I've done some searching so before the moderators get all over my back for repeating this problem, I haven't found the solution after hours of searching. Anyhow, here goes:
2001 S500. It blows cold air out of the center vents. The driver side vent seems to be a mixture of hot/cold and the passenger and rear is all hot. The AC dial is set to automatic on the dash. Also, the refrigerant level is fine.
Through searching these forums and speaking with the Head Mechanic at MB of Buffalo, here are the two probable causes:
1. Duovalve - Either a plunger is stuck or part of the unit was bad.
Outcome: I disassembled, cleaned, then rebuilt. When i reassembled I tore the heads off of 2 of the 5 torx screws. Therefore, I had to buy a new duovalve. So now I have an entirely new new duovalve-assembly and the problem still exists. The problem is not the duovalve, at least I do not think (see below).
2. Climate control unit in console
Outcome: I bought a used unit from ebay. Hooked it up and it didn't have any affect - it worked like the old unit. Sure, the used unit could be defective too but the chances are unlikely. By chance, a 2001 S430 came in for service so I "borrowed" it for testing. The outcome once again was the same. For satisfaction, I hooked both my old and new climate control modules up in the S430 and the AC functioned completely normal. The problem is not the climate control unit.
Final note: I do not have the million-dollar MB scanner but our scanner does show that one of the duovalve coils has full voltage while the other has 0. This definitely sounds like the problem, but based on a new duovalve assembly it sounds like it might be more of a symptom. Does anyone have any ideas? I am not a mechanic but just a proud MB owner trying to better understand what the problem is and save some dollars (not off to a good start!)
Anyhow, any input would be very appreciated. Thank you for reading my post.
I got the same problem a few months ago. Full freon but only cold air from center vents & the rest of the vents in the car hot. I thought it was duovalves problem too but after 4 visits to the dealer, they finally found that the cabin temperature sensor was bad. They replaced it & everything was fine.
I always heard that the hot/cold problem was related to monovalves or duovalves (duo in this car).
This problem has been around for ages and this valve always seems to be the culprit. I remember changing a monovalve in my 1986 300SDL when I had the same problem..
I would suggest you look at the wiring to and from the duovalve, and make sure the thing is working correctly. I have heard of broken connectors and wiring causing problems like yours. I'm sure you can find the proper pinouts somewhere on the web, then use them to test the voltages at the duovalve to make sure it's being told to do the right thing.
By the way, I need a climate control unit for my 2001 S430 (the unit below the COMAND unit in the dash.. it's the one with all the buttons on it such as AUTO and REST). If you want to sell your spare cheap, let me know
Last edited by bhatt : 08-25-2008 at 12:42 PM.
Reason: Corrected last sentence.
I've done some searching so before the moderators get all over my back for repeating this problem, I haven't found the solution after hours of searching. Anyhow, here goes:
2001 S500. It blows cold air out of the center vents. The driver side vent seems to be a mixture of hot/cold and the passenger and rear is all hot. The AC dial is set to automatic on the dash. Also, the refrigerant level is fine.
Through searching these forums and speaking with the Head Mechanic at MB of Buffalo, here are the two probable causes:
1. Duovalve - Either a plunger is stuck or part of the unit was bad.
Outcome: I disassembled, cleaned, then rebuilt. When i reassembled I tore the heads off of 2 of the 5 torx screws. Therefore, I had to buy a new duovalve. So now I have an entirely new new duovalve-assembly and the problem still exists. The problem is not the duovalve, at least I do not think (see below).
2. Climate control unit in console
Outcome: I bought a used unit from ebay. Hooked it up and it didn't have any affect - it worked like the old unit. Sure, the used unit could be defective too but the chances are unlikely. By chance, a 2001 S430 came in for service so I "borrowed" it for testing. The outcome once again was the same. For satisfaction, I hooked both my old and new climate control modules up in the S430 and the AC functioned completely normal. The problem is not the climate control unit.
Final note: I do not have the million-dollar MB scanner but our scanner does show that one of the duovalve coils has full voltage while the other has 0. This definitely sounds like the problem, but based on a new duovalve assembly it sounds like it might be more of a symptom. Does anyone have any ideas? I am not a mechanic but just a proud MB owner trying to better understand what the problem is and save some dollars (not off to a good start!)
Anyhow, any input would be very appreciated. Thank you for reading my post.
As far as car age is concerned ...go for the duo valve 90%
connect a voltmeter to the duovalve coil.. If it reads 12 volts DC the wiring is ok.. When there is 12 volts to the coil the valve is sposed to be closed.. If hot water is still passing thru then there is something sticking the plunger.. another way is to use a pinch off clamp on the water hose leaving the valve.. if the vents cool off then it is definitly the duovalve..
I'am having the exact same problem on my 96 S-320 with a slight twist. If the temp is set above about 69/70, I get the hot air out of side vents. I have to lower the temp to low, then ease up to about 69 and it is then cold on side vents. Where is this duo thing located on the car, I would like to make the tests you speak of. Thanks in advance for any suggestions.
hi m8 had exactly the same problem on a 2000 s320 of my dads cleaned the duo valves and that didnt work re-gassed the a/c system all works perfectly now hope that helps.
I would assume if you have COLD air coming from ANY vent, Refrig. is NOT the likely problem, It's deflection(to side vents) problem, no?? Also the in-cabin seneor should be ok If you are getting cold air anywhere/any vent..
I think the dealer blew some smoke up you about the in-cabin sensor. Think about this, how would the sensor be able to determine WHERE the cold or hot air is coming from, it just samples the average cabin temp, no??? I think most service centers tell you what is convient and believable for the symptom. They may have just connected up a wire, then billed you for the other, sounds better for them.
I never fixed b/c summer went away, not that Winter is here the opposite problem.
Hi everyone and thank you for the feedback. I started this string and being new to the forums I thought I would get a response with an email notification but I guess that was optional. All the while there are these great replies. Anyhow, I didn't do anything to fix the problem yet because we got into fall and kept the windows and roof open.
Now that the cooler weather is hear and I want to use the heater, it seems like there is the opposite problem - now I get cold air blowing out some vents and the hot air in others. I am relatively sure it is not the duovalve assembly, although it could be a wiring problem. I will definitely check out the voltages next time I get an opportunity.
So, now that we KNOW its not the duovalve or interior control module, any other suggestions as to what the problem is (other than the wiring prob)?
- The interior temp sensor... Where is that located? can it be tested? How? If it is in the interior control module, I know this isn't the problem as I purchased a brand new unit from MB and it had no effect. I needed it anyhow, the original had two dead lines in the display of the unit.
Linear Mode
