Air heater blowers have impellers (fans) mounted on both ends of the motor shaft. The larger black or orange impeller draws in the air to be heated and pumps it over the heat exchanger. The smaller brown impeller draws in air from the combustion air inlet port and pumps it to the burner. Water heater blowers just have a single combustion air impeller. We would rate motor repairs on modern Eberspacher heaters as medium difficulty, bearings are more difficult than brush replacement. Parts can be easily damaged if care is not taken while disassembling and we advise only taking apart blowers that have failed. Please feedback comments on repairs and repair methods, good or bad, we learn a lot from users problems and experience. If you decide not to repair the blower please donate it to us for experiments and the autopsy pages.
There are 4 main causes of motor failure, listed with the most common first.
1) Carbon brushes wear until they no longer make reliable contact with the commutator. Typical symptoms speed variations, open circuit and intermittent faults, sometimes a smell of ozone due to sparking.
2) Bearing failure. Roughness can often be felt while rotating the shaft by hand and the shaft may have excessive play. Typical symptoms noise, vibration, speed variations, seized motor.
3) Rotor failure. The windings on the shaft are arranged in several segments that are switched by the commutator and brushes. If one segment fails the motor can fail to turn but will do so if the shaft is moved away from that starting position.
4) Commutator damage. Some wear of the commutator is to be expected, very occasionally it could be excessive. Symptoms same as 1 or 3 but far less common.
Eberspacher D2 and D4 blower units. Impellers are fitted on each end of the motor.
Dereks D2 failed several times with fault code 33 Blower speed. Other causes like something touching the impeller were checked. There was no obvious roughness or excessive play when the shaft was rotated by hand so suspicions of a brushes problem. Eberspacher do not sell individual parts, any damage caused during disassembly would mean scrapping the blower. This unit was faulty so we had nothing to lose taking it apart. This is our first repair of an Airtronic motor and minor changes as described will be made when we do another one. Other ways may be as good or better but it worked for us and is a very good starting point. We did try a lot of experiential alternative methods during the repair especially with the brushes. We marked the impellers and shaft angular position before starting so they can be refitted to keep the best balance. That may not be necessary and it may still not balance after repair but we prefer to do it. We marked the position on the end of the shaft by filing a very small notch on the edge. We also recorded how far the shaft protrudes or is recessed for refitting in the same position.
The heating air impeller levered off using two screwdrivers.
View of the splines on the motor shaft.
Shaft and bearing. The four motor case tabs which had to be bent outwards later.
The combustion air impeller is easily damaged. Using two screwdrivers as with the other impeller might work but we were not prepared to risk it. Other methods may also be suitable. Using only one screwdriver often breaks the impeller. Our simple low tech solution used two sturdy kitchen knives.
These knife blades were 1.5mm thick and the gap was only 0.3mm so the knives had to be carefully worked in. After some levering we finally got them passing right through. We could have levered off the impeller using both knives but here we gently knocked in the handles of both knives and the tapering at the handles forced the impeller up the shaft.
Airtronic D2 D4 blower motor repair.
The central boss may split if impeller is not kept reasonably straight during removal.
Three T20 torx screws held the motor.
Motor ready for repair.
The 4 retaining tabs, shown earlier, had it be bent out. They were fairly strong and it took some force. The motor magnets pulled back as the rotor was extracted. The crinkled washer may stick onto the magnets.
Plenty of carbon debris inside the motor created by brushes wearing away.
Magnets and their retaining clips inside the case.
No need to take these apart.
Four clips that located into holes in the side of the black cap had to be pressed in before it was positioned on the vice jaws. It was held by the step in the moulding so the vice was not tight. The bearing was knocked free from the cap. On future repairs we would try to see if it would come free by side to side movement. Otherwise we would use only light taps so as not to move the bearing on the shaft.
Note: The clips have a tendency to move back into position which could cause problems.
Part of the brush moulding which was nearly level with the bearing restricted how far anything could be inserted. The bearing could have been removed like that but we released the brushes to increase the gap.
First part of disassembly completed. The brushes were quite worn. The bearings seemed ok but we replaced them at the same time while we had it apart.
Airtronic models have a magnet mounted in the impeller for checking the motor rotation speed.
Very old model blowers like the D1L can be disassembled very easily, see D1L service pages for details. On some older models the impeller is glued onto the shaft but we don't know if this was originally done or has been done during reassembly after repairs. One user succeeded with a glued DL8C impeller by holding the other end of the shaft in a vice while gripping and rotating impeller with both hands. Applying some heat at the same time has been suggested to soften the glue if that is not successful. Acetone is another suggestion provided it does not damage the plastic, it did not on a D2 impeller we tested.
The black cross moulding removed quite easily.
We also bought 20 of 16x8x5mm Carbon Brushes for £1.58 including post from Hong Kong on Ebay Jan 2015. These are too big but can be sanded down to required size. bargainbrushes.com have closer in size but more expensive.
Airtronic D2 D4 blower motor bearing and brushes replacement.
One of the four clips is slightly protruding at the bottom of the brush moulding. These are shown clearly on later photos of the bearing plate. The cap has one hole showing.
