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ML320 Blend air motor controls

73K views 70 replies 25 participants last post by  vipergts 
#1 ·
I just replaced my blend air motor after a year of tick tick. Installing the new motor I tested it and found that it does not move through the whole range. It moved to the full heat position and would not return from there no matter what the control was set to. I decided that the controls must be bad so I ordered and replace the AC controls. Same result, motor moves and stay in the full heat position.

Out of desperation I opened the old Blend air motor and started playing with it. I noticed that once it moves past a certain point towards the full heat position it just continues to move and will not return. After experimenting with the old motor I found that I can change the gear position so that it hits the stop before it reach the point of no return. Once I set it like that I only had 90 deg movement in the motor. I did the same to the new motor and it now operates although only partially but I have heat and full AC. Neutral position on the control is now to the left of the white bar on the control.

I figured that it has something to do with the stops not being set correctly but without the dealer's software who knows.

Has anyone had this issue before or am I the first one to encounter this?
 
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#3 · (Edited)
yeah i got sick of this too....put a "rod" over the level and drilled a small hole in the glove box. "manual override" ;)

ohh and yes i encountered it but i doubt my solution will help you... from what i could see was that the flap was actually position to the furthest position in the back on the motor tried to keep going. So i just didnt set the temp control to minimum but to two three clicks above that and the clicking was gone and cold air was still blowing...

i know its a ghetto fix but you can barely see it and it costs me about 30 minutes and a thick coathanger..
 
#4 · (Edited)
It's apparent that you have tinkered with the wrong thing (new actuator motor). The way these motors work is after it receives a signal for heat , the motor will operate in that direction UNTIL it senses a stop, either by the full travel of the door or by touching the white levers. Then when you request A/C the polarity to the wires is reversed, making the motor rotate in the opposite direction.

With the motor removed from the heater box, but the electrical plug still connected, the motor, when actuated, will revolve in that direction FOREVER, until you turn the key off or the battery runs down.

Therefore, the old motor and the new motor are working perfectly. If when you took apart the old motor, if neither of the white plastic gears were not cracked, then it was perfectly good. But now you have realigned the new motor to the wrong position. What made you think that the new motor was faulty?

Your ticking sound is probably being caused by one of the white actuator legs, shown in the photo below, being cracked or there is a foreign object blocking the full travel of the air door. But now you will have an additional problem with the new motor not being geared properly.
 

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#8 ·
Ok so the old motor had a cracked gear. That caused the ticking. I installed the new motor and it worked fine on the AC side it was only when I turned it to the heat side that it ran away. It is my daily driver so I had to drive it for a few days with the new motor installed before the new controls showed up. It stayed hot all the time even with full AC on. I first played with the old motor until I understood that it needs to hit the stop before it runs away. Once I had the old motor under command of the controls that is when I changed the new motor to do the same. All I really did was change the stop position manually. I am sure one should be able to set it; actually the dealer should be able to. If not there is something else causing it I just don't know what. I can reset the motor to factory setting. I have it marked on the gears. It is just the first time I encountered this with a motor control.
 
#5 · (Edited)
I hope the A/C control mechanism was not too expensive. It should not be replaced unless all of the actuators are acting dead or someone opens the unit and finds burnt circuit.

It sounds like the rail mechanism became stiff and motor is unable to move the rail in one way. Actuator motor senses the resistance and thinks that it reached the end therefor stops. When you removed the actuator, were you able to move the rail freely by hand? In fact, this might be the main reason why it is so common for these actuator to give up.

PS. please update your profile.
 
#6 ·
$30 on eBay not to bad. This motor went to the stop and no matter what you do it stays in the full hot position. It is my daily driver so I drove it with the new motor and it stayed hot no matter what, AC on full recycle the air blend motor stayed in one position. Max hot. I had trouble getting air at my feet and now with the new controls that works fine so the control was on the blink I think. Rails moved freely. Remember if I stayed within the 1/4 movement the motor worked fine. As soon as I exceed the 1/4 turn towards the hot side it runs away to max hot that is it no return. It might be the stop setting I am sure it can be set by the Dealer. It is a 98 with high miles so for now it works even though the neutral position is towards the AC side. I even checked the temp sensor pumped some hot air on it no luck the motor stayed there.
 
#11 ·
I hope someone responds although this thread is a little aged...

I have ticking sound. Took apart the glove box area and pass. airbag and got the motor out, hoping I could flip the wheel over and save the $$. No dice, the white wheel is cracked although it has a fairly good grip on the spindle (but I can see where it is not as firm as it should be, hence the slippage at higher motor speed, ie the cold part of the dial). I did flip and try but it actually made it slightly worse (faster ticking). I guess I will buy the whole motor.

Two major questions that I hope someone can set my mind to rest on.

