"Mercedes 'A' Class"
Components Parts
Heater Blower/Fan Units.

Unless your into Classic cars then the days of driving in excessive cold or hot conditions are gone . Most modern vehicles offer very much improved driving conditions with sophisticated heating systems as well as climate control and air conditioning. These require little servicing with the acceptation of a new carbon filter, coolant change to ensure anti corrosion and anti freeze of the system, matrix and metal pipe work and as well as the odd re-gassing Which of course combines the Air Compressor lubricant(oil). See page.31. for Air conditioning.

Warning of scalding by excessively hot water/coolant fluid.

Whether Winter or summer Have driven your car, NEVER release the coolant reservoir cap without first allowing the system to cool for a few minutes and even then take precaution against being scalded by the excessively hot coolant. Cover the reservoir cap with a cloth and remove slowly to allow the pressure to equalize.

In the petrol 'A' Class the heater booster ensure that warm air reaches the cabin very quickly, in adverse whether conditions of heavy frost and snow this reduces the need to scrap the windscreen free of ice providing you are prepared to wait for just a few minutes, this combined with the rear window fitted with an integral heater along with the heated external mirror lenses and heated screen wash nozzles helps to ensure all-round vision is available before moving off
. Driving the car with just small holes cleaned on the various windows and windscreen is of course highly dangerous, not just for the occupants of the car but also for third parties pedestrians, cyclists, etc. not to mention that's it is also a driving offence.

With lights Air/heater/blower switches
Bulb failure, if your heater illumination fails on a 2001 onwards model then the dash has to be partially removed to replace the bulb
If like Steve,see mypage.3 question 206 you loose all power to the heater /blower control panel then if after replacing fuse 45 you still have no power then there is every chance that the ignition switch is the problem.
Simply checking the fuse is not ideal, swop the fuse for one of the same value or replace the fuse to be certain that the fuse is not the cause of the failure.

On pre February 2001 models Only (Pre face lift)
On earlier models the centre heater dial/knob pulls off to expose the bulb. This has to be removed using something like a BIC biro body and blu-tac or a piece of polythene Tube approx 5mm in dia,A Warm one end of the tube to make it supple and gently push it onto the head of the bulb, allow to cool and then withdraw.
Because the bulb is recessed it will have to be replaced in the same way, using something like a drinking straw, insert this into the polythene tube genlty holding the bulb in it is housed position, ease the polythene tube from the bulb lens.
Bulbs are the same as used in the instrument cluster, See mypage 45 these are available from stores such as Halfords and cost approx 1.00 each.

The heater in the 'A' Class is excellent, producing warm air to the front screen etc, (dependent on settings) after only a few minutes of the engine being started.
Very detailed information is available in your owners handbook page 119 (the page may vary in some handbooks)

There is little doubt that the modern heater and air conditioning unit is a very sophisticated piece of equipment, made up of dozens if not hundreds of component parts. all playing their part in keeping the car either warm or cold which ever the occupants desire.

Hot Coolant fluid/water is supplied through rubber hoses to the heater matrix, the blower then directs the heat to the various parts of the car as required by the driver, this is controlled by the right hand knob/selector which directs the air to the areas depicted on the control knob The centre of the three controls controls the degree of heat admitted to the interior of the vehicle, for demisting for instance the right hand selector would be placed on the screen icon , the centre control would be set on the red section and the left hand selector would be positioned to achieve maximum blower this quickly clears the windscreen, in a similar way if the air vents extreme left and right are set to allow air to flow onto the two front side screens these also will remain free of mist or condensation.

