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AC Freeze up?

18K views 27 replies 16 participants last post by  ot1 
#1 ·
On my wife's 2006-E320CDI and after driving about 40 minutes in humid ambient weather the AC system seemed to 'freeze up'. All controls on Auto, Temp set a 72F, car interior began to warm up. Air flow seemed low out registers, though fan speed sound was normal. Air flow continued to drop, though it did not stop. Manually raising fan speed produced little, if any, additional register flow, though fan sound increased. Turned A/C switch off for about 10-15 minutes and register air flow slowly increased to near normal. Turned manual A/C switch back on by going to full Auto and all cooling returned to normal.

Service center seemed to ignore wifes comments re. above (practiced with her and she had it down). They found a blower regulator control fault and replaced the blower regulator. Don't know the source of this but re-discussing with them got some go-round that I would have gotten massive water out registers if my scenario was valid. Don't believe that is the case as there is a demister on outlet that should catch entrained water droplets.

Finally got them to agree to recheck with another service call by letting system run on lot for 30-40 minutes. Did find out that 33F minimum is controlled by probe not refrigerant pressure level as American cars used to use to control.....Comments? Will take back in for check in a few weeks.......
 
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#2 ·
DonA said:
On my wife's 2006-E320CDI and after driving about 40 minutes in humid ambient weather the AC system seemed to 'freeze up'. All controls on Auto, Temp set a 72F, car interior began to warm up. Air flow seemed low out registers, though fan speed sound was normal. Air flow continued to drop, though it did not stop. Manually raising fan speed produced little, if any, additional register flow, though fan sound increased. Turned A/C switch off for about 10-15 minutes and register air flow slowly increased to near normal. Turned manual A/C switch back on by going to full Auto and all cooling returned to normal.

Service center seemed to ignore wifes comments re. above (practiced with her and she had it down). They found a blower regulator control fault and replaced the blower regulator. Don't know the source of this but re-discussing with them got some go-round that I would have gotten massive water out registers if my scenario was valid. Don't believe that is the case as there is a demister on outlet that should catch entrained water droplets.

Finally got them to agree to recheck with another service call by letting system run on lot for 30-40 minutes. Did find out that 33F minimum is controlled by probe not refrigerant pressure level as American cars used to use to control.....Comments? Will take back in for check in a few weeks.......
I had a blower regulator failure on a W210. It started gradually and intermittently stopped blowing. Finally it got short-circuited and started blowing at full power. You however state that the blower fan sound was normal at the point it stopped blowing. Do you mean it was normal when set to max manually, the fan noise increased along with the fan speed setting? If the fan sound indicated the fan motor properly reacting to the speed setting, it does not sound like the regulator issue (even if that has been a common issue at least for W210).

If it wasn't the regulator, then it sounds like it could be the evaporator temperature sensor (no idea if they often fail, never hear of that). But this should leave an error code and in any case should be easy to read the temperature with diagnostics tools when the car is running.

I agree that there should not be any water leak problem if the evaporator got frozen, normal operation creates a lot of condensed water that but in this case it would have frozen. The fact that switching AC off momentarily helped recovering the air flow also seems to support the idea of evaporator freezing.

If the evaporator sensor is failing, the problem should be there still after the fan regulator change. Ask them to read diagnostics codes and read the sensor values when the car is running with AC on.

Finally, this control system on American cars, how can it only work on refrigerant pressure, my understanding is that all cars must have a sensor or a switch at the evaporator or behind it (a sensor or just a bi-metal temp switch). Older European systems simply controlled the compressor clutch with this temp sensor, modern compressors run continuously.
 
#3 ·
I had it happen as well on a road trip. Humid conditions (patchy fog) temperature was around 70F.

Has not happened since. When you go in for servicing, have them check the system for low freon (R-134a).

With a freeze up no codes will be set since everything was working properly...Sort of.

I would have to check to see how the freon valve/regulator assembly regulates the freon. If it's an expansion type this could have a temp sensor too far from the evaporator. If its a fixed orifice type then this would point to low freon, since these use VDP type compressors I suspect the latter as the culprit.

DB
 
#4 ·
Diesel Benz said:
Do you mean it was normal when set to max manually, the fan noise increased along with the fan speed setting? If the fan sound indicated the fan motor properly reacting to the speed setting, it does not sound like the regulator issue (even if that has been a common issue at least for W210).
Yes, the fan speed sound was consistent with the speed setting; higher=higher, lower=lower. However, the air flow was low until 'defrosting' of the core took place; or at least thats what I believe happened.

