by Joe Helwig
(**Bracketed  corrections were made by Thomas Johnson when Joe's email originally appeared on the bus mailing list.)
I have enclosed my 'standard' spiel about the B2 model. When working on gas heaters, practice safety. Do things slowly, and think about each step before doing the procedure. Gas heaters are great winter heaters if they are maintained. If they are not maintained, they can be dangerous. Never fire up a gas heater UNLESS you know its history, AND/OR you have completed all the gas heater systems checks. ALWAYS have a fire extinguisher, and ALWAYS work in a well ventilated area. If you have done extensive work on your vehicle and you are comfortable being your own mechanic (ie: rebuilding engine, rebuilding carbs, etc), you should be able to tune up a B2 model gas heater. If you are uncomfortable with tuning the heater, take it to a pro. It's better to pay out some cash than risk blowing yourself up. Now with that out of the way...
The B2 model gas heater is a 12 [or 6] volt system. It's mounted on the drivers' side of the car (bug/ghia), and is turned on by a lever in the passenger compartment (near the hood release). When the lever is pulled, the gas heater is turned on. The gas heater uses a low volume, low pressure electric fuel pump to deliver the fuel from the car's gas tank to a jet in the gas heater, which restricts how much fuel is delivered to the combustion chamber. Any excess fuel is rerouted to the car's gas tank. The ignition source is a 4 volt glow plug [hooked up to a series resistance]. Air for the combustion chamber is sucked in from under the front of the car. The exhaust is passed thru the fender well, and released in the wheel well. The intake air is sucked from inside the car's cabin, passed thru a heat exchanger (combustion chamber provides the heat), and blown into the car - it is a recirculating heater. [Most are non-recirculating. I think (but can't yet prove) that '70 was the only year for a recirculating B2.]
A thermostat kicks the fan into high speed when the air is warmed to temperature. When the lever is pushed in (heater is turned off), the fuel pump and glow plug are turned off, but the fan motor keeps working until the air is cooled down. Gas heaters do require routine maintenance which includes: cleaning the contact points on the fuel pump; cleaning the glow plug; cleaning the jet; inspecting fuel lines for cracks; cleaning the combustion chamber (carb cleaner - the kind that is added to gas tank); and inspecting the exhaust system for rust. [Quote from the B2 manual regarding the event of a breach of the heat exchanger: "Since the static pressure on the fresh air side is higher than on the gas mixture side, exhaust gas cannot blend with the fresh air, even if the heat exchanger is not hermetic, and any danger that such gasses may enter the passenger cabin is excluded." This is true for all Eberspächers.]
To install the heater into a Type I, (BN4 heaters are usually installed in busses) you will have to cut the following holes:
- combustion chamber air intake (fender well - 1" diameter), - combustion exhaust (fender well - 2" diameter), - recirculate air intake (underside of dash 3.25" diameter), and - heated air vent (underside of dash - 3.25" diameter). - control lever (near hood release - 0.25" diameter)
You will also need to put a 'pickup' in your fuel tank (mounts on the top of the fuel tank) to feed fuel to the gas heater, and to return unused gas. This would involve drilling a hole in the top of the fuel tank (scary, eh - do not do this to an old gas tank). You can get around this by getting a fuel tank with one already installed, or getting a professional to drill a hole in a new gas tank.
The wiring is very simple - you connect the power wire to the fusebox (a fuse that is always 'hot'- #8 in the early bugs, #7 or #9 on later bugs). You also have to connect a ground wire."
The following instructions are for the B2 model ONLY. Different models have more/different safety systems, and consequently, different procedures. I have 'developed' the procedures from tuning up gas heaters for myself and for my friends (never for profit, though).
You can check the gas heaters parts separately, but you will need a well ventilated area, and have a good 12 volt power supply (a car battery fully charged works nicely), as well as a fire extinguisher (hey, you never know...). I always pull the heater from the vehicle prior to inspecting it. After removing the heater from the car/bus, make sure that there is no residual gasoline left in the heater. Test the fuel pump by removing the power wire from the pump. Give the pump 12 volt positive, and ground the heater case with the neg wire. It should make rapid clicking sounds. The solenoid electro-magnet) pulls the diaphragm up. As the diaphragm moves up, it causes a set of breaker points to open - power is cut to the solenoid. A strong spring causes the diaphragm to move down, and the points touch each other, causing the diaphragm to go up. The up/down movement of the diaphragm is what pumps the fuel. The clicking sound is the diaphragm moving very quickly. When the heater is running, the diaphragm 'clicks' when the back pressure of fuel becomes low (the jet restricts the amount of fuel delivered to the heater).