If ordering parts for your car you must quote the VIN number as there are several different modifications fitted the various 'A' Class models

Situated forward of the dash are slot air vents which demist the windscreen when the selector is set in the correct mode. Also positioned on the dash are adjustable air vents , these can be open or closed as well as adjusted so as the air flow goes either up /down /left or right again the intensity of the air distributed depends of the dial settings and the setting of the air blower/fan

If removing these units for replacement purposes ensure that the connecting sleeve which locates at the rear of the unit is in place before re-installing the vent, failure to do so, and apart from another rattle on the car due the the loose connection piece, you will not get forced air coming from that vent when the blower is on with vents selected, & settings open

Link for additional information:-
Air vents removal & replacement

Diagrams showing the settings below can be found in your owners handbook pages 119-127

However for those Owners who have not had the handbook passed onto them by the previous owner the following setting are displayed for the various conditions the white line on each of the dials being set as shown.
In all cases adjust the controls to suit the occupants of the car.
Talking over a fan that is permentally on full blast is annoying to say the least, as is being frozen to death by the owner who tries to impress you with the efficiency of the air conditioning.
If the controls are used efficiently the modern vehicle can be a very comfortable environment for all passengers, allowing you to get away from the cold of winter and the heat of summer.

Do remember that some models do not have air conditioning, also the part the Activated carbon filter plays in air conditioning
If you do get smells from the outside environment whilst driving turn off the Air Recirculation button straight away.
For details for changing the Activated Carbon /Pollen filter which applies to cars with and without Air conditioning see mypage 23.

Do remember that when the light displays on the button on the left the 'Air Recirculation' is ON

However when the light shows on the Air Conditioning (AC) button Air Conditioning is OFF

Basic Heater Settings Winter
Set the controls as shown,
Close the central air vents, Set the side air vents to half open, with the expelled air directed onto windows.

Maximum Heat output (Winter)
Set the side air vents to half open
The air flow directed onto the side windows.

Basic ventilation (Summer )
Turn the air flow as required, to at least position 1 (one)
Open the centre and side vents as required

Misted up windows (Inside)
Close the centre vents,
Open the side vents and direct them at the side windows.
Note that the 'Air Recuirculation' has been turned, ON
This is indicated by illumination of the small light built into the button.
To turn off 'Air Recirculation press the button again and the light will go out.

Windscreen misted up on the outside.
Switch the Wipers ON
Stopping them as soon as the moisture is cleared
Running the wipers on a dry screen is likely to damage the rubber composite blades and cause unnecessary wear.

Special settings use for short periods only
Only select for short periods /Defrosting
Open the side air vents and direct them at the side Windows.

The controls are simple to operate and the heater as well as the blower are very effective, the air being distributed from air vents situated in the forward of the dash to direct onto the windscreen, vents are also fitted centre, and to the side of the dash 1 and 2 ideal for direction onto the side windows, these vents can also be controlled or shut off using the facility available on each vent. Inside the driver and passenger doors at the end of the consul/dash there are non controlled vents 3 I have not found that these are effective in any of the heater/blower settings.
Fitted at feet level in the rear section, there are two none controlled vents at feet level 4

air flow can be controlled by the blower /heater controls on the dash to these units.

The climate control is monitored by a very small fan in the interior light assembly, it is this unit that maintains the car at the pre-set temperature,( Climate Control) .
The two buttons , the one on the left increases the volume of air being re-circulated around the car, and readily de-mists the whole car, the indicator lamp in the centre of the button being lit when it is ON (operating) ON
The button on the right is the control switch for the air-conditioning system, when the indicator light is lit (ON) this button the air conditioning is OFF

Note this light installed in the AC button will not light if the blower/fan is switched to 0/OFF, move the blowe/fan dial to position one, if the AC is switched OFF the light will illuminate/display.
If the light does not display the AC is ON .

It should be noted that in cars with climate control, this mini fan A runs when ever the ignition is on, and had been known to cause a noise which is difficult to trace unless you are aware of it is presents, a very small amount of lubricant on the spindle of the mini motor cures the noise.

Generally these units are reliable and need little or no attention with the exception of clean filters, and of course the maintenance of the air conditioning units by gas replacement every few years, if we want and are going to get the best from the systems.

Things you are advised NOT do do when the the car is frozen up:-
1 Do not pour boiling or hot water onto the windscreen when frozen, this can cause the screen to burst.
2 Never lift the wipers off the screen while frozen , this can tear the feather edge of the blade rendering them useless.
3 Never active the windscreen wiper motor this can cause damage to the motor, arms, and blades.

