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  #1  
Old 05-11-2006, 06:21 PM
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A/C intermittent problem with the air flow

Hi all,

I have a SL320 from 1998.

The problem is related with the A/C. Sometimes, the air flow decrease (the power), but I don't touch any button of the console (and it's not on AUTO mode). After a few minutes or seconds, the air flow increases automatically, to the correct flow power... I don't know why is the reason... probably the filter is dirty... I don't know!!!!!

It happens when the car stops or when the car starts to run. It must be due to the movement of the car, when taking a curve or something thus.

The problem is not related with the AUTO button. I put the power of the air flow to the MAX position, but sometimes the flow changes (decrease) for 5 or 10 seconds, between low speed and high speed. It is like something is covering the tube... may be a leaf???????

Could help me somebody?

Thank you very much in advance.
Regards,
Jorge Ruano

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  #2  
Old 05-11-2006, 08:41 PM
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Jorge, next time this happens lightly wiggle you ignition key left/right and see if the fan starts running again. If yes, it may be time to replace the ignition. if no - well at least we ruled this out
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  #3  
Old 05-12-2006, 04:40 AM
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Hi,

I think the motor is OK, because the fan is working (non stop until I press the button to turn off). Probably are the valves.

Today I've observed that when I press the air re-cycling button, sometimes nothing happens and sometimes the airflow is greater. Do you think that the valves are involved in the air re-cycle circuit? Or, may be the air filter?

I think that the air filter is only for the external air, and when the air re-cyling button is pressed, the air doesn't pass for the air filter... isn't it?

Where are the valves and where are the air filter? Can I clean the valves and/or the air filter? Is it easy to do?

Thank you in advance and regards,
Jorge Ruano
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  #4  
Old 05-14-2006, 12:21 PM
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Maybe I am way off base here, but my 92 500 SL changes air flow volume in A/C/Automatic Mode every time I accedlerate hard. I think, hope, , it is normal. Under hard acceleration the system appears to drop the compressor and lower air flow. As soon as I let up to cruise, all operation returns to normal. Under light acceleration, no change occurs.

Lea,
Any comments?
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  #5  
Old 05-14-2006, 02:05 PM
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Not noticed it myself, but my euro '93 has no auto mode so maybe that's why?!
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  #6  
Old 05-18-2006, 03:27 PM
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I have more information about the problem:

When I ignite the engine and I turn on the A/C I put the maximum power of the flow (I touch the button for the flow speed to the maximum). The A/C works fine, with the maximum speed of the flow... but after 5 or 10 minutes, the speed of the air flow decreases, I don't touch any button, I don't touch nothing .

The A/C decreases the speed automatically after a few minutes but I don't know the reason. After it, I can't increase the speed of the flow to the maximum power. The display of the flow power marks the maximum power, but It isn't true, because it decreases, but the display marks the maximum power... why????

Thank you in advance.
Regards
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  #7  
Old 05-19-2006, 03:26 AM
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Location: Northumberland, UK
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This is your evaporator temperature sensor. It has failed.

What happens is this. The evaporator temp sensor fails; the evaporator ices up; after about 5 or 10 mins it stops working; the cabin heats up; the acc system tries to compensate by increasing the fan speed; eventually the fan is running full speed but no air is coming out.

You can check this yourself by running the diagnostic test from the push button control module. The evap temp sensor is value number 5, it should be about 4 or 5 deg C, if it has failed it will return an illogical value such as 40 deg C. If you use the search facility you will find a raft of posts (many by me) on this topic. Search for "evaporator temperature sensor" in Tech Help and SL Forum.

It is a cheap part (cost me GBP40, probably <$100), and an easy fix (pull the old one out, put the new on in).

Here are some relevant threads (I've done the search for you):

1999 SL 500 Blower Issue - Help Please!
R129 AC problem
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  #8  
Old 05-19-2006, 05:31 AM
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Thank you for your help!!!

I'll try to pull the evap sensor out and buy a new one (do you know the MB reference of the evap sensor?).