With the brushes out and some maneuvering the brush moulding in just one position moved completely out of the way. We measured the length of shaft protruding from the bearings before removing them, left 18 mm, right 21.6 mm. Check this measurement carefully in case we inadvertently moved the bearings while taking the motor apart.
Most of our readers do not have pullers to remove the bearings. We used the low tech solution we developed for the D1L blower. See that page for more details. The slot was really too wide, we later cut a narrower one. A medium hit on the end of the shaft with a 4 pound club hammer drove the bearing to the end of the shaft. A small drift (metal rod) drove out the final part.
Removing the bearing released the brush plate and gave access to the commutator.
Tip: A tap with a heavy hammer is far more effective than a blow with a light hammer.
The commutator was undamaged but had some wear. Distinct ridges and grooves could be felt all the way across the segments with a finger nail drawn parallel to the shaft. New brushes could have been fitted as is, they would bed in to match the commutator grooves. We preferred to remove the grooves as brushes would bed in quicker and any end to end movement of the shaft could cause slight widening of the brush grooves.
We have no lathe so used an electric drill and a worn 400 grit abrasive disc wrapped round a piece of wood. The wood wedge shape made getting the right width easy. A perfect level finish was not necessary, we sanded off the minimum amount of the copper to remove the grooves. The segment gaps were checked to see they were still undercut before burnishing with a strip of cloth for a good smooth finish. Tip: If the plate had not been removed there is room to reach the commutator with sandpaper wrapped around a thin flat object.
When cutting off the old brush wire cut it close to the brush, not as shown in following photographs. Two springs, top, apply pressure to the end of the brushes. Wires are joined with compression clips. The two black ferrite rods suppress electrical interference.
We have a hook tool to release the spring pressure when removing or inserting brushes but just as easy to use a low tech 30 mm bent safety pin version.
Replacing the brushes can be done without removing the bearings but we replaced both so we could document the process. Replacing bearings is at least medium difficulty, on future repairs we would definitely not replace bearings unless they were faulty.
D2 Bearings are 13mm outer diameter, 4mm inner, 5mm thick. Replacements are described as 624Z 4x13x5. We bought 10 for £3 post free from China on Ebay Jan 2015. We now have some suspicions these are manufacturers rejects and would not buy them again. UK ones with quicker delivery were same price for 2.
Carl Dalmas says D4 bearings seem a little different.
These new carbon brushes were oversized, nominally 16 x 8 x 6 mm. We measured the old ones as unknown x 5.9 x 3.7 mm. The projection on the end of the new brush where the original spring fitted was carefully trimmed off without damaging the wire. Brushes are relatively soft and were scrubbed by hand on a 400 grit abrasive disk on a flat surface, removing material from all sides to keep the wire towards the center. We kept the wire above center in the 5.9mm plane to leave more room for a spring slot. A scalpel held perpendicular to the surface and used as a gentle scraper corrected any sanding slope or unevenness. The spring on the brush plate was moved out of the way before checking the brush would freely slide in and out.
Tips: The outside of the brush is harder than the inside so it required less sanding to remove the same amount of material as we got closer to the required size. We had to be take care not to sand away too much or the brush would be too loose. Sanding carbon is messy, sand on newspaper so you can wrap up and dispose of the dust. Digital calipers make measurement simple and were used multiple times during sanding to check for size and flat surfaces. If the brushes slide into the plate and are tight look for contact marks on the brush surfaces and scrape those away before re-trying.
The brushes are mounted offset to the commutator so the end of the brush needed to be shaped. Using the old brush as a starting guide we found it easier to control the angle using a file instead of sanding. The angle of the point is roughly 60°
Tip: We found it is better to do this after the slots are cut, the wire has to leave the brush at the top when shaped as shown.
This brush had not yet been trimmed or shaped to a curve. Tip: After pulling the brush spring back lift it vertically, it will rest on the moulding instead of returning to the slot. Be careful not to lift it too far. One brush spring is shown here resting on the moulding.
The brush projected beyond the edge of the plate / plate guide and needed further trimming to about 12 mm long. Photo also shows the spring resting on the moulding.
Tips: Maximum length depends on the depth and shape of the spring slot, the spring must be freely pushing the brush towards the commutator so it moves as it wears down. One mistake we made when working with the wires was to twist them tightly to stop stray wire ends splaying out. That makes the wire even stiffer. Make sure you put the brush angle the right way round, the wire has to come out towards the commutator.
Final Experiments were still being done at this stage of the repair.
Due to other interests Website will now probably not be updated till autumn / winter.
As part of our experiments we also tried fitting with only 16.5mm of shaft instead of 18mm protruding. It did fit together but the brushes were too far towards the end of the shaft.
Using the old brush as a guide we shaped the curve roughly using a small round file. For final shaping we wrapped fine sandpaper round the shaft of a drill bit and sanded up and down to match the original shape as closely as possible. The commutator had a small ridge at each edge which had not been removed during smoothing, the extreme end of the brush was narrowed slightly to avoid the ridges and fit flush on the commutator. The brush will adjust for the ridges as it wears.
