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Registered 1999 SLK230
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98 Posts
Discussion Starter #1
This one has me a bit confused. The clutch works, the pump runs, but I get no cold air. I feel like the system might be low on freon, but the pump is running and I thought the pressure switch would kill it if it was low. None of the lines coming from the pump get cold at all. I'm hoping there's something I'm missing here that you guys will pin down for me.
 

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Administrator 2009 SLK 55 AMG/Founding Member 2006
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99,797 Posts

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Registered 1999 SLK230
Joined
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98 Posts
Discussion Starter #4
I tried the duo valve and there is a click when I pull the plug on it and put it back on. Feels like it's working, but just because it activates doesn't mean it's closing I guess.
 

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Premium Member 2001 SLK200K/2001 SLK320
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2,279 Posts
I tried the duo valve and there is a click when I pull the plug on it and put it back on. Feels like it's working, but just because it activates doesn't mean it's closing I guess.
It would be unusual for them both not to work but it's not unheard of, fuse 15 can be the culprit but as you say there is an audible click then maybe that can be ruled out and either the shafts are broken or they are both sticking.
One pipe in, two pipes out, general rule of thumb is that the two out pipes are significantly cooler than the in pipe when the system is calling for cooler air (because it is the duos job to regulate the hot coolant flow). Start car from cold and immediately ask for cold on the dial wheels on the controller, let the engine warm up on tickover and see what the pipes do.
 

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Registered 1999 SLK230
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98 Posts
Discussion Starter #6
Even when the car is cold, the air temp is not, so I'm inclined to think it's not the duo valve.



Is it possible that the ambient temp on the gauge cluster not reading could have something to do with it? It's stuck at -38 or something like that. One of the threads in that search mentioned by @jbanks15 said something about it possibly causing problems with the a/c as well as the fuel mileage.
 

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Premium Member 2001 SLK200K/2001 SLK320
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2,279 Posts
Even when the car is cold, the air temp is not, so I'm inclined to think it's not the duo valve.



Is it possible that the ambient temp on the gauge cluster not reading could have something to do with it? It's stuck at -38 or something like that. One of the threads in that search mentioned by @jbanks15 said something about it possibly causing problems with the a/c as well as the fuel mileage.

From my own experience(s) ..

When I had a broken external air temperature sensor on my (admittedly non-A/C) 200 - see thread HERE - it made not one jot of difference to the heating system and I ran it without that sensor for a couple of years or more. The only thing that that sensor appeared to do was to tell me what temperature the external air temp was at.

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I had non-working duos on my 320 so I've been there as well ..

You fail to say how non-cold your cabin air actually is, can you define that? i.e. Ambient, Warm, Hot?

If the A/C is not working and the duos are, you will still get ambient air temp at the vents - just like switching the A/C off

If the A/C is working but the duos are not, you will get air IRO 48°C

During my small quest to sort my own duos out, I did manage to ascertain that there's 4-5 possible causes for non-working duos:
1. Duos are kaput
2. Broken wire to duos
3. Fuse 15 is blown
4. HVAC Controller is FUBAR
5. Faulty Internal Air Temp Sensor

HTH
 

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Administrator 2009 SLK 55 AMG/Founding Member 2006
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99,797 Posts
when my outside temp gauge broke on previous 2005 SLK 350, the tech told me, for what it was worth, it did have an affect on the fuel mixture because of it reading high. true or not, who knows :D
 

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Premium Member 2001 SLK200K/2001 SLK320
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2,279 Posts
when my outside temp gauge broke on previous 2005 SLK 350, the tech told me, for what it was worth, it did have an affect on the fuel mixture because of it reading high. true or not, who knows :D
Well I dunno about these new-fangled R171's :D But for what those sensors cost - IRO $15 - it makes sense to have one .. in my case it was a question of when I got a round tuit but it really didn't seem to have any adverse affect on the car whatsoever, it was more of an annoyance that it constantly read -38 rather than anything else that eventually forced me to put a new one in >:D
 

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Premium Member 2005 SLK350
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2,423 Posts
@naviathan

I hope this is helpful. The first link below lists all the fault codes your HVAC system can generate. As you will note, the first item listed is a fault for the abient air temp. Using an appropriate diagnosis system - the best is the MB HHT/DAS/Star system, will help point you in the right direction. Throwing parts at it without a complete diagnosis will just drain your bank account.

The second link is a detail of each HVAC component and the interactions betwen them. In most cases, if any component is not functioning the system is not functioning. If you would like any of the additional referenced documents just let me know. Good luck.

HVAC fault codes: https://drive.google.com/file/d/1Y-zNAc-vhzbQBvNAT14XgkD0FuICDAxO/view?usp=sharing

HVAC Component interlink: https://drive.google.com/file/d/1wM2Uowg36UrwTGZuWDYWoA4psCDGbw9P/view?usp=sharing
 

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Registered 2012 SLK55 AMG w/P30
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3,581 Posts
Feel the temperature of the fittings leaving the compressor. If the compressor is working correctly, one of the fittings (the high-pressure side) should be significantly hotter than the other. I do not recall if the 170 uses a variable bypass compressor. If you say there is a clutch on it, then it does not. If it uses a variable bypass, then the above test would not be conclusive.
 

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Premium Member 2002 R170 SLK V8 5.0
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3,539 Posts
Hi,

Post Facelift is not Variable Bypass, so I doubt Pre Facelift is either ................

HTH, Cheers Dave
 
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Registered 1999 SLK230
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98 Posts
Discussion Starter #13
The air coming out of the vents is ambient temp.


Where would be the best place to acquire an appropriate piece of diagnostic equipment? Does this work through the OBD-II port like a domestic vehicle?


One of the fittings on the compressor was getting hot. The opposing fitting didn't feel cold though.
 

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Premium Member 2005 SLK350
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2,423 Posts
The air coming out of the vents is ambient temp.


Where would be the best place to acquire an appropriate piece of diagnostic equipment? Does this work through the OBD-II port like a domestic vehicle?


One of the fittings on the compressor was getting hot. The opposing fitting didn't feel cold though.
In order to Private Message other members you must have at least 15 posts. You are currently shy of that. To get to that level quickly go to the new member introduction section and welcome enough to get your count above 15. Then reach out by PM to member @i860 and tell him what you are interested in. He should be give you some direction.
 

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Registered 2012 SLK55 AMG w/P30
Joined
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3,581 Posts
The air coming out of the vents is ambient temp.


Where would be the best place to acquire an appropriate piece of diagnostic equipment? Does this work through the OBD-II port like a domestic vehicle?


One of the fittings on the compressor was getting hot. The opposing fitting didn't feel cold though.
One side should be hot. The other side does not have to be cold. Sounds like the compressor is running correctly.
 

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18 Posts
At least in my family's older benz's the AC will try to blow cold even if it is low on gas, if everything seems to work, but there is no cold then a refill might fix the issue, it's usually pretty cheap as well, we do it routinely every so often.
 

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Registered
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23 Posts
Have you reset the ac ... I had this issue and pressed the ec and rest buttons together until the lights flashed for about a minute ... turned the car off then on again Abd hey presto cold air again ... I had to do this after regassing as well
 

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Registered 2007 SLK55 AMG
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54 Posts
Is the A/C button turned on when the car is started? Not sure if it is all SLK’s, but mine will not blow cold if the A/C button is engaged when the car is started unless the button is turned off and back on again.
 
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