During extreme weather conditions allow your car to warm up before driving , I have had several instances where having just pulled away the screen has fogged up severely causing me to pull over to clear the screen by hand, condensation is always drawn to the coldest item in the environment, the windscreen being the coldest will attract the condensation causing severe visibility problems, I 'm quite sure that many drivers like myself have seen cars being driven with the windows fully fogged up or only partially cleared of ice, snow, and condensation this is not only highly dangerous but also illegal as your vision is impaired and can lead so easily to an accident. Two minutes spent before you start your journey can save you hours of stress and regret if you are involved in an accident due to your inconsideration for other road users.

Do remember to provide your Vin Number when purchasing spare parts , this ensures you get the correct component for your individual car.

I am only aware of a small number of faults on the heater system:-
Bulbs that fail leaving the heater controls unlit, these can be easily replaced on the pre facelift model by removing the centre control knob, NOT SO ON THE POST 1/3/2001 model, where I feel sure you will have to remove at least the control module comprising of the three controls and two buttons. Blower relay which if fails runs the blower fan at maximum speed , altering the setting of the blower control has no effect. So you are left with a blower/fan that will only run full on or off. This is not an insurmountable problem although Mercedes-Benz workshops have been know to quote an absorbanent amount running into a three figure sum to correct this defect having claimed to the owner that the dash/heater had to be removed, this is not the case on the facelift model
The Relay is a plug in unit, and can be got at by easing the carpet on the off side back and replacing the relay. Most of the work is done by touch so take care to familiarise yourself with it is location before removing the defective unit.
Lets explain what happened and warn you of the possible problems associated with diagnoses of problems on your car by the manufacturers.

These systems are usually compact being integrated with the fascia ,dash and centre consuls of the cars interior, not by any means easy to work on should something go wrong, so much so that in some circumstances the whole dash assembly has to be removed to just replace a air flap motor and component part, sometimes even a small bulb!

There are rubber pipes involved in the heater system, ensure the clips are tight and not showing signs of leaking, also as you car gets older keep an eye open for signs of perishing, a hose replaced in the garage can save you hours at the roadside following a breakdown. Remember the hot fluid circulating in your heater is also the coolant for your engine when the system fails you loose both and the car becomes unusable.

Heater blower

I should be noted that when the heater blower resistor goes defective the blower will blow as though on full, the resistor allows the blower speed to be controlled using the switch.

Andy the proud owner of an 'A' Class W168 LWB 2003 A170 suffered problems with his heater blower, which for reasons best know to itself would only run when switched to the Full ON , ideal for clearing the screen at this time of year (March) but not something you want on all the time, and yet some air flow throughout the car is necessary. However being an enthusiastic and caring owner he sought the help of his Mercedes-Benz Branch
Andy knew the problem wasn't serious, it was more inconvenient, you could de-mist the screen alright but then had to put up with the blower on full all the time you were driving or turn it off. For some reason the blower would not run in the intermediate positions on the dial.
Andy decided to get it fixed where better than Mercedes-Benz.
Just one more job in the life of a Mercedes-Benz technician complete with white gloves! looking for and dealing with the faults on owners cars.
But first of course a diagnostic test was required to try and ascertain the problem.
They had the car in and carried out some tests and did the diagnostic test, no problem the blower resister was diagnosed as being faulty and would need to be replaced.
Andy had visited Mercedes garages before so he was well aware that little is done for less the a couple of hundred pounds and so was prepared for a bill and about that cost.
However when he went to collect the car, the initial test and diagnostic test was billed at 112. and that was only to locate the fault which had at least been identified. Albeit the branch concerned did not have the part required to undertake the repair, which as it turns out was a saving grace for Andy's wallet and bank account!
He was now advised of the problem and of course handed the bill for the work already undertaken, on which was the quote to carry out the repair the grand sum of 420 87 to replace one small resister, mind you that did include the VAT at 17.5% when he queried the cost he was told the centre consul had to be removed. which would take several hours.

Andy was a little more than 'taken a back' he paid the initial bill and & collected the car, he did however order the part specified as being defective because it obviously had to be replaced at some stage by some one, if the fault was to be corrected.

