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Old 02-08-2007, 05:08 PM
Registered User
Join Date: Aug 2006
Location: Houston, TX
Posts: 450
Question A/C diagnosis requested

Finally needed real levels of A/C here in Houston today. Rebuilt CC unit in place. No trouble codes logged.

Start car, temp dials set to 75 both sides, no recirculation. Fan comes on like gangbusters and then slowly tapers off to "idle" over 2 or 3 minutes.

Ran the diagnosis to log the values from the various sensors after driving the car for about 30 minutes and got these values:
1 - 81 (in car temp at aspirator)
2 - 82 (outside temp)
3 - 42 (left heater core temp)
4 - 41 (right heater core temp)
5 - 43 (evaporator temp)
6 - 09 (ECT sensor - I think this actually converts to 109)
7 - 13 (Ref pressure in BAR)
8 - 60 (Blower control signal) - the dial was set at MAX - as I dialed it down to MIN, the value dropped to 8
9 - 03 (Indicates Kammerer control unit)
16 - 0 (no activated charcoal filter)

Here's my analysis of the #'s
1 & 2 look about right - it felt about 80 inside the car, and that was the temp around the car when I got out - temp gauge below odometer read 78.
3, 4 & 5 also look correct, given that I had set the A/C to LO on both dials, which should guarantee max cooling - so no water should be flowing to the heater cores
6 - I don't even know what an ECT sensor is, so I have no idea here. AllData is VERY cryptic about this sensor.
7 - maybe OK based on outside temps, but I didn't take the time to look this up.
8 - proper signal is being sent to blower motor
9 & 16 - who cares.

To repeat, DTC trouble codes - NONE.

I'm thinking blower control module (if that's the right term?). No matter where I set the fan speed dial, it just gives minimal airflow. Maybe the sucker is overheating when the high fan speed is called for at startup and never recovers.

I'd also guess that possibly a sensor is feeding bad data to the CC unit, but even if it thought it was too hot or too cold somewhere, I should be able to override the fan speed with the dial, right?

All suggestions are welcome.

Also, I have a small mouse caught in my blower - it goes squeek, squeek, squeek on low - is there something I can lubricate or am I looking at a new motor soon?

Thanks in advance!

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Old 02-08-2007, 06:54 PM
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Uh.... Would it be too much to ask the year and model. Is it safe to assume that it is a Mercedes Benz?
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Old 02-08-2007, 08:20 PM
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Join Date: Aug 2006
Location: Houston, TX
Posts: 450

All that typing and left out the best part . . . .

'92 300SE
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Old 02-08-2007, 10:17 PM
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Join Date: Oct 2005
Posts: 4,263
ECT is engine coolant temperature.
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Old 02-09-2007, 12:21 AM
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Join Date: Aug 2006
Location: Houston, TX
Posts: 450
Thanks for the explanation about the ECT. 109 is too high a #, based on the temp gauge, which was probably about 85.

Still don't think the ECT has anything to do with it. However, it might explain why the CC comes on for heat when you first start the car in cold weather. I would have expected it to have no fan speed at all until the motor was warm enough to provide heat. However, you get heat with low fan speed until the temp gauge starts to move, at which time it switches to high(er) speeds. Having cold breezes on your feet isn't the most comfortable of feelings. I had assumed that the behavior was by design.

Any other ideas about the fan?
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Old 02-09-2007, 12:40 AM
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Join Date: Jan 2002
Location: NY
Posts: 500
If all other temperatures are in degrees F, it would be 209F. I'd suggest switch to deg C. for this test.
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Old 02-12-2007, 09:52 AM
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Join Date: Aug 2006
Location: Houston, TX
Posts: 450

Still hoping for some help here. Last suggestion of changing to C wasn't useful - the test results don't change based on whether you're reporting in C or F.

One thing I noticed is that I've got complete fan control when the car is in heating mode. Go to A/C and the no fan control problem starts.

Any suggestions? I'd hate to have to take this to the shop when it's likely something we can diagnose and I can fix myself.

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Old 02-12-2007, 01:53 PM
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Join Date: Jan 2002
Location: NY
Posts: 500
I did not suggest the test result would change. The possible usefulness is in the correct interpretation of the results.
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Old 02-12-2007, 05:40 PM
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Join Date: Aug 2006
Location: Houston, TX
Posts: 450
I'll check and see what the difference is.

According to AllData, the values returned for the ECT sensor will be two digits, and that 04F should be interpreted as 104F. They make no mention as to whether a 2 as the first digit is even a possibility. If this sensor is engine coolant, 104F seems highly unlikely as the temp gauge was showing about 90c (194F) at the time.

I'll have a look to see what answers I get when switching the display to degrees C.
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Old 02-13-2007, 01:35 PM
david s poole
Join Date: Mar 2005
Location: dallas
Posts: 1,822
sounds to me as though the blower motor regulator is faulty.from your description you could also have worn out bearings in the blower motor.what! you say it's only 15 yrs old [should still be under warranty ha.ha.]
David S Poole
European Performance
Dallas, TX

"Fortune favors the prepared mind"
1987 Mercedes Benz 420SEL
1988 Mercedes Benz 300TE (With new evaporator)
2000 Mercedes Benz C280
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Old 02-13-2007, 02:48 PM
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Join Date: Aug 2006
Location: Houston, TX
Posts: 450
Thanks, David. Kinda what I thought too, since all the "players" in this game are either new, or newly rebuilt. It is curious that I have complete fan control in heating mode and only have trouble with the cooling mode.

Are the bearings serviceable in the fan - I've read some posts where folks have used transmission fluid in small quantities to silence a squeaky bearing.

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