1. I did not disconnect the air bag as i could not figure out how. Frankly I am afraid of accidentally (no pun intended) activating it by touching, pulling on or tampering with the wrong thing. I did disconnect the negative terminal of the battery before doing any of this work. Can the airbag be disconnected (ie detached from the car) and then reconnected? That sensor wire doesn't behave like your typical wiring harness. Can it be taken out and put back together?

2. Is there a correct orientation of the white lever that mates to the motor? In all the messing around the white lever came out and I don't know whether I put it back correctly. (eg full front, middle, or rear of rotation cycle?)

Again, I have the jitters about the airbag, because it can be very dangerous at close quarters and even if it's not, the cost to replace it would be way high I assume. If you can tell me a little more about this aspect it would be very much appreciated.
 
#15 ·
Here's a live shot of it. Remove the glove compartment and switch the controls from warm to cold and you will see that the operating levers do not move (they should).

You will have to remove the top portion of the instrument panel which is not very difficult. Don't let the instructions scare you. Pre-order the Blend Door Motor but when you receive it do not try to move it manually. Install it as is, part #163 820 01 08. Check with dealer for correct application.

Only order the Blend Door Motor from the dealer or an on-line dealer, as you don't want to install a faulty motor and have to do this job twice.

http://www.benzworld.org/forums/w163-m-class/1417771-diy-thread-collection-5.html#post4763314
 

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#16 ·
i'm going to be doing this procedure next weekend. Two questions, please:

1. I'm really hoping I diagnosed mine properly, since I already bought the new actuator. I accessed it (sort of) by removing the back of the glove-box. There I confirmed that the levers were not moving, but since I needed a defroster, I tried to force it to move; it wouldn't. I eventually disengaged the actuator arm from the lever by prying upward on it until it pulled out of the slot on the lever. The door then moved freely wherever I wanted it. But the arm on the actuator would still not move. Does this sound like a bad actuator? Or do I have an electrical issue TO THE actuator?

2. Somewhere on this forum, I know I saw a step-by-step on removing the top of the dash for this procedure. But now I can't find it again. Can someone point me to that?

thanks!
 
#25 ·
The only thing I could find with those color wires is for the In-Car Temp. Aspirator Blower.

The wires will have a sequence of very small numbers and letters stamped on each one. Then there will be a space and the sequence is repeated for the full length of the wire.

With a magnifying glass copy down the sequence and post back.
 

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#26 ·
The only numbers I could read off the wires is as follows. Although I cannot read some letters in front or behind.
Brown wire is -7X58/2-A (all I could read though the -A is the last letter)
Grey wire is 2632--X18/2-c-vx (I think).

This may not be very accurate as the letters were just too difficult to read.

The in temp car sensor makes sense as I just cannot get cold air out of the blowers even though I have now changed the air blend actuator. I will try and see if I can find and see if there is a blank socket as per your attached picture.
 
#30 ·
I cannot find anything else in the wiring diagrams with those color wire, but to be very honest with you, if everything is working with the radio then you shouldn't worry aout it just right now.

I'm confused as to what you are trying to say about the sampling motor. The tiny vent (green arrow) between the Double Combo. Switch should not be expelling air but it should be drawing air through the vent down the corrugated hose.

With the glove box removed, have you looked at the Blend Door Actuator to see if it moves when switching from hot to cold and vice versa?
 
#31 ·
Hello 43sqd.

Yes you are quite right. I was confused as to which way the air was moving in the corrugated tube. It does suck after all and was easy to test by placing a piece of paper on it and seeing it suck onto the inlet. So it must be working. The airblend actuator motor is working fine and moving as it should from hot to cold. I am just not getting very cold air however?

Is there a way to test the thermistor (resistor that sits behind the grill below the Hi range button)? I did get some resistance over it (0.0053ohms) but am not sure if that means much??
P.S. I appreciate all your help so far.
 
#35 ·
"I'm a new member here so please bare with me. I'm just wondering how hard it is to get to this actuator motor to be replaced?
I cannot use the AC right now because now matter how I turn the temp knob, the temp does not change.
But I can hear a ticking sound under the dash but it goes away once in awhile. Any info will be greatly appreciated..."


