A/C Won't Blow Cold - Mercedes Benz SLK Forum

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#1 Old 3 Weeks Ago
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Question A/C Won't Blow Cold

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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Until an expert responds, remember to use our search feature

here are my forum search results with key words
r170 ac does not blow cold

https://www.google.com/search?source...4dUDCAc&uact=5
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Also, have a look at the duo valve threads.
Easy job to try before other possibilities.
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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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Originally Posted by naviathan View Post
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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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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Originally Posted by naviathan View Post
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.

--------------

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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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
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Originally Posted by jbanks15 View Post
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
Well I dunno about these new-fangled R171's 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
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@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-z...ew?usp=sharing

HVAC Component interlink: https://drive.google.com/file/d/1wM2...ew?usp=sharing
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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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Hi,

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

HTH, Cheers Dave
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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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Originally Posted by naviathan View Post
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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Originally Posted by naviathan View Post
The air coming out of the vents is ambient temp.
That probably means that the duos are working and are doing the best that they can .. time to get it scanned.
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Quote:
Originally Posted by naviathan View Post
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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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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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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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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Replies to others or your own thread count as posts as well, just keep that in mind.
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