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82 240D, 85 300 TurboD, 94 E320, 97 E320
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17 Posts
Discussion Starter #1
OK - here's a puzzler that I could use some help to get started.

At idle, all heat controls (def, panel and foot) work fine. I also ran the flap diagnostics and all work as designed. There is plenty of A/C and heat to all vents.

Here's the twist. When it is cold and I am driving/accel, the foot air is GONE :(. Idle/decel the car and it's back - 100%:), then start driving/accel, the foot air is GONE :( and back :) and forth :(. Other flaps do not seem effected.

Seems it's a vacuum issue for sure, but where do I start? Maybe vac checkvalve?

Any/all ideas welcome - thanks, nidge
 

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E320/E250 Bluetec Ford F350 6.7l
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36,717 Posts
W210 are just reaching the age, but deteriorating vacuum elements are common issue on W124.
My theory is that one of your element diaphragm is leaking a bit and while idle is giving plenty of vacuum, the open throttle is not, so the system goes to default what is defrost mode. Those things are pretty hard to deal with because of access. I made pretty long topic about W124, what might help a bit, but start with hooking up vacuum gauge to the system to confirm my theory.
 

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Banned
1999 E300 TD
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2,045 Posts
I regretfully have a much more localized potential reason for the issue.

My problem is that I am not at the shop to confirm. However, till Monday can you answer the following questions:

Does the same event happen with both heat and air?

When you accelerate where does the air get directed too?

While at idle can you redirect the flow without an issue?

While accelerating are you able to successfully redirect the air flow and more specifically to the foot well?

What is the result of the AC fault test? Any faults?

Good luck!!
 

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82 240D, 85 300 TurboD, 94 E320, 97 E320
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17 Posts
Discussion Starter #4
Thanks Kaijtek1 - yes, lines are getting fragile. I was looking for a start point for troubleshooting. Your comment that defrost mode is default is an indicator - that's where the air goes. I will start by visually checking lines and connectors and listening for leaks.

Plutoe - here are some answers;

Does the same event happen with both heat and air? Right now we are in winter in Michigan. It started when I noticed my feet stay cold. I will say, that I did not notice this "switching" when the air was in use this summer. I can audibly hear the redirection of air. It seems to fade and operate decently once the cabin warms. So, I would say mainly when the car is calling for 100% heat mode.

When you accelerate where does the air get directed too? defrost

While at idle can you redirect the flow without an issue? yes

While accelerating are you able to successfully redirect the air flow and more specifically to the foot well? no, when it's not working, it's not working in manual and auto

What is the result of the AC fault test? Any faults? yes, b1422 - K1 Connection

Thanks again, nidge
 

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Registered
E320/E250 Bluetec Ford F350 6.7l
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36,717 Posts
Thanks Kaijtek1 - yes, lines are getting fragile. I was looking for a start point for troubleshooting. Your comment that defrost mode is default is an indicator - that's where the air goes. I will start by visually checking lines and connectors and listening for leaks.
Small vacuum leak in element deep down under the dashboard is not detectable by listening. What you can do is using MityVac as a vacuum pump, make a tee with gauge and hook up the elements tubing to it for testing.
The bad news is, that if one diaphragm deteriorated badly, the other are not far behind.
The diaphragms alone are hard to buy, while elements cost in the range $30-60 and there is about 8 of them.
On W124 rebuilding the system took a member 2 days.
Good luck.
 

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Banned
1999 E300 TD
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2,045 Posts
Thanks Kaijtek1 - yes, lines are getting fragile. I was looking for a start point for troubleshooting. Your comment that defrost mode is default is an indicator - that's where the air goes. I will start by visually checking lines and connectors and listening for leaks.

Plutoe - here are some answers;

Does the same event happen with both heat and air? Right now we are in winter in Michigan. It started when I noticed my feet stay cold. I will say, that I did not notice this "switching" when the air was in use this summer. I can audibly hear the redirection of air. It seems to fade and operate decently once the cabin warms. So, I would say mainly when the car is calling for 100% heat mode.

When you accelerate where does the air get directed too? defrost

While at idle can you redirect the flow without an issue? yes

While accelerating are you able to successfully redirect the air flow and more specifically to the foot well? no, when it's not working, it's not working in manual and auto

What is the result of the AC fault test? Any faults? yes, b1422 - K1 Connection

Thanks again, nidge
Just to confirm---at idle you can successfully push the button and redirect the air without an issue, however while acceleration the push button will NOT work and redirect the air to any direction. IF THAT IS CORRECT, you do not have a vacuum issue

An issue like yours is always attributed to a so called unknown vacuum leak and very difficult to diagnose my email. The parts are cheap, but the labor to install the parts is very high.

However if you have the tools and persistence to confirm if you have a leak, remove the glove box and you will see a block(switch over block) with loads of colored vacuum lines---find the one incoming line, connect a hand held vacuum generator and pull 300 mbar if it drops by 30mbar after one minute, you in fact do have a leak.

Good luck. These issues are hard to diagnose over the phone!!
 

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82 240D, 85 300 TurboD, 94 E320, 97 E320
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17 Posts
Discussion Starter #7
OK - it's been a while, but I finally got around to diagnosing. I got a MiteyVac for Christmas and took out the glovebox. Where the heck is the vacuum distribution box (Y11)? I just can't see it. I started to tear apart eh dash, but wisely stopped to ask.

Thanks
 

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1997 E 420, 155K Miles, Stock
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17 Posts
Status of Troubleshooting?

Any updates on your troubleshooting? I think I have the same problem as you. Any feedback would be greatly appreciated,


OK - it's been a while, but I finally got around to diagnosing. I got a MiteyVac for Christmas and took out the glovebox. Where the heck is the vacuum distribution box (Y11)? I just can't see it. I started to tear apart eh dash, but wisely stopped to ask.

Thanks
 
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