Diesel Benz said:
If it wasn't the regulator, then it sounds like it could be the evaporator temperature sensor (no idea if they often fail, never hear of that). But this should leave an error code and in any case should be easy to read the temperature with diagnostics tools when the car is running.
Would the sensor still leave an error code even if it was 'thinking' wrong? I would try to check on the air registers but they may be 'blended' air, not what is coming from the core.

Diesel Benz said:
Finally, this control system on American cars, how can it only work on refrigerant pressure, my understanding is that all cars must have a sensor or a switch at the evaporator or behind it (a sensor or just a bi-metal temp switch). Older European systems simply controlled the compressor clutch with this temp sensor, modern compressors run continuously.
Don't know about newer cars but 10-15 years ago freon pressure set the minimum temp in some American cars. Ergo low freon pressure = low evaporator temp.

Thanks for the reply/s. Problem did occur with rainy weather at ca. 74F outside on a short trip. May have to wait through the summer in central Texas before another good test
 
#5 ·
Just had my car serviced, the system was .3lbs low. Dealer evacuated the system and performed a systems check including the pressure sensors. Refilled and the system is now 4 degrees cooler.

Because of the heat this time of year there is no way to know for sure if the system will freeze up at 70F with high humidity.

The system check was done free of charge under warranty.

DB
 
#6 ·
Freeze up is usually caused by low freon which means there is a leak in the system. Don't know about the blower regulator but low freon if it is in fact a freeze up is the first thing to look at. If it goes real low the compressor will not engage as there is a low pressure switch. As far as moisture coming from the vents ... unlikely even with low freon. Sorry, not Freon but I believe that its R134 that is used. I had a BMW years ago that suffered from this and eventually a factory kit of some sort was installed to prevent freeze up. BMW's in my estimation still suffer from poor A/C units.
 
#8 ·
DonA said:
On my wife's 2006-E320CDI and after driving about 40 minutes in humid ambient weather the AC system seemed to 'freeze up'. All controls on Auto, Temp set a 72F, car interior began to warm up. Air flow seemed low out registers, though fan speed sound was normal. Air flow continued to drop, though it did not stop. Manually raising fan speed produced little, if any, additional register flow, though fan sound increased. Turned A/C switch off for about 10-15 minutes and register air flow slowly increased to near normal. Turned manual A/C switch back on by going to full Auto and all cooling returned to normal.

Service center seemed to ignore wifes comments re. above (practiced with her and she had it down). They found a blower regulator control fault and replaced the blower regulator. Don't know the source of this but re-discussing with them got some go-round that I would have gotten massive water out registers if my scenario was valid. Don't believe that is the case as there is a demister on outlet that should catch entrained water droplets.

Finally got them to agree to recheck with another service call by letting system run on lot for 30-40 minutes. Did find out that 33F minimum is controlled by probe not refrigerant pressure level as American cars used to use to control.....Comments? Will take back in for check in a few weeks.......
I had the identical problem on a road trip earlier this month! Same blower behavior. Upstate NY, expressway, warm day (it's always humid out here). Turning AC off resulted in brief but unsuccessful respite. We got off the expressway and after some time with AC off, on local slow roads, we turned the ac back on and the blower and AC were back to normal. Later on the same trip a very brief recurrence on the highway - which self-corrected.

Glad to see this post and your resolution (more refrigerant) in a later post as I am in for the 12.5k service tomorrow.

The manual does say that if the system stops working it is likely low on refrigerant. This seemed at odds with the behavior exhibited but perhaps that is it. I will let you know my experience at MB service.

Kevin
 
#10 ·
Happened to me for the first time on a road trip last week. Same thing (turning off the compressor for a while) brought the airflow back to life.
 
#26 ·
Replaced evaporator temperature sensor to stop freeze-up



For the benefit of current readers of this thread, my unit would freeze up after sustained high-speed driving on the freeway - the clue is that the airflow drops off significantly.

I replaced the evaporator temp sensor from under the dash, which is an easy job, the part is not expensive, and problem is solved.


That was 3 years ago, and it still works fine.
 
#13 ·
My 2008 Bluetech (E320) keeps freezing up on long trips in high temp/humidity areas. Twice dealer has checked, says no problem but I note there is never any water dripping from the evaporator. Dealer claims water drips onto a drip pan and it will not be seen. This sounds fishy to me. Anybody have similar experience?
 