One resister Part no A168 820 00897 (Valeo PA 6) at a cost 23.94 +vat of 4.19 was ordered.
Andy gave this matter considerable thought and finally decided that he wasn't going to pay out that sort of money for something he could possibly do himself even if he did have to get information as to what was involved before hand.
The part duly arrived; in the meantime Andy had searched the internet and found the information he required but if it took a trained Mercedes-Benz technician 3, 1/2 hours based on the estimate of 85 - 100.00 per hour! Well that was going to be some job for somebody who had not undertaken such a task as this one before, although he was aware he had a mechanic friend who had said he would give him a hand! Just as well because this by all accounts was not going to be an easy job? He might well want both of his mates hands!

The carpet is very thick and stiff and will need to be propped back to enable you to work behind the partition.

Please note the car in the photo above is my manual gear box car, Andy's car is an automatic and so the job of pulling back the carpet was even easier!

Andy used his internet source to find out what was involved, and much to his surprise and that of his source, the job involved pulling back the carpet on the drivers side,

Andy duly followed the information supplied, Using a suitable mirror look for and locate the resister housing which is towards the bottom and right of the centre consul, this Andy did without a problem and within 20 minutes was able to e-mail me to confirm that the resister was fitted and that the blower was now working normally, needless to say he was overjoyed at not only having completed the job himself but also because he had saved himself 420.87, in Andy's words, "A lot of beer vouchers in any bodies money"
Andy hasn't told me what his mate said when he told him? but one things for sure pulling the dash etc from any modern car is a real trial without very specific instructions and it is so easy to damage what these days is only plastic mouldings, so it was a blessing that it didn't have to come out!

The photos below are true to size of the resister 8.5cm long, 6.5cm at the widest point

When fitting this unit the lug A goes to the bottom and subject to there being sufficient wiring (loom) length available, remove and re-fit the multi plug (4 spade connection)into the new resister after removing and before installing it into its housing, remember you are working blind, so take you time; remember also what you are saving in s based on the quote and cost of diagnostics above you will be saving yourself over 35 + per minute so you can afford to take your time, and obviously doing the job yourself is very worthwhile.

The moral of this story is if you have problems with your car and you get an estimate that you feel is totally unreasonable then get another estimate from another Mercedes-Benz Branch, I have contacted my branch this morning and asked what it costs to fit this resister and have been told 1/2 hours labour plus vat, my branch charge 85.per hour. plus VAT. I make that a cost of 50.80 Just a little bit different from the rip off price of 420.87, so much so that I wondering if Andy's bill should have read 42.87, and as happens! an odd '0' just happened to appear on the end?

We will of course never know because Andy did the job himself and I recommend that if you have the same problem you do the same. I hope the guidance below along with the photos will help you achieve just that.

Thank you Andy for your input into this page.

However there are still defects that you may well come across on your car . One is the failure of the light bulbs that illuminates the heater dials, although to date I have not heard of a failure on a face lift model.
With the pre-face lift the centre dial pulls off ( can be difficult to get off) and the bulb can be replaced on the 1/3/2001 model (face lift ) it doesn't I suspect you will have to undertake a removal of the centre dash heater controls to replace that bulb.

Again a problem but so far only identified on the pre 2/2001, Air Flap actuator Motor./Shutter Defect, I'm unsure of the exact cause it could be a damaged plastic flap of defective motor.
Flap-clapping noise coming from behind the centre dash, just after the car is started and before it warms up, it is believed that this is caused by defective motorised flap on the side of the heater system.
Again Mercedes are charging over 400 to remove the centre dash and correct this fault.
However before committing it is worth looking at mypage 23 and if you feel up to the job remove the activated carbon filter, having removed run the blower/fan listen for the troublesome noise.
If you get the noise without the re-circulating button being pressed to ON, then there is the possibility that the noise is being caused by the 'Air guide baffles' situated below the motor, Mercedes indicate to remove the motor and reseal the baffles using MB parts sealing strip A170 795 11 98 I doubt there is any thing very special so take a look and if you see loose baffles which run from front to back across the housing re seal them, replace the motor and having allowed the sealant to set test before replacing the remainder of the components. UNDER NO CIRCUMSTANCES OPERATE THE WINDSCREEN WIPERS OR YOU WILL LOOSE YOU BLADE SETTINGS. I understand from owners that this noise only occurs when the ( left hand button) heater control button is pressed (red light on) If this is the case then unless you are able to do the job yourself, Look out for the BIG bill. Or do without that facility until you can find a competent mechanic who can do the job cheaper. If this problem arises on my own car I will be checking to see if the defective component can be replaced from front Activated carbon filter access point It is certainly worth checking.

