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Eberspacher D1L Service and Repair.
It is probably only necessary to service a D1L when there is a problem. Servicing should be straightforward unless parts have corroded or seized. The glowpin screen is fixed inside the burner and not replaceable. Chemical cleaning the burner should also clean most of the deposits from the screen. You will require one new gasket.

As we had no information on servicing a D1L we bought two 24V D1L heaters sold for spares on Ebay. The ECUs and fuel pumps were not included but it was never intended to get them working again. One of the heaters was 12 volt but was in a case with a 24 volt Eberspacher label. This was ironic, the ebay seller sold them because he had bought 24v spares instead of 12v by mistake. One fan could be rotated by hand but was far stiffer than it should have been. The dismantling photos are generally of the 12v heater plus some from the 24v. The second D1L had a label saying "Starts but wont run", when disassembled it had very black slightly oily deposits inside. This shows there was probably a problem with the fuel. Subsequently we had a further pair of 24v D1L carcasses without ECUs or relays donated to us, many thanks. We have done a full stripdown on our pages but you will usually not need to take the blower apart when servicing.
Release the hood by lifting clear of the pips.
(Photo shows this being done to a D1LCC)
Remove the plastic rivets. With solid head rivets two chisels can lever them out undamaged. Ones with a central pin can be cut off or the pin driven inside, they are usually not reusable. Replacements available on Ebay.
(Photo shows this being done to a D1LCC)
Click on images for better quality.
1   Disassembling Eberspacher D1L heaters.
24 volt version has an extra glowpin relay and internal resistor.
D1L  12 volt version with cpu and relay.
Two D1L heaters as bought on Ebay.
Described as 24 volt spares or repair.
Why one case was held together with plastic ties.
Two rivet holes damaged and a cracked case.
Pull back the cover and remove the nut to release the glowpin connector. It will come away as a single part. Tip:- fit the nut back onto the glowpin so it does not get lost.
Inside the case the glowpin wires go to connectors.
The brown wire has already been unplugged from the 3 way connector. Disconnect the white wire and remove the top half of the case. Lever up the clip holding the connector. A similar clip on the other side holds the cable loom in position. The white connector contains a thermal fuse.
The lower half of the case holds the glowpin dropper resistor. Unplug the black wire from the resistor to release the case. 12 volt D1Ls do not have this resistor, the black wire will be connected direct to the white wire from the glowpin.
Glowpin dropper resistor fitted only on 24 volt versions. This means the 24v version uses the 12v glowpin and takes the same high starting current.
Do not dismantle the resistor assembly unless it is faulty.
The case parts from a 24 volt model.
There is a reset switch on the overheat sensor under a rubber bung on the top of the heater.
Some D1Ls including the 12v D1L we bought do not have the external relay. That relay provides a ventilation mode.
External visual examination of first heater before dismantling. Exterior condition of alloy good, steel parts have some rust. Some connectors have been replaced, this is not unusual for units this old. Fan rotates but considerably stiffer than expected, other D1L fan is better. Heater is 12v version but is fitted in a case with a 24 volt label on it.
Click on images for better quality.
D1L Heater removed from the case. Components: left 3 way connector, center Glowpin, center right overheat trip, right flame sensor.
The manual shows a filter fitted inside the combustion air inlet. Neither of these D1L heaters had one fitted. This is not expected to affect the heater operation.
   Disassembling main body D1L heater No1.
Bottom: left combustion air inlet, center fuel inlet, right exhaust.
Remove the 3 crosshead screws and separate the blower unit from the burner assembly. The gasket is not shown. Some evidence here of water damage.
When we did the second heater we disconnected the wires to the sensors which may be more convenient to do at this time. The loom retaining clip mentioned earlier is visible.
Under the burner front plate are curved air channels similar to those in the fan assembly, this plate is fixed and does not rotate. Easier to see on the picture if you double click on image to enlarge.
The bottom hole joins onto a pipe which goes to the glowpin, presumably to feed air to the glowpin and screen. Also visible at the bottom is what looks like a retaining wedge. This gave a false hope of disassembling that part of the burner before we found two spot welds holding it permanently in place.
Remove the glowpin and check for damage. These glowpins from two heaters are still working but the coils on the one on the right have bent into an S shape. There are localised deposits on that side of the heating coil so it is showing signs of aging.
Page 2 continues with disassembling the blower unit.
Burner plate of second heater after chemical cleaning. The two spot welds are at 11 and 4 o'clock. Also clearly shows air channel fixings.
The gasket under this plate looked like it could be removed but levering on one part only bent the plate. Later we confirmed the glowpin part of the burner has been welded after fitting the gasket so plate cannot be removed. Photos of a faulty D1L burner taken apart are on our Autopsy page which shows this.
The glowpin screen on a D1L is not replaceable and is difficult to see unless you shine a light through the burner hole. For better views and photographs I used a white LED from a damaged torch to get the light source into the best positions. The photo was of the second heater and looked in fairly reasonable condition. If the burner had not been separated from the blower the LED inserted into the glowpin hole showed a lot more detail than direct light from a torch.
There are still some carbon particles on the screen after chemical cleaning but much of the screen looks clear. These screens have a large surface area so should work even if part clogged. The first heater screen, not shown, was far more clogged with what looked like rust but was possibly deposits from the water immersion.
The D1L glowpin is electrically insulated from the body nut and outer case so when testing connect test probes as shown. New glowpins fit D1L and D3L and have 3 washers. The D1Ls I bought did not have the fibre and large metal washers above the black test probe fitted so they may not be needed. Failures of these older generation glowpin types are fairly common, usually failing open circuit. 24v and 12v D1Ls use the same glowpin.
Replacements are readily available.
Glowpin and two views of the standard connector. The physical construction of this glowpin has caused confusion to some users so a simple description may help. The central threaded rod forms one connection and is joined to the bottom of the heating coil. It passes through the glowpin body inside a ceramic tube which insulates it from the top hat shaped part that forms the other electrical connection. That top hat part passes inside more ceramic insulation so it does not make contact with the large nut and threaded body. Its end is welded to the upper part of the coil.
There are several glowpin types fitted in Eberspacher air heaters so if replacing ensure the correct one is bought. Unlike modern Eberspacher heater models the 24v D1L uses the same glowpin as the 12v D1L.
Fuel pump.
These heaters did not have fuel pumps with them.
In the base of the fuel pump is a filter that should be checked.
Details are in the servicing pages of  D2 and D1LCC models.