshield. Now, this could in part be because of door and window seals, but even sitting still, with the bilge blower running with a hot engine the best I could do was hold the ice at bay.

So, I added a "parking heater". No, not like the one I just installed (here). This was a super small electric-coil based home space heater that I left plugged into the AC outlet inside the bus, under the rock-n-roll bed. When I was parked at home, I would run an extension cord under the garage door and plug it into the bus. An hour before I had to drive somewhere, I'd plug in the garage-end and pre-warm the bus. This worked for the morning drive to the mass transit parking lot, but the drive home was still quite cold. Icy windscreen at worst, foggy (queue squeegee/towel combo) most of the non-Summer months.

To help remedy the cold windshield, I got one of those accessory-plug fan things like in the picture here. For the drive home from the transit lot, I would point that thing at the windshield right in front of me. If I stayed at or below 25mph, I could keep a small circle in the center of the windshield clear enough for me to take the backroads home without having to resort to wiping the windshield with a towel. Needless to say, this was not exactly safe nor workable for the long term especially since I had to drive with one hand holding the thing, moving it around to make a big enough circle to see through.

First Defrost with TDI
When I did the TDI conversion, I thought "well, I'm finally gonna have some heat". 10 years later, my first defroster attempt was okay, but it still lacked. When my ignition melted a couple of years ago (See 4Peaks 2018 - Road Report), I thought maybe the fan set up was part of the problem so I ripped the electrical part out. Still, for perspective, it is worth describing what it was.

I bought a used Vanagon rear heater locally in Portland for, like, $20. I set it on the driver-side auxiliary battery tray (left side) and added lengths of 5/8" hose from the heater to the appropriate in/outlets on the TDI. I fab'd a register that fit onto the front of the heater that routed air into a 3" diameter insulated air hose (from McMaster-Carr) which then ran up over the driver axle and up to the front of the bus along the driver-side of the radiator. Just in front of the radiator, I connected it to the original air system. I took the original Vanagon rear-heater fan control and popped it into the dash. I was able to get reasonable heat, but rainy weather continued to be an instant-fog issue. And, the air source was less than a meter from the exhaust pipe, so, when we were sitting still at a traffic light, we would get a nice lung-full of diesel exhaust unless I remembered to turn off the fans when we were decelerating. Considering how it was with the air-cooled engine, this was still leaps ahead. From oily, semi-warm drifting air to warm diesel-exhaust moving with purpose, it was a definite improvement. Now, that the cooling issues have been solved, I can focus on restoring, or rather, improving this system.

That was a lot of context, and not hardly any content. I know. So, I'll spill my plan today, and then next time I'll start on the work. I am going to move the Vanagon rear heater from the auxiliary battery tray under the bus just in front of the radiator. I will route the air through a different custom register into the old air system. Coolant will be plumbed, electrical will be run and eventually a cable to control the coolant flow will be added. I hope. Maybe I'll figure out a way to source intake air so it's not all exhausty nor damp. Big plans. As always, I'm sure I'll have lots of errors and discoveries along the way. I'll do my best to document it as I go.

That's it for today. Thanks, as always for following along--