1996 e320: A/C warm at high speed and cold at idle - Mercedes-Benz Forum
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post #1 of 25 (permalink) Old 06-15-2019, 01:06 PM Thread Starter
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1996 e320: A/C warm at high speed and cold at idle

I purchased this car from a man who had it stored for many years. He stated that the A/C had been working intermittently when he parked it and that his mechanic had informed him it was a sensor. Now that I have the vehicle, I took it to my mechanic who evacuated/recharged it. At that point it was cooling well.

Here is what is now happening: It cools very well at idle and slow speed. At highway speed it seems to warm and/or cool intermittently. Once I get to a stop light, it goes ice cold again.

Any ideas? I have searched the forum but did not find anything like this.

I appreciate any help.
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post #2 of 25 (permalink) Old 06-15-2019, 01:19 PM
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You need to get sensor readout using AAC panel. Sounds like sticky heater duo valve letting some hot coolant trough at high engine speeds.

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post #3 of 25 (permalink) Old 06-15-2019, 01:22 PM
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Did the a/c work fine at highway speeds after the mechanic re-charged it and how long ago was it ?


You can get the sensor readings using the instructions below and post them.

STAR TekInfo

start from item 2.

Post the sensor number versus the reading for all readings (1 to 43).

Also obtain the possible fault codes using the menu below.

STAR TekInfo

starting from item 3
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post #4 of 25 (permalink) Old 06-15-2019, 01:24 PM Thread Starter
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It has only been a week since I got it recharged. I think it has been happening all along, but today was the first day where it was extremely obvious.
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post #5 of 25 (permalink) Old 06-15-2019, 01:28 PM
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Could be an overcharge issue. That is why you need to monitor the pressure sensor readings when at highway speeds.

Press the REST button till the menu comes up, then press the left AUTO button till the left side reads 7. Right side will change from low teens to upper teens depending on the cooling demand and speed. Have a look at the changes in the pressure values as you cruise along.
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post #6 of 25 (permalink) Old 06-15-2019, 05:55 PM Thread Starter
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When I started the car and idled it was between 15 and 16. As I began to drive, it lower, one number at a time, down to 8. Stayed at 8 until I pulled into my driveway. As soon as I started slowing down, the number climbed back up. By the time I was parked in my driveway, it was back to 15.
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post #7 of 25 (permalink) Old 06-15-2019, 06:26 PM
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If your mechanic recharged the refrigerant by pressure readings rather than by weight, it may have improper amount of refrigerant in it. From empty to full, the system requires about 1 kg of R134a (which amounts to a bit less than 3 12-ounce cans.

I would take it back to the mechanic to confirm proper charge.

Also perform readings per post #3.
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post #8 of 25 (permalink) Old 06-16-2019, 12:14 PM Thread Starter
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post #9 of 25 (permalink) Old 06-16-2019, 12:21 PM
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Now you need to do same readout at speed.

1972 280SEL 4.5
1999 ML320
2000 E320
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post #10 of 25 (permalink) Old 06-16-2019, 12:23 PM Thread Starter
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engine RPM as if I where driving or actually on the road?
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