Hi,
Do you want to try this procedure that seems to work basically 10 out of 10 times for me? I have a '01 ML320.
Assumming you know the Compressor, fuse, relays (that run the two fans in front of the radiator) blower motor and resistor are ALL in good working conditoin and freon is charged in the system, and the issue is with the HOT air COLD air mix electric actuator (not the motor.)
1. Turn car on and while running.
2. Turn fan knob to position 0 (left dial to off.)
3. Turn the temp and air flow/Defrost knobs (middle and right) clockwise (the temp will stop at hot but keep turning the flow dial a couple of times and stop it at the same position as the temp (both knobs should end up being at the 5 o'clock postion.)
4. Simultaneously, turn both temp and flow dials counterclockwise slowly, BUT STOP THE TEMP JUST BEFORE YOU GET TO THE COLDEST/STARTING point, at the 8 o'clock postion, as opposed to 7 o'clock.) That will keep the air intake internal (as opposed to trying to open the flap to get external air inflow.)
4.1 The flow dial on right should stop at the 9 o'clock positon so air comes out of the middle vents.
5. Start the fan (left dial) but only stay in position 1 with the lowest windspeed. YOU SHOULD FEEL THE COLD AIR.
5.1 DO NOT TURN THE FAN DIAL TO POSITION 4 (MAX FAN) as this will cause (flap to close and) hot air to pump.
5.2 AFTER AT LEAST ONE MINUTE, you may turn the fan to position 2, or if necessary 3. The COLD air should continue to flow at a faster rate.
6. Again, DO NOT TURN THE FAN DIAL TO POSITION 4 and just leave the TEMP and Flow dials (middle and left) alone, and only operate the FAN (left) dial either on poistion 0, 1, 2, or 3.
If external temprature is very hot and generally durng rush hour traffic hot air does return, then please try this procedure again it should work, but generally it help when the car is running at higher speeds as the wind helps to cool down the system.
 
#39 · (Edited)
When will you guys learn that a $2 gauge attached to a can of refrigerant isn't the same as a $3,000 refrigerant charging machine. Adding refrigerant on your own could cause further problems.

You will have to explain the word "weak". Do you mean it's not cold enough or do you mean it isn't coming out of the vents strong enough?

Also, you having the new style compressor, there is no way you can tell if the compressor clutch is engaging because it is not an exterior one, but it engages internally in the compressor.
 
#40 ·
i agree with you and already have gotten quotes to evacuate and refill the system.
Before i spend the big bucks i thought i would try "toping up" the refrigerant to see if the situation improves and this is the source of my weak cooling. I would have gotten it evacuated.


weak as in the temperature of the air coming out of the vents is too high and it takes a very long time to bring the cabin to "room temperature". ( lets say 70deg F)

The air flow/volume throughput seems to be normal and the blower seems to operate normally.

Comparing the output temperature of my ml320 to the ml55 at max A/C and 10 minutes idle the ML55 is not nearly as cold at the vents. I can confirm this with my IR thermometer but i feel that will not provide with any useful data other than that its simply not as cold.

the compressor clutch is engaged and the DIY refrigerant gauge, although it might be inaccurate, did show around 45 PSI system pressure. which is around where it should be if i am not mistaken.

my next step would simply to see if the blend air motor has full range of travel. Switching to hot air works though....

can i reach the level arms/blend motor mechanism by ony taking out the glove compartent like is used to be able in my 98ml320?
 
#42 ·
Sorry to rehash an old thread, but did you ever get this working? I am having the same problem with my w163 ML55. I replaced the door actuator motor, plugged it in, and it immediately moved to the open position and stayed there, just like the old one. No matter what I do, it doesn't change from hot to cold. I am 2 seconds away from doing the old lever to mechanically open and close. I only use this ML55 to pull our horses, so I don't feel like messing with it anymore. Mercedes couldn't figure it out, they think it's the control module, but I am not willing to keep paying for diagnostics. Anyways, any help or input from someone would be helpful. Cheers
 
#46 ·
You should find a used module, Denso TN277300-0790 and see if that is the problem. If not, it is the Actuator Motor.

98 05 Mercedes ml W163 A C Control Module TN277300 0790 KM50830 | eBay

N19 is located in the middle of the Heater/AC box.

Remove both covers under the Instrument Panel and there will be an opening on both sides that gives you access to the module.

Remove the single screw holding it in place and remove it through the passenger side opening.
 

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#48 ·
Hello,

I am having similar problems with the A/C system on my 2000 ML320. The system is not leaking, and is pressurized. The compressor has been recently rebuilt. I have replaced the blend door motor, and also have plugged in a new module as described above. I have even tested the rheostat on the temp control knob, and it appears to be working fine, the ohms are consistent and it looks like it is reversing the polarity as I operate the knob.

I am at a loss at this point, if anyone has any suggestions as to a direction to go on this I am all ears.

Regards,
 
#49 ·
C>P>, it's obvious that your A/C does not work, but just telling us what you have done is only half the story. You must tell us what is not occurring.

After three mins. you have requested A/C:

1. does the clutch on the compressor spin with the pulley?

2. regarding the two aluminum pipes on the firewall, is one hot and the other cold?

3. did the A/C work properly last summer?

4. are you absolutely sure there is the proper amount of refrig.?
 

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