We carefully cut two slots with a file and scalpel. The first was so the wire would not project beyond the end of the brush. The cross slot for the spring on the old brush was quite wide, we filed a narrower slot. The wire came loose in many of our early trials destroying the brushes, especially as these involved a lot of experiments repeatedly trying different ideas and inserting / removing the brushes. Then we modified the method so the wire was not central and cut the cross slot slightly away from the wire. We did try adding a drop of superglue to prevent the wire moving but capillary action sucked some of the glue up the wire braid making it very stiff. Gluing back a loose wire gave a bad electrical connection.
We had previously removed the second bearing. The replacement was extremely tight and needed very heavy hammering down the shaft with the metal plate. When rotated it felt very rough and obviously damaged. A second one done using the smaller holes in the plate was also damaged. An inspection of the bearings showed the inner section was recessed so the plate was only contacting the bearing outer causing sideways pressure on the ball bearings. We had plenty of spares but needed a change to our method.
We searched for something to use as a spacer, an old 2BA nut in the spares box was the right size, roughly M4 size. Surprisingly we also discovered some bearings from the pack of 10 were looser on the end of the shaft than others, two could even be pushed all the way on by hand. Perhaps the pack are manufacturers rejects. A medium tight one was selected and the shaft lubricated with Castrolease LM grease. The bearing moved easily down the shaft with light taps to its final position with the shaft projecting about 21.6 mm.
The cup washer and brush plate were fitted on the shaft before driving the bearing to leave about 18 mm of shaft protruding. We had to take care not to drive it in to too far which could be a disaster if too small a gap was left for removal. To prevent this we temporarily placed a second piece of metal in the gap. The paving slab gave a solid bounce free surface which was better than using a workmate. Four bricks held the rotor securely upright. Any spare grease was wiped off the bearings & shaft, making sure none got onto the commutator.
We were a little careless during one experiment and lifted the spring too far so it slipped off the moulding and released the tension. We took that opportunity to remove the spring for photographs. Left picture showed how it would look in its final position but it needed more tension, we rotated the spring through 180° and slotted it onto the pillar as shown right.
Then the free end of the spring was rotated anticlockwise, carefully lifting over the obstructions, first one shown left, to its proper position where it entered the slot, right. Re-fitting or re-tensioning the spring would have been extremely difficult if the plate was still in place on the shaft.
Brushes fitted and ready for soldering. We checked the brush springs were properly positioned. The new brush wire was stiffer than the old one so we decided to cut off some of the strands. Next time we will cut the old wire close to the brush so we can use that more flexible wire and join it near to the brush.
The crimp connector was pulled free from the moulding and the old wire shortened. Minimal twisting of the brush wire was used to combine the strands before soldering them to the old wire. The crimp connector was then pushed back into place in the moulding. A quick electrical continuity check between the pins of the 2 pin connector verified the brushes were working ok and it was ready to be put back together.
Airtronic D2 D4 blower motor re-assembly.
We used superglue to hold the wires in the slots before lining up the cutout in the endcap with the moulding. The shaft pushed into the endcap until the bearing pressed against the top of its recess in the endcap. Fitting was not difficult but it did need some fiddling getting the shaft in position. It also took a little work to get the four catches to lock in. We confirmed the brushes aligned with the commutator which was important. We checked the shaft rotated freely and again checked for electrical continuity.
A very small amount of grease was applied to the crinkled washer before fitting it on the shaft. The shaft fitted easily into the motor body. Tip: The washer is magnetic and if the shaft is pulled back it can slide off and adhere to the magnets and not be noticed. Align the slot in the case with the moulding and hold the shaft vertical with the washer end at the top while inserting. The magnets will pull it towards the side but it is easy to guide it into position.
Before bending in the retaining tabs we tested the motor. Pins were inserted into the connector provided electrical contacts. The motor is 9 volts but we started on about 4.5 volts as there was no cooling fan and the brushes needed to bed in. We had a professional variable voltage power supply otherwise we could have used 3 dry batteries.
On test the motor worked but was not as quiet or as vibration free as a good working motor. Some noise was not unexpected, the brushes were crudely shaped and it could take a long time for them to wear to match the commutator. After a couple of hours running we took the motor apart to check the bearings, commutator and brushes. The bearings seemed ok but we have suspicions about their quality. The leading and trailing edges of the brushes had not yet been worn down to match the commutator and there were visible polishing marks on each of the commutator segments but more towards one side showing the brush had not been shaped level. This would be corrected as the brushes bed in. It was as expected so we re-assembled it for the final time.
D3LCC blower motor repair.
Dominic Baldwin told us the D3LCC the shaft of the motor has a spring at the back of the bearing so sliding in a knife had no effect. There was around 10mm forward movement on the fan, he ended up using a couple of wood chisels and a lot of brute force until it finally popped off. The brushes are fitted directly opposite each other on the commutator of this motor, the bearings were easy removed and are 626zz. Thanks Dominic.
When Carl Dalmas disassembled his D4 the bearing remained in the cap.
The cup shaped washer covers the bearing and is also fitted on the D2.
Drive the bearing from the far side, that also forces the washer free.