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Only hot air from vents no cool outside air

29K views 90 replies 16 participants last post by  43sqd 
#1 · (Edited)
1998 ML320 Only hot air from vents no cool outside air

1998 ML320
With A/C off or on I am getting hot air out of the vents and even when I trying to vent in outside air w/ AC off nothing but hot air from vents. Any DIY ideas I can try to fix this problem? Thnx.
 
#2 · (Edited)
Did a search and found this post/reply

Go into archives, many people have same problem, very common, DETANE did a video of how to replace it by removing glove box, you have access to replace from there about a 2 hour job, dealer will tell you that you need to remove dash, bullshit for more money, dealer can do it in probably 30 min or less. If you dont know how to go to archives, go to search this forum on top, type in air blend actuator, go to posts, Good luck

My question is my '98 has the turn controls/cable, no motor. Could this be the issue?

Added Information:
1. Compressor and clutch are turning and not cycling on/off
2. When I turn the temp dial to red the vents will blow hot air, but back to blue not cold air.
3. #44 Fuse is good.
 
#3 ·
Did a search and found this post/reply

Go into archives, many people have same problem, very common, DETANE did a video of how to replace it by removing glove box, you have access to replace from there about a 2 hour job, dealer will tell you that you need to remove dash, bullshit for more money, dealer can do it in probably 30 min or less. If you dont know how to go to archives, go to search this forum on top, type in air blend actuator, go to posts, Good luck

My question is my '98 has the turn controls/cable, no motor. Could this be the issue?

Added Information:
1. Compressor and clutch are turning and not cycling on/off
2. When I turn the temp dial to red the vents will blow hot air, but back to blue not cold air.
3. #44 Fuse is good.
Im confused, are both the compressor and clutch working? Are you saying that even though its <40F outside (im guessing) you're still getting hot air coming through the vents if its on the blue?

When I had my ML and lived in Syracuse, I'd have to drive sometimes with it right in the middle temp dial because it would heat up so much that full blast was unbearable.
 
#14 · (Edited)
Yes most of the year the temp dial is all the way blue, I think the last time I used the heat was back in 3/10. Problem started when we had a cold night a couple weeks ago and I dialed it to red.
Not here something I've noticed is that when I put it back to blue (cold) heat comes out but over time let's say a day I will get cold air again, strange... So if i get this I have to remove the top of dash as well as the front? No way to access the motor by just taking of the front dash? Also how do you get the woodgrain panel off the front radio/temp cluster this is where I'm stuck at getting the front dash off, sure hate to break or crack it.

Again thanks for all the help here.
 
#6 ·
i'm not a fan of the '60s (the decade that is :p ) but i would say that if it is mid 60s (f) you should get mid 60s f air blowing from your vent when the temp control knob is at cold and the ac is off.

does sound like your blend door may be the issue. did you check to see if the air gets warmer as the vehicle warms up? that would be a strong indication.
assuming you cleaned out your pollen filter, imho your next step is to start taking things apart to see if your flaps are behaving as they should.

be warned however: when i checked my air blend motor i found the stories of easy access were vastly exaggerated. i ended up having to take the top of the dash out to get to the screws holding the blend motor. also i made a mess of the passenger air bag cover (it now sits high).

never did find a problem (my feet were freezing from december onwards! so i just removed all the plastic in the driver foot wells so lots of air comes out - not relevant to your problem but maybe of interest to someone else with cold feet)
 
#8 ·
Yes as the ML warms up the air does get hotter. Is there an instruction on getting the dash out? I've come to a point were I have all the screws out but can't seem to get the dash off. How can you test/tell if the blend door is not working. I am a novice at this so going thru the glove box seems easier but I already have the dash 1/2 way off. Thanks
 
#7 ·
I had the same problem 2 years back in my 2000 ML55. I had to take the dash off and replace the blend motor and there was also another part. Took me like 5 hours with bunch of ziploc bags and I took pictures of what goes where. I would have posted but my computer had crashed, so lost all the pictures. But now everything is OK. I just had to add 1 can of R134 last year after so many years.
 