I will inform you about the news.

Regards,
Jorge
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  #9  
Old 05-19-2006, 05:56 AM
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The only part number I have is from the invoice. I am not 100% certain it is correct (because I had a lot of other work done), but pretty sure it is:

Service operation: 83 8054 01 Temperature sensor on evaporator replace
Part number: A 210 830 07 72 Temperature sensor

It actually cost GBP25.00.

Good luck! And run the diagnostic test to make sure.

And please post the results here for future readers who have the same problem.
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  #10  
Old 05-20-2006, 12:05 PM
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Exclamation

Hi again,

I have taken the mesasurements of my A/C in test mode. The parameters are the following:

01 - 34 ºC
02 - 32 ºC
03 - 36 ºC
05 - 36 ºC
06 - 87 ºC
07 - 14'3
08 - 42 ºC
09 - 13 ºC
10 - 080
20 - 00
21 - 000
22 - 000
23 - 000
24 - 12.0
40 - 02
41 - 03
42 - 03
43 - 6 - C
50 - 35 ºC
51 - 22 ºC
52 - 13 ºC
54 - OFF
60 - CLO
61 - 4.1
62 - 3.7
63 - 4.1
64 - 3.8
65 - 0.9
66 - 1.4
The temp of the cluster indicator was 27.5 ºC

The first parameters were increasing from low values to the final maximun values that I have written (until they have become stabilized in those values).

Do you think that the evaporator temp sensor fail??

In Spain the evaporator temp sensor (Part number: A 210 830 07 72 Temperature sensor) costs 47.00€.

Thank you in advance.
Regards,
Jorge
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  #11  
Old 05-22-2006, 04:09 AM
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Yes, I am sure it has failed. The evaporator temperature sensor reading is 05; when fully functioning it should return a value of 4deg C or so. The reading you have, 36 deg C is consistent with failure: it is ambient temperature plus a bit extra, probably from heat soak from the engine.

Here is a diagram showing the component location:

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  #12  
Old 06-01-2006, 07:15 AM
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I have changed the evaporator temperature sensor (Part number: A 210 830 07 72 Temperature sensor). The new measurement for the number 05 value is less than 7ºC.

But... in the A/C display, I put the low tempoerature ("LO") for the most cold, and I put the maximun air flow, for the most power, and the A/C works better with the new sensor, but it continues failing because it continues cutting the air flow, more time in cutting it takes but it finishes it cutting. Before, it fails in 4 or 5 minutes, and now, it fails in 15 o 20 min. Works better, but...

I observe that now, when I press the re-cycling air button, the air flow works with the maximum power, and it works fine, but only if I pressed the re-cyling air button.

I don't know what can I do and what will be failing now... or if it is the normal operation of the A/C in R129.

Some idea?????
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  #13  
Old 06-01-2006, 08:40 AM
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Dear Brothers,

I have exactly the same problem as you mentioned. It starts 2 weeks ago when I discover that no much air is blowing out from the vent. It cures when I press the re-circulating button. Then last week when the A/C did not start at all when the car is running. It goes back to normal when I hit the re-circulating button again, I guess. Today, it rains heavily and the A/C suddenly stopped working after 10 mins. running. However, the A/C becomes normal again after I switch off and restart the car.

I will read the post you mentioned and see if I can fix it.

So hot in Hong Kong!!
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  #14  
Old 06-01-2006, 09:43 AM
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Where is the evaporator temp. sensor located on a 79 450SL

Jim
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  #15  
Old 06-05-2006, 04:33 AM
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Quote:
Originally Posted by jruanoru
...it continues failing because it continues cutting the air flow, more time in cutting it takes but it finishes it cutting. Before, it fails in 4 or 5 minutes, and now, it fails in 15 o 20 min. Works better, but...

I observe that now, when I press the re-cycling air button, the air flow works with the maximum power, and it works fine, but only if I pressed the re-cyling air button.
Hmmm. Is the fan still running (albeit without airflow)? Does the display indicate that the fan is still running?

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