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Older Diesel Air Heater Models 4 to 8 KW

Eberspacher   D5LC   D5L   D4L   D7L Heaters


The D5L D5LC and Airtronic D5 air heaters use the same or very similar burner, unlike the smaller models which have changed the burner design several times.

The latest model, the Airtronic D5, differs substantially from the other Airtronic heaters as it retains the older D5LC design, only a new ECU and a combined sensor have been fitted. It does not have the lower start current and the easier servicing of the other Airtronics.

The D5L heater has a removable glowpin screen so must have been produced later than the D1L  D2L  D3L & D4L models which do not.

Despite some references to D5LCC heaters found on the web that model has never been manufactured.

Similarly there are no D4LC or D4LCC heaters.

The D5LC label is printed as D5L C so people thinking it is a D5L is understandable.

Also Eberspacher use the letter L to indicate Large for the Airtronic D5, writing it as D5 L.

(No wonder I was utterly confused on these models when I started on this page!)

* Dates are a general indication only, nearly all are very much best guesses as date information is not published.


There is no D5LCC model.


D5LC label is confusing and could be read as D5LC or D5L.

The circuit board on top of the blower can fail due to bad soldered joints where the 12 pin connector is soldered in.

It may also suffer with corrosion.

See servicing pages for details.



Manufactured  ????, replaced by Airtronic D5

[Our manuals are dated 1995 and 2004,

one heater we know is dated 2003.]

Automatic settings           Start   High   Med   Low   Standby.

Heat output                      5500   4800  2700   1200    0  watts.

Fuel consumption             0.68    0.58    0.35   0.15    0   l/hr.

Current 12v approx             6.5      6.5       3        3       0  amps

Current 12v with glow pin on during start        approx 23 amps

Length 526,  Width 179,  Height 194   mm.

Combustion air inlet pipe 25 mm     Exhaust outlet pipe 24 mm.

Start current is double that of D2 D4  Eberspacher Airtronic heaters so needs thicker power cables.

The smaller grommet on the upper case gives access to a rotary valve.

It is in the combustion air feed to set the fuel mixture. Leave it alone unless a gas analyser is available.

The D5LC comes in 5 release versions, R0, R1, R2, R3, R4.

The number should be printed on the ECU.

Only R3 and R4 versions have ECU locking.

The diagnostics work with modern diagnosis equipment like 701 or 801 controllers.

There are also some simpler diagnostics built into the D5LC.

If you connect pin 4 and  pin 6 on the controller (yellow and black/white wires) together for between a half and two seconds the controller light should blink the fault codes.

I believe this signal output will be on the blue/white diagnostics wire.

Download pdf for the details and the output codes.   http://www.avtonomka-bu.at.ua/dokk/Blinkingcode.pdf

I have not tried it as we have no D5LC model so cannot give more detailed advice.

Spare parts availability:  

  Some parts same as Airtronic D5  excellent.

  ECU and sensors different to Airtronic D5  good

Servicing information see servicing pages.

d4l_1_big.jpg d4l_2_big.jpg

Photos George Green.



The donated D7L is about 35 yrs old.


Orange air solenoid in combustion air path reduces the air flowing in half power setting.


D7L control unit on left, impulse unit right.


There is a 20 amp fuse in the Impulse unit base.

Generated pulse frequency  Full 7 Hz, Half  3.5 Hz


Blue block is Ignition spark generator.

Glowpin / spark plug right.

The overheat reset trip which caused the fault on the donated D7L.is lower centre, above the blue crimp connector.


Under the cover.

Switch connections just visible on left.


Two temperature switches.

If the flame does not ignite the safety switch operates after approximately 3 minutes.

Cancel by switching off then on again.

Connector can be unplugged for installing a thermostat locally in the heated air duct.


More photos are on the Airtronic D5 servicing page.

Manufactured  ????, replaced by D5LC ????

No main manual available, specifications unknown.

Photograph the same as D5LC

Parts list shows the D5L and D5LC are very similar internally and most parts excluding the ECU are the same.

Service see our servicing pages.

Circuit board on top of the blower is the same as the one fitted on the D5LC so it may have the same problem.

Photo Mark Fleming

No Installation manual available, specifications not known.

Heater labels seen show dates from 1980 to 1990

These heaters are probably 35 to 45 years old.

The label gives some information:

Current drawn when running about 6 amps.

Maximum heat output 4300 watts.

Parts manual reveals some extra information:

Round orange block on air inlet is an air solenoid.

