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post #1 of 28 (permalink) Old 06-14-2007, 07:21 PM Thread Starter
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AC Freeze up?

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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post #2 of 28 (permalink) Old 06-14-2007, 10:39 PM
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Quote:
Originally Posted by DonA
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.
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post #3 of 28 (permalink) Old 06-15-2007, 05:17 AM
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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
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post #4 of 28 (permalink) Old 06-15-2007, 06:16 AM Thread Starter
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Quote:
Originally Posted by Diesel Benz
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.

Quote:
Originally Posted by Diesel Benz
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.

Quote:
Originally Posted by Diesel Benz
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
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post #5 of 28 (permalink) Old 07-02-2007, 02:20 PM
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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
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post #6 of 28 (permalink) Old 07-02-2007, 02:30 PM
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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.
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post #7 of 28 (permalink) Old 07-03-2007, 03:09 PM
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Typcial Freeze up causes:

-Low refrigerant (R-12, R134a etc)
-Failed expansion valve
-Mis-positioned expansion valve bulb (depending on type of valve design)
-Moisture in system (contaminated desicant)

DB
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post #8 of 28 (permalink) Old 07-23-2007, 02:02 PM
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Quote:
Originally Posted by DonA
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
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post #9 of 28 (permalink) Old 07-27-2007, 03:11 PM
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In my case it was the blower regulator. Refrigerant level OK. Fixed, under warranty.

Kevin
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post #10 of 28 (permalink) Old 08-06-2007, 02:16 PM
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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.

Hugh
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