#14 ·
My 2008 Bluetech (E320) keeps freezing up on long trips in high temp/humidity areas.
“May” be humidity sensor (part 2118300572) Mercedes Benz Workshop Manuals > E 320 4MATIC Wagon (211.282) V6-3.2L (112.954) (2003) > Heating and Air Conditioning > Sensors and Switches - HVAC > Humidity Sensor > Component Information > Description and Operation > Page 18448 in addition, they should verify that AC system is fully charged by evacuating and re-filling the system to the correct level.
 
#16 ·
Dew point sensor

The problem is most likely the dew point sensor that is missing in some model cars. I had this same problem on my 2006 and after researching, found that some years did not have the dew point sensor installed. The part number is 2118300572
The sensor needs to be installed into the empty connection inside the compartment where the cabin filter is located. It is on the right side of the opening when you take off the cabin filter.

Also, see this service bulletin

DTB P-B-83.00/102 MAY07 (Service Bulletin)
reduced air flow/ cooling from climate system after long drives
 
#17 ·
Here is what my service manager said about the problem. " The condensers on those vehicles will ice up on long trips. He recommended that on longer trips cycle the ac button off for about 5-10 min every hour. That should give it time to de-ice. " He also said the humidity sensor is just a 500ohm resistor.

Isn't technology great!

John :D
 
#18 ·
We have had several full tank runs of close to 400 miles in our E500 with the AC on the whole time in the southern states and never had any issues. I think the MB dealer there is dosging it because he can't fix it. Especially if it was Bergstrom. Their service department is a fiasco.
 
#20 ·
You said your service manager and you listed your location as Green Bay in your profile. I know all of the dealers in the state and I assumed it was Bergstrom.
Either way there are ways to fix the problem. It has happened to this model and other makes and models.
 
#22 ·
It is out of warranty. Stay away from Bergstrom. Next time you are in the metro Milwaukee area you could call MB of Elmbrook/International Motors or Concours as they are much more familiar with the these cars than a Fox Valley based dealer. MB of Elmbrook/International Motors will give you a free loaner. Concours is not that nice.
 
#24 ·
2012 S550--exact same issue

AC freezes up in the same manner as described in this thread. Have been to the dealer 3 times in the last 6 months and the problem has not been resolved. The last time they replaced the blower motor. The first two times they did nothing. Lines continue to freeze. What should the freon pressure be when the temp is 80?
 
#25 · (Edited)
I didn't want to start a new thread just to describe my 'A/C Freeze-up' so thought I'd resurrect this one instead. My troubles started Friday when I noticed what I believed to be a coolant smell coming from engine compartment at start-up. Engine also briefly made a strange whirring noise that quickly went away before I could pop the hood & isolate it's origin. I drove on highway for approximately 20 miles, intermittently catching a whiff of 'coolant' smell while in stop & go in busy city highway traffic so decided to stop at rest area to listen to engine & see if odor was still noticeable or any obvious leaks were presenting. The engine while idling had developed a new sound, a rhythmic thump that I'd never heard before. I opened hood & quickly determined new sound was coming from V-belt. The culprit turned out to be A/C compressor & sound was being generated by it's pulley travelling in & out of alignment of v-belt's circuit. Miraculously, v-belt was still keeping this pulley spinning in play & able to keep it from wandering completely off track but I knew it could go at any second so I gingerly eased back onto highway & set course with new urgency for workshop. I was certain I was going to throw v-belt any second & lose all functionality requiring a tow but again miraculously car made it to mechanic approximately 10 miles after discovery of issue. I demonstrated concern to tech before cutting off car's engine. The pulley popped right out of front of compressor with slightest nudge of a crowbar. V-belt was the only thing keeping it in place apparently. Long story short, $1.5K later... a new OEM compressor, v-belt, drier, 950g of R-134a/46 PAG oil & car again has ice-cold AC that will set you free so I guess I feel lucky as car didn't leave me stranded on roadside needing a tow. Odometer is just about to roll over to 239k miles & I believe this was it's original compressor so all things considered not a bad service life & it performed admirably right up to the end. "Coolant' smell was apparently PAG oil/R134a as it trickled out during operation, vaporizing from heat of engine. Summer heat has outdoor air temps pushing 100F almost everyday lately so AC pretty much mandatory unless driving at night exclusively. I ordered a digital A/C control unit from ebay for $75 to replace my analog one that is still working fine & will soon be retired as a spare. I had to replace my blower fan's voltage regulator back in January of this year so have been down that road as well. I replaced that component with a salvage yard unit. Here's a picture of new control unit's #'s, just arrived in mail today:
next I'll do a write-up of it's install & integration into vehicle's hive mind.
 
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