Full/half switch  4300, 1700?W

On / Ventilate / Heating switch.

Fuel pump rate 200 strokes for 5.5 to 6.0 ml

and 316 to 350 strokes per minute on full power.

Additional info from Rob

For full / half power switching an air solenoid changes air flow.

Blower speed is constant on both settings.

Pump is pulsed by switches operated by 2 cams driven by the blower.

A relay disconnects one cam output for low heat.

If this relay fails pump remains on low pulse rate, heat output on high heat is only 160 deg F instead of about 200.

The D4L is obsolete and no longer supported by Eberspacher.

It has a steel heat exchanger which should be replaced every 10 years as they can split due to metal fatigue, allowing fumes into the heated air circulation.

These heaters are over 30 years old and it is highly likely heat exchanger will not have been replaced. Spare parts including gaskets are unlikely to be available.

Corroded and loose connections are worth checking.

Any other faults will probably be beyond economic repair, replace with a modern alternative. eg Eberspacher D4, D5, D5LC

 We would not recommend buying a second hand D4L.

Modern heaters are better and have an alloy heat exchanger.

Manufactured  1976 - 1990*   [Our manuals are dated 1991, 1992.

Earliest model found on web is dated 1976, nearly 50 years old (s/no 1829)]

Settings                                Start       High        Low.

Heat output                          8000     80000     4000  watts approx

Fuel consumption                1.05        1.05        0.5    l/hr.

Current 12v approx               19          9.5         9.5    amps

Fan speed                          3000 to 3650 rpm

Length  712, Width 245, Height approx 260    without cradle mm.

Weight    20 kg

Combustion air inlet pipe   25 mm

Exhaust outlet pipe            42 mm.

Spare parts availability:  Obsolete  and no longer supported by Eberspacher

The D7L is massive and weighs about 20 kg (44 lbs).

Compare its size with the Airtronic D2 dwarfed below it.

It has a steel heat exchanger which should be replaced every 10 years as they can split due to metal fatigue, allowing fumes into the heated air circulation. These heaters are between about 35 and 50 years old and it is highly likely heat exchanger will not have been replaced.

Spare parts including fuel wicks are unlikely to be available.

Corroded and loose connections are worth checking.

Any other faults will probably be beyond economic repair, replace with a more modern alternative.

We would not recommend buying a second hand D7L.

Modern versions are better and have an alloy heat exchanger.

Ian Tisdale replaced this faulty D7L shown with a modern alternative, thanks for donating it to our collection.The heater would have had supporting cradles at each end for mounting.

There were two similar 6 pin connectors in the loom, one goes to the Universal switch, the other to the larger control unit so these had to be identified. The wiring to the universal switch differed from the circuit diagram, I found these were minor changes to allow the thermostat to switch the heater on / off instead of the full / half power switching in the drawings.

I traced the fault to the overheat trip switch. It was in its normal un-tripped position but the contacts were not making an electrical connection.

On test the D7L started pumping fuel 30 seconds after switch on. It started reliably with almost no smoke so internally in good condition. Noise level was a lot lower than I expected for a heater this size. Blower speed was the same on full and half power.

A modern heater would have been put back in service but at this age it was safer to pension it off. I originally intended to strip it down for servicing photographs but as it is working well and servicing parts unlikely to be available decided not to do so at this time. The number of DIY users servicing a heater of this age and size is going to be very low.

One major replacement part that may be impossible to find or very expensive is the fuel wick, it is called a combustion chamber coat in the parts manual. A similar wick is shown on the D3L service pages. This is the first heater I have met with a glowpin / spark plug, these are sometimes advertised so presumably still available.

Servicing photos

If you service a model we have not fully covered here we would like to incorporate the details and photos to help others. We would need a full set of good or at least reasonable quality pictures and a description of each stage. Ideally photos should be high resolution as possible, preferably the original unedited and uncropped versions, on a cd or dvd if too big to send by email.

I can edit, add arrows etc. We always acknowledge the source of such photos.

If your heater is really carboned up we would welcome detailed photos to add to our pages.

Photos of specific problems are also of interest.

Page 1 covers Airtronic models D2 D4 D5

Page 2 covers older models D1LCC, D1LC, D1L, B2L, D2L, BN2

Page 3 covers older models D3LCC, D3LC, D3L.

Page 4 covers older models D5LC, D5L, D4L.

The D2 is dwarfed by by the D7L.

D7L complete

D5LC_01_big.jpg d5lc_02_big.jpg d5lc_03_big.jpg d5lc_service_31_big.jpg
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