If it doesn't click, remove the pump from the heater. Open up the pump. Look at the rubber diaphragm, and inspect it for rips/tears. Look at the solenoid, and look for cracks. The fuel pump relies on breaker points to actuate the solenoid. If the solenoid is not actuating, it is due to a fried solenoid (bad - toss solenoid), fried points (scavenge points from another fuel pump) or to the points not being set properly. To set the points, I rely on trial and error. I started with a wide gap, and then tested the pump to see if the pump actuated. I kept closing the points down little by little, and testing each setting. Eventually, I got to the 'proper' setting. I did write it down, but I lost the note (doh!). Make sure the points don't have ridges before you try to set them (use a fine emery paper and gently sand the points to remove ridges).
I use ethanol alcohol to test the pump (non corrosive, and non-explosive). Inspect the gas lines and look for cracks. Hell, replace the fuel lines with some high quality fuel lines. With the fuel feed line in alcohol and to the pump, and the return line from the pump positioned over the alcohol so you can see the ethanol being pumped, start the fuel pump. It should click away, pumping the alcohol. Now place your finger over the return line (blocking it). It should NOT click with the return line blocked (if it does, a torn diaphragm or a leaky fuel line is present). If you gently release pressure on the return line, the pump should be clicking, and delivering fuel. The fuel pump test is complete. Blow out the fuel pump and the lines with compressed air (ethanol can eat rubber if it is in contact with the rubber for few days). Put the pump back on the heater, and discard the ethanol. Remove the jet, and blow air thru the jet. Do NOT use a wire to clean the jet, as the size of the jet's hole is critical for the heater to function (if hole is too big, you will flood the heater). Replace the jet, and the fuel system inspection is complete.
Next, remove the glow plug from the heater. I use a Dremel (TM) tool with a wire brush attachment to clean all the rust/crap off the glow plug body, as well as where it screws into the heater. [With the correct voltage applied] it should glow red in about 10 seconds or so. If it doesn't glow, the plug is shot. If the plug glows red, you have spark.
Attach the + to the main power feed on the gas heater. Put the neg wire on the heater body. Pull the lever. The fan motor should start at low speed. On the thermostat bridge there is an adjustment screw. Gently turn the adjustment screw until the fan kicks into high speed. Now push the power lever to the off position. The fan should still be on high. Turn the thermostat adjustment screw until the fan stops. If the fan worked at high and low speed and is not making horrible screeching sounds (bad bearings), the fan is good. If the fan didn't come on, the brushes in the motor are shot or you have electrical 'concerns'. If you have a DVM or a current probe, check the power from: a) the battery; b) from the thermostat bridge, c:) the fuel pump; and d) the glow plug. When lever is in the on position, all the above should be getting power (both fan settings). With the fan on high and the lever in the off position, their should be NO power to the fuel pump and the glow plug.
Now, carefully remove the thermostat from the heater, but keep all the electrical connections on it. With the power lever on, use a propane torch to heat the thermostat sensor up. The fan should kick into high speed. Turn the power off, and remove the propane torch. When the thermostat has cooled, the fan should shut off. Put the thermostat back on the heater. If the fan did not shut off when the thermostat cooled, turn the thermostat adjustment screw until it turns off, and repeat the test.
Now that all systems check out (hopefully), inspect the exhaust pipe on the heater. You may have to go to a muffler place, and have them replace the exhaust pipe. On my '64's gas heater -uncertain model, (not Eberspächer) but it is HUGE- the previous owner extended the exhaust pipe down to the running board. This prevented the exhaust from being blown on the tire, and helps to limit the amount of exhaust that is sucked back into the exhaust chamber/ or back into the car. Inspect the air intake hose to the combustion chamber, and replace if necessary. Replace the gas heater in the car, and start the car. Start up the gas heater (have fire extinguisher handy). The heater should fire up in less than 30 seconds. If it doesn't, something is wrong turn it off immediately, and locate the problem. Allow the heater to vent the gas it contains (it will be flooded) by waiting for at least 30 minutes before you try again.
If the heater fires up, let it run - there probably be lots of smoke coming from the exhaust if the heater has sat for a long time. Let it run until the exhaust smoke clears, and check if it is putting out lots of heat. Turn the gas heater off, and feel the temperature of the air from the fan. The fan should turn off when it is cold. If it continues to run after the air is cooled, adjust the thermostatic bridge screw. I usually use a carbon monoxide sensor (from the private pilot store), and place it so the heated air blows over it. Have all the windows closed, and let the heater work for 20 - 30 minutes. The card should NOT indicate any carbon monoxide. If it does, you have a leak, which could have fatal consequences. I usually have a carbon monoxide detector attached to the 'Oh My God' bar on the dash. I usually add carb cleaner to the gas tank, and then have the heater operating as I drive around. This will clean out both the carb and the gas heater. Of course, you may cook yourself :).