#9 ·
Any suggestions. Air conditioner was working fine till I turned the dial to red (hot) this morning, again hot air is coming out with a/c on. This happened last week but a/c eventually came on.
Still looking for dash dismantle instructions to get to the bend door motor. I have gotten all the way to where I can not pull the dash off, stuck at the center by radio cluster. Thnx.
 
#10 · (Edited)
In post #5 I asked you to explain the circumstances, but you did not answer.

Here are the instructions for removal. It is only necessary to remove the upper portion to replace the Blend Door Motor. There are two screws securing the top section of the radio cluster and two at the bottom. For the bottom ones you have to pull away the lower section to see them.
 

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#13 ·
for dash removal the process is simple - work away from 'the inside outward' (radio hole) and the 'outside inwards' (a column interior panels and plastic kick plates...etc) keep removing stuff and looking for hidden fasteners and prying with the wedge till you get off what you need to.

one more thing:

re: "With A/C off or on I am getting gusts of hot air out of the vents and even when I trying to vent in outside air w/ AC off nothing but hot air from vents. Any DIY ideas I can try to fix this problem"

besides the air blend motor another source of problems might be that you have a left over politician hiding inside your dash. did this problem start right after the mid-term elections?? :big laugh:
 
#17 ·
Ticking noise usually comes from A/C box actuators. In your case, most likely blend air motor. 43sqd provided the key documents to you for this weekend project.

Take some pictures during the project and post it here please. This will (a) help you to remember things when installing parts back and (b) other members on this forum to do this in the future.
 
#22 · (Edited)
When we bought the ML earlier this year, the infamous 'tic tic' was intermittent. Recently became constant, and the loss of AC became constant along with the sound.

While Detane's video looked appealing to use in replacing the air blend motor, I disliked the cutaway of the airbag door. Thanks to 43sqd for posting an alternative method with detailed instructions for pulling the top dash. Did it today, took just under 3 hours - including chasing the family cat when it escaped. (I am not the fastest wrench in the east, and my 40 yrd sprint ain't what it used to be!).

Out of the ordinary tools used:
- T15 socket for the side screws hidden by the doors
- Clear silicone to restore the weatherstripping
- Bondo plastic filler blade used for wedging out parts

Tips:
1) Used plastic bags marked with location as suggested earlier in the thread. Very useful technique when I reinstalled the instrument cluster and had 2 screws left over. Would not have known where they went if discovered at the end of the job!
2) Did not completely remove the dash - just pulled it forward enough to get my arm in to access the air blend motor.
3) Kept the battery connected - and did a post installation test to verify the new blend motor worked before reinstalling the dash.
4) There are 8mm screws on either side of the dash, need to use a T15 torx to remove the lower plastic (hole visible in lower grey panel next to black ratchet in photo), pull bottom dash forward after removing glove box and instrument cluster, then the 8 mm screw become visable. (Just about all the other screws were 7mm hex head, except for the 2 phillips screws holding down the air blend motor.)

Of course the truck looked like it was vandalized just prior to pulling the upper dash. Some photos:
 

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#23 · (Edited)
Here is a photo of the upper dash pulled up and forward. Loosen the sides first, there is a metal lip under the airbag motor that needs to be overcome. The center vent makes for a good handhold to pull up. Takes a few forceful tugs to get things going - tight fit towards the windshield. No need to pull it completely out, just reach in from the passenger side and look through the windshield while removing and replacing the motor. (Full disclosure - I have long arms to make the reach)
 

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#24 · (Edited)
This photo shows location of the air blend motor. (Photo is through the windshield, hence the reflection of my garage) My truck is a 1998 ML 320.

Airbag is upper left in photo - blend motor has red electric tab in back, air blend levers are white.

When I looked at the internals of the old motor, the large plastic gear used to actuate the external slide lever arm was cracked. 13 years, and it finally gave away. Hope the new one lasts as long.

Many thanks to 43sqd for the alternative instructions!! :bowdown:
 

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#27 ·
Al,

See post 48, pdf file for Radio R&I, complements of 43sqd.

