The Webasto AirTop 2000 D is a type of electrically operated diesel fueled space heater. These are found in large trucks, RVs, construction equipment and boats. They are popular in tractor trailers because the truck's cab can be heated without having to run the engine. Depending on temperature settings a unit can run 24 hours on less than a gallon of fuel.
There are two different German companies that have most of the market for this type of heater between them. Webasto is one and Eberspächer is the other. In this country Eberspächer markets it products under the name Espar. New units are pricey but there are usually some used ones for sale on ebay. These heaters are also available in a gasoline/petrol/benzine fueled version but since those are more popular in Europe they don't show up as often for sale on ebay. On this side of the pond the diesel fueled version is mostly used.
Step 1: Start Disassembly
Remove the Heater Air Inlet and Outlet Covers.
There is a trick to getting the cover off. Lift up on either side of the cover just enough so the small lip clears the edge. Then slide to the side. It will release. Do the same for the Outlet Cover. Remove the Upper Housing Shell.
There are four tabs (two per side) that secure the Upper Housing Shell to the Lower Housing Shell. Squeeze above the tabs on the Upper Shell while pushing on the tabs with the screwdriver. It will pop right off.
Step 2: Remove From Lower Shell
You'll have to lift the Heater Air Intake from the Lower Shell at the same time. Put the shell off to the side and place the heater back on the mounting platform.
Before preceding I want to point out a few things. Wrapped around the Heat Exchanger is the Insulation or more appropriately in this case, what's left of it. The Webasto repair manual name for it is "Insulation" so I'm assuming it's original purpose was to insulate the Heat Exchanger from the plastic of the outer shell. All that's left of mine is a thin metal band and some felt-like material scraps.
On the top of the Control Unit there is a small round electrical component wired into the X9 Connector. This is a 10K ohm thermistor. A thermistor is a type of electrical resistor whose resistance changes with temperature. It's what the heater uses as it's air temperature sensor. If you were to wire up an external temperature sensor, this is where you'd connect it.
Also on top of the Control Unit is the CO2 Adjustment. From the manual: "The CO2 contents of the exhaust is adjusted with the potentiometer on the control circuit board.The air heater is preset by the manufacturer with respect to the combustion and heating air fan fitted. After adjustment by the manufacturer the potentiometer is in center position." When a heater is changed for high altitude operation this is where the adjustment is made.
Step 3: Remove Control Unit
A quick word about one of my little helpers. I take a plastic ice cube tray that was no longer used since it had started leaking. Write sequential numbers above each "cube". As I take something apart I place the screws in the tray in the order that I remove them. Helps greatly with reassembly.
Look to the side where the two pairs of wires are underneath this clip. One pair is yellow and the other pair isn't. Slip the wires out from under the clip.
Step 4: Remove Combustion Air Fan
Very Carefully separate the Combustion Air Fan from the Heat Exchanger. There is a gasket separating the two parts that might be reused if handled carefully. The heater oval base and Heat Exchanger are cast as a single piece. You can see the gasket stayed attached to the Heat Exchanger.Since the fuel pump wiring is part of the Combustion Air Fan the wires must be pulled up through the base to completely separate the Combustion Air Fan from the Heat Exchanger.
Set the Combustion Air Fan off to the side.
You can see the gasket stayed attached to the Heat Exchanger. Very gently pull the gasket away from the Heat Exchanger. No tools needed. Be careful not to bend it. This one is in good enough shape to use again.
Step 5: Remove Burner Insert
The two sets of wires pass through the side of the Heat Exchanger inside Cable Grommets. Push the Cable Grommets through the side of the Heat Exchanger using my finger. No tools needed. After pushing the Cable Grommet through pull the wire in after it. The X connector at the end of the wire will fit through the Cable Grommet hole.
Remove the last two screws securing the Burner Insert. After removing all the screws the Burner Insert is still held in place by the fuel tube that passes through a rectangular Grommet. Very Gently pull up on the Grommet with a pair on needle nose pliers. Pay attention to the Burner Insert while doing this. The Burner Insert should raise along with the Grommet.
You can see the the inlet end to the fuel tube where the fuel line would normally be attached. The Burner Insert can't be raised any higher since that fuel tube's movement is restricted by the oval base plate. Looking a the edge of the Burner Insert and you can see it's stuck to the Combustion Tube. Use a screwdriver to gently pry them apart.
Once the Burner Insert is separated from the Combustion Tube let the Combustion Tube fall back into the Heat Exchanger. The Burner Insert can now be tipped up and out.
Step 6: Burner Tube and Glow Plug
Let it soak for a couple days without any success. Tried everything I could think of to try and finesse the Glow Plug out and it just wouldn't come free. Never having messed with one before I didn't know how much force I could safely apply. It's a least $60 to replace if I wasn't careful. Had an idea. I fabricated a cable so I could hook the Glow Plug directly to the 12 volt batteries. Hooked it up to the batteries until it glowed red. Took but a few seconds. Waited till it cooled down then the Glow Plug popped right out.
Step 7: Combustion Tube and Heat Exchanger
There is not much left of the gasket that fits between the Heat Exchanger and the Combustion Tube. Use a razor to remove the old gasket. Dump out the gasket remains.
At this point the heater has been completely disassembled.
Step 8: Begin Cleaning
The Glow Plug has carbon buildup crusted over it's entire length. Used a utility blade to carefully scrap it clean. Clean out the inside of the Burner Insert where the Glow Plug is positioned. I'll be using a old can of Carb and Choke Cleaner. I say old can since none of my vehicles have carburetors anymore so this can was just sitting around getting rusty.
