HVAC system has a mind of its own - Mercedes-Benz Forum
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post #1 of 23 (permalink) Old 08-01-2019, 02:02 PM Thread Starter
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HVAC system has a mind of its own

On my '97 E420 the AC runs, and it even blows cold! Mostly.

It seems to get confused though. And it seems that no matter which buttons I push, and regardless of whether it is in automatic or manual mode, the air coming out of the vents has little to no relation to the setting on the control panel. The exception is that the fan speed controller works as expected.

The most amusing part is how the right and center right dash vents are blowing cold air while the left and center left vents are blowing hot air.

Either:
a) There is some aspect of this sophisticated, elegantly designed, German engineered HVAC system that I am missing.
b) Something paranormal is occurring.
c) Something broke.

The forum's insights would be appreciated. Cheers.
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post #2 of 23 (permalink) Old 08-01-2019, 02:15 PM
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Item c.

Most likely your duovalve (heater core control ) on the left side.

But you should obtain the fault codes per


You should also get the sensor values

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post #3 of 23 (permalink) Old 08-01-2019, 03:16 PM Thread Starter
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Alrighty then. I nipped out to the parking lot and ran the codes. These came back:

B1234 - Sun sensor
B1235 - Emissions sensor
B1419 - Electromagnetic clutch

I ran the erase procedure and all three codes cleared. I'll see what the AC does on the drive home tonight.
Thanks.
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post #4 of 23 (permalink) Old 08-01-2019, 03:48 PM Thread Starter
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I also ran the sensor values:

1 in car temp: 46
2 outside temp: 33
3 left heater core temp: 33
4 right heater core temp: 33
5 evaporator temp sensor: 27
6 ECD sensor: 38
7 refrigerant pressure: 06
8 refrigerant temp sensor: 30
10 blower control voltage: 1.3
11 emission sensor voltage: 4.7
12 sun sensor voltage: 2.6
20 aux fan control: 0.0
21 engine speed: 00
22 vehicle speed: 00
23 terminal 58D %age: 00
24 battery voltage: 11.4
40 software status: 71
41 hardware status: 34

I'm reading the refrigerant pressure as 0.6 bars, correct? This seems low.
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post #5 of 23 (permalink) Old 08-01-2019, 04:05 PM
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No, it is 6 bars. No decimals in values.

6 bars is fine when the engine is not running.


Run the engine and a/c with temp values set to LO and LO, and obtain the readings immediately after the a/c starts (compressor engaged), and keep the engine running for 5 minutes to stabilize at idle. and then obtain the values again.

Also check the codes again to see if any of them comes back (especially the 419 one)
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post #6 of 23 (permalink) Old 08-01-2019, 06:13 PM
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B1419 would indicate your clutch fuse blow up and that thing is not replaceable.
Observe if the clutch is turning with AC activated.
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post #7 of 23 (permalink) Old 08-02-2019, 10:51 AM Thread Starter
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The AC ran normally last night and this morning. I didn't recheck the codes. I figure if the air is blowing nice and cold, the electromagnetic clutch is working.
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post #8 of 23 (permalink) Old 08-02-2019, 10:56 AM
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When it does not, check the diagnostic codes again. B1419 does not always mean that the clutch is kaput. It may simply mean that the controller has a bad electrical connection with the compressor clutch coil which may be intermittent.
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post #9 of 23 (permalink) Old 08-02-2019, 03:22 PM
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Quote:
Originally Posted by Verbal View Post
The AC ran normally last night and this morning. I didn't recheck the codes. I figure if the air is blowing nice and cold, the electromagnetic clutch is working.
This morning was cold in Seattle, so the air was cold without AC.
Do you really have that many troubles to stick your head under the hood?
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post #10 of 23 (permalink) Old 08-02-2019, 04:06 PM Thread Starter
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Quote:
Originally Posted by Kajtek1 View Post
This morning was cold in Seattle, so the air was cold without AC.
Do you really have that many troubles to stick your head under the hood?
Ha ha! No, I was just lazy.
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