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

My ML radio was JVC, which was a breeze to pull out. For my other 2 MB, I have keys from ebay (under $5) to release the locks. You can probably get keys at Radio Shack if you can't wait for mail order. Kinda tricky to get the latches the first time. Pretend you are a safe cracker trying to feel the tumblers click! :D

Mike
 
#29 · (Edited)
So, I did this arduous task (half way anyway) today. I followed 43sqd's directions but missed the green screws as they aren't on the front of the area as they appear in the pic but actually up behind where the stereo was. Directly beneath a large horizontal trunk of wires. The heads are 7mm and face down (screw tips point up). I tried to "tug" the dash off with removing these and got the HVAC main trunk ducting jammed between the firewall and the large tubular steel piece that runs horizontally through the space behind the dash. Couldn't budge it. Ended up have to hydraulically jack the dash back down with a jig I rigged up and the help of my wife (bless her heart).

Anyway, once I got it back down it freed up and I removed it by lifting up and barely getting by the cruise stalk and then handing it out the passenger door to my lovely bride. Once It was out, all the foam around the HVAC was a wreck, have to replace.

I tried just flipping the dash over like ATM but it failed miserably. Not saying he is wrong just BE CAREFUL and take out every screw before you try to remove.

One note, one I replaced the air mix motor and powered it up, it moved the lever all the way to the hot air and stayed there. Adjusting the temp by turning temp knob to blue had no effect. I am hoppng this is a sensor issue and will rectify itself once I put it all back together tomorrow. We'll see.
 
#30 ·
JWSMITH - I think you should read the first half of this thread before you put everything back together. It discusses the actuator end limits. If something is not clear then suggest you ask as it would be a real shame for you to have to do it all again.

http://www.benzworld.org/forums/w163-m-class/1495807-ml320-blend-air-motor-controls.html

I have no personal experience of this job - I just remember reading this thread when I was trying to work out why, after removing a broken lever on my defroster actuator, the actuator seemed not to know its end limits anymore.
 
#33 ·
re

"I have no personal experience of this job - I just remember reading this thread when I was trying to work out why, after removing a broken lever on my defroster actuator, the actuator seemed not to know its end limits anymore"

So hot to teach them again their positions ? i changed my flap actuator and not is opening-working only wone way nothing changes when i set differest temp.
 
#35 ·
You are missing one gear altogether in your opened actuator. There is a vacant metal shaft where it is supposed to sit. Once that gear is installed it will turn the orange gear (mounted on top of a potentiometer, aka variable resistor). And that potentiometer provides position feedback to the controller N19.
 
#38 · (Edited)
Witek_M,

I think the MBZ troubleshooting documentation is very poor on this one. The potentiometer in the actuator M16/8 and the in-cabin NTC S97/6 are in series and that resistance is evaluated by the controller N19 in a simple analog feedback loop. This decides where the actuator moves. If there is an open and resistance between pin 2 and pin 12 (N19 disconnected) is not in range the actuator will keep spinning in an attempt to reach its set-point. And I can see where that cracks the larger gear.

The first test needs to be to check resistance between pin 2 and pin 19. It needs to be between 1.7 kOhm (25C) and ~4kOhm. Then manipulate the little red gear since the actuator is cracked open and observe the resistance value changing. At one extreme the value needs to be identical to the resistance of the sensor (1.7 kOhm @25C) and at the other closer to 4 kOhm.

Further notice the path between pin 2 and pin 12 is only complete if S98 is plugged in. Else the blue wire from pin 2 of the N19 connector floats in air.

Ingo
 
#40 ·
Mateusz,

can you clarify whether the temperature in the cabin is -5 degree C? That would be really cold.... If that is really the case the resistance would be between 7.1kOhm and 9.3kOhm depending on where the blend door actuator servo is in its range of travel. Your value of 16.4 kOhm is not possible at all. Either the servo variable resistor or the in-cabin sensor or the cabling are bad. Test the in-cabin sensor. Then test the variable servo resistor in the actuator. Adding both together gives the series resistance that is seen by N19. Plausible values at moderate temperatures are between 1.5 kOhm to 4 kOhm.

I have created a small PDF to illustrate how the HVAC blend door actuator works and where to measure. The little red gear in the actuator is attached to the variable resistor. The control module N19 tries to maintain a certain series resistance (measured between pin 2 and pin 12). Once the sensor in the cabin changes its resistance the series resistance changes and that makes the motor move until the value is back to the target value.

Make sure that the control module N19 is not connected when you check resistance. If it stays connected the values can be erratic.

Ingo
 

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