Over recent months several owners have comments about a slapping sound coming from their blower units when the re-circulation button is ON.
Mercedes Workshops have been contacted by a number of owners who have been told that it is flaps on the blower motor assembly and that the dash has to be removed to undertake the repair which would cost with labour, 100s of .

It appears this only happens while the car is cold and no real explanation has been found. I have said that by removing the carbon filter it may be possible to see the problem however none of the owners have come back with any information to confirm this either way.

While changing my Activated Carbon Filter (see page 23 )I took the opportunity to not only clean the impeller of the blower motor which proved very worthwhile but to also investigate where these flaps could be?

When the motor is not receiving power the flaps are fully open and the impellor can be clearly seen, I didn't check to see if there was any reaction to the ignition be turned on, I suspect not.

When the blower was operated with the re-circulation function OFF the flap adjusted leaving it open about 25mm i.e. Air was still drawn in through the activated carbon filter to the cabin.

When the air circulation button was pressed to on ,I.e. Red light showing the flaps closed completely .

I'm firmly of the opinion that it is these flaps which are causing the problem on a number of owners cars, The cause for the flapping is a different matter. It could be something as simple as a dirty seal or something more sinister, certainly investigating if you have the problem on your car.

If it was my car I would investigate it further by removing the filter housing from which appears to be stuck with adhesive strip, removing the frame would allow you to get at the Torx securing screws more easily , the motor complete with the flap mechanism could then be removed for inspection and test.
It is not possible to remove the screws without first removing the filter carrying frame
Caution would need to be exercised as I'm not sure what's attached to the motor /blower assembly apart from the obvious electrical supply cables which supply the motor.
If one can believe what MB are saying then the dash has to come out to correct the problem, but with respect where its due, we have heard this before somewhere! When in fact it was a five minute job, (See above heater blower resister.)

However David a fellow owner has sent this photo to me, he has the above problem so removed the glove box, which revealed that the gear wheel attached to the motor dash side was split, this would be a difficult component to get at and replace even if the item was available, Looking at the detail of these components it looks as though the whole lever assembly comes as a kit at what price is anybodies guess, David is going to attempt a repair using industrial adhesive I will let you know how he get on .

This E-mail has been received (23/08/08) from again from a fellow owner:-
Since the posting of my findings and photographs were posted.

Dear Lofty,
First of all thank you for your website.
My 2002 'A' Class started to have the Flapping sound from the Blower Fan motor so I decided to take it apart as you mentioned in the filter change page.
I got to the motor and to my surprise it was the motor making the sound and then stopped working. I took the motor out to find that one of the Carbon Brushes was stuck in it is guide and that it was melting the plastic guide.
This along with the worn carbon brush was preventing it coming firmly into contact with the armature of the motor causing the motor stop and start.
It turned out that it was this that was cause of the flapping. Having removed the motor I took it to an air conditioning expert who told me that a lot of the 'A' Class have had exactly the same problem and the new motor's have been modified and have a different design for the brush guides.

I removed the old carbon brushes and replaced, the motor is working fine. I know it will not last because it is a design flaw/failure.

This is as I suspected, and this along with the information about the the heater blower resister above clearly shows that Mercedes Workshop's really do not no what they are talking about when they say the dash has to come out to cure these faults and in the bargain quote 100s of in labour costs for doing so!
It really is time they got their act together and stopped giving owners false information.
Just because the 'Star' diagnostics is not capable of detecting a mechanical failure they come up with some cock & bull story about the dash having to come out.
Oh dear where have all the mechanic's who work with the hands and think with their head's gone?

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