Use a single edged razor to clean the remains of the gasket from the Combustion Tube. Clean up the edge of the Heat Exchanger with razor. Use sandpaper to remove the last bits of the gasket that I didn't get with the razor.
Use the carb cleaner and a small wire brush to clean out the inside of the Heat Exchanger. As the name implies this where the heat from the combustion is transferred to the inside of the vehicle. It's also where soot will collect. Soot buildup on the heat exchanger will reduce heat transfer efficiency. A clean heat exchanger will require less fuel to get the same amount of heat.
The inside of the Heat Exchanger will look much better when done.
Step 9: Gaskets
To repair the heater I ordered Gasket Repair Kit 82302a from a local truck supply business which is my closest Webasto parts seller. With shipping it came to $37 and contained three items.
First item is the rubber pad that goes beneath the heater. The repair manual calls it a "seal" but parts manual has it as a "gasket". The old one is still fine.
Next item is the gasket that fits between the Heat Exchanger and the Combustion Air Fan. If you remember I was real careful when separating the two parts so I could reuse the gasket. I'll be reusing the old one.
So out of the three gaskets I bought the one that goes between the Heat Exchanger and the Combustion Tube is the one actually needed to repair the heater. It wouldn't be as bad if I could just order the single gasket but I've only ever found them for sale as a set of three. $37 for the one gasket I need is pretty steep. I don't know diddly about gaskets but bet I can find a better deal. Did some reading and settled on Mr. Gasket 5961 Ultra Seal Exhaust Gasket Material. Currently $17.44 for a 24" x 6" sheet at Amazon.
The new gasket material contains a steel core so making accurate cuts will be a challenge. It took some experimenting but here's the method I settled on for making new gaskets. Trace out the gasket. Then using aviation snips cut out a square with the traced out gasket in the center. Take my Dremel-like rotary tool and put it in the bench vise. It's not a actual Dremel but I'm going to call it that. Tighten the vise just enough to hold the Dremel upright but not damage it.
When I bought the Dremel it came with an assortment of different bits but they aren't all labeled. I'll just call it a cutting bit. Using the Dremel like a router, cut along the inside line of the gasket tracing. Cut while rotating the gasket material in the clockwise direction. I didn't have a deck, like with a regular router, to hold the material as I cut it so took my time. Took some fine sandpaper and dressed up the inside edges. Use the aviation snips to trim along the outside traced line.
To make the holes in the gasket first drill a little larger hole in a scrap wood piece. Draw on the crosshairs. The crosshairs help line up the drawn circle over the hole. Drill through the gasket material. After drilling look closely to see if any of the metal core is sticking out through the hole. A little work with a round file will clean it up.
The hand cut gaskets looks pretty close to the original product. Once I got the hang of it I found I could crank them out fairly quickly. I could probably get 6 gaskets out of this one sheet of material which brings their price down to $3 each.
Before any one asks, I have reassembled the heater and ran it several hours using the new do-it-yourself gasket. It runs just fine. There is a difference in the thickness of the DIY gasket when compared to the original. This will necessitate an minor adjustment during the reassembly of the heater but I'll cover that.
Step 10: Begin Reassembly
Notice that the Glow Plug is slightly oval. Place the Glow Plug so the wide part of the oval is parallel to the face of the Burner Insert. The wire contacts should face towards the open end of the burner tube. Install the Glow Plug's hold down screw. Don't over tighten it. Slide the Glow Plug wires into the groove on the face of the Burner Insert.
Treat the Rubber Grommets with Armour-All. Place one of my DIY gaskets into the Heat Exchanger. Put the Combustion Tube into the Heat Exchanger. It will only fit one way. Maneuver the Burner Insert into the Heat Exchanger. Mind the metal fuel tube.
As the Burner Insert is lowered into the Heat Exchanger the fuel tube grommet must be slid into place. I've used Armour-All on the grommet so it slides easier. Be sure the grommet is completely seated. The two sets of wires are next. The grommets will be fitted into the two holes in the side of the Heat Exchanger.
Be sure to run the Flame Sensor wire between the face of the Burner Insert and fuel tube.
I've highlighted this step since I got it wrong the first time. Didn't realize my mistake until the heater was completely assembled and I looked back at the photos.
Here is the only change I had to make because of the DIY gasket. The yellow wires were originally wrapped around the Spoiler one time. The DIY gasket raised the Burner Insert just enough so the wires made contact with the spinning face of the Combustion Air Fan. This was easily fixed by running the wires under the spoiler and not around it.
Step 11: Combustion Air Fan
Step 12: Final Assembily
Clean the Heater Air Intake. There's a small lip in the Lower Housing Shell that the Heater Air Intake fits into. As the heater is lowered into the Lower Housing Shell the Heater Air Intake has to be fit both onto the front of the Combustion Air Fan and behind the small lip in the shell. There is a small round catch on each side of the heater. It needs to pop into the corresponding hole on the Lower Housing Shell.
Next up is the Control Unit. Look down between the heater and Lower Housing Shell. You can see the Arrestor Groove.
The bottom edge of the Control Unit fits into that groove. Be sure it's properly seated before screwing into place. Next are the X1 through X5 connectors. Remember that the color of the sticker matches the color of the wire.
Before I put the heater into the Lower Heater Shell I should have mentioned again about the Insulation strip. As you can see from the picture the Insulation had deteriorated badly before I removed it. Since the heater ran fine with it in this shape I figured it could run without it. Didn't replace it.
Clean the Upper Housing Shell then snap onto the Lower Housing Shell. Slide the Heater Air Inlet and Outlet Covers into place. Install the seal gasket onto the bottom of the heater. That completes the heater rebuild. Here's some odds and ends.
I used the new seal gasket but will keep the other two new gaskets as patterns.