Aux Fans and A/C Issues - PeachParts Mercedes-Benz Forum

EricSilver · #1 05-09-2018, 01:29 AM

Car: 2001 E430

I force-started my aux fans by holding both AUTO buttons down for 30 - 33 seconds, with the engine running. Then I displayed Climate Control status codes (by holding REST button for approx 10 seconds):

01 = In-car temp sensor
02 = outside temp sensor
03 = left heat exchanger temp sensor
04 = right heat exchanger sensor
05 = evaporator temp sensor
06 = coolant temp
07 = refrig. pressure in bar
]08 = refrig temp sensor
09 = nothing
10 = Blower control voltage
11 = emissions sensor (B31)
12 = sun sensor
20 = aux fan control

I read online that the values for aux fan control (20) should be 6.1 to 10. This was a single source so I will not assume it was authoritative.

My values were:
Fans on Full: 21.1
Fans Off: 3.2
Fans low speed: Did not check.

Is this evidence that not only are my fans failing, but perhaps the control module as well? (The 3.2 value concerns me, and perhaps explains why the fans don't start without a push, except when force-started with high voltage.

Additionally, with the fans at full, refrigerant pressure reading (07) showed 20 and did not budge. With fans off, it fluctuated from 05 to about 11 when underway; and into the mid-teens when stopped (outside temp 70 degrees). I am obviously low on refrigerant, despite a pressure gauge reading of 40-43 psi.

Diseasel300 · #2 05-09-2018, 11:15 AM

You should never have to push-start a fan. If it's that tight, you have a failing bearing or brush/commutator problems.

I also wouldn't rush to judgement on the refrigerant level either. On a cold day (70˚F is pretty cold for A/C diagnosis), your head pressure will be way down. Wait for a 90˚+ day before touching the charge, it may be fine.

EricSilver · #3 05-09-2018, 11:31 AM

Great. I will go ahead and plan on replacing the left motor, or perhaps the whole unit.

This weekend will be in the 90's here, so I will check the refrig pressure again then.

Thanks for the good feedback.

Quote:

Originally Posted by Diseasel300

You should never have to push-start a fan. If it's that tight, you have a failing bearing or brush/commutator problems.

I also wouldn't rush to judgement on the refrigerant level either. On a cold day (70˚F is pretty cold for A/C diagnosis), your head pressure will be way down. Wait for a 90˚+ day before touching the charge, it may be fine.

Diseasel300 · #4 05-09-2018, 12:29 PM

Disconnect the belt and spin the driven motor. If it sounds rough, seems tight, the fan freewheels for a long time, or the bearings make a clicking/clanking sound as it spins, plan on replacing the bearings at a minimum. Good bearings will be smooth and quiet. They'll also have a very slight drag to them due to the grease inside.

EricSilver · #5 05-09-2018, 01:51 PM

Spinning by hand, with the belt on, both fans will rotate freely, for a couple of seconds. At most, I hear a faint squeak on the driven one -- but when I first heard it last week, it was very loud, the way my idler pulley sounded about a week before it self-destructed.

I am going to assume, with the 3.2 (volts??) shown in the diagnostics, it should move freely, so rust or corrosion or dry grease or messed-up brushes/commutator is making that impossible, without giving it a push by hand.

I did not know the motor could be serviced. I will try that but will still buy a replacement, since I suspect I will need it

Quote:

Originally Posted by Diseasel300

Disconnect the belt and spin the driven motor. If it sounds rough, seems tight, the fan freewheels for a long time, or the bearings make a clicking/clanking sound as it spins, plan on replacing the bearings at a minimum. Good bearings will be smooth and quiet. They'll also have a very slight drag to them due to the grease inside.

Diseasel300 · #6 05-09-2018, 02:19 PM

Bearing noise = toast. Not sure about the W210 fans if they can be serviced or not. I know the 126 can be serviced by drilling out a couple of rivets. My fan ran, but howled like a banshee. New bearings shut it right up and been fine ever since. 3.2V may or may not be enough power to break the motor free, assuming it actually is providing 3.2V. I guess you'll find out with the new fan.

EricSilver · #7 05-09-2018, 10:58 PM

It reminds me of an old electric train set I have. Over the years, more and more current is required to move the locomotive, presumably because of dust and dried-out lubrication in the motor.

I did observe something interesting:

Since the first 90-degree days last week, the A/C would oscillate from cold to warm, with refrigerant pressure ranging from 06 to 28, and evaporator temps from 46 to 84 -- coldest/highest pressure intervals when stopped at traffic lights (engine ~600 rpm) and warmest/lowest pressure intervals on highway ( engine 2,000 rpm+) The cold air was never constant; it always oscillated.

Today that changed. While waiting to meet a client I idled for about 15 minutes and the car stayed comfortably cool the whole time, with no warm/cold oscillation. Evaporator temps varied between 49 and 55 and refrigerant pressure fluctuated from the high to mid teens. Aux fan readout showed voltage fluctuating from 10 to 21, and they were indeed spinning.

Standing at the driver door looking at the CCU, I could hear the fans spin faster or slower as displayed voltage rose and fell. There was a delay of about five seconds between a voltage display and the corresponding change in fan speed.

After some reflection I realized that instead of running the A/C on Auto as I usually do, I had manually set the blower fan to max. When I reduced the blower speed three levels, fan voltage dropped to 3.2 and fans stopped spinning (visually checked). After increasing blower speed to max, voltage rose to 21 but the fans did not move -- until after I toggled the EC off (red light on, fan voltage 3.2) and then back on (red light off, fan voltage 21), after which fans resumed spinning, the compressor engaged, and the constant cooling resumed.

This behavior suggests a connection to the blower motor regulator but I have never hard of such a thing, nor does it seem to make sense. I cannot, however, ignore what I observed.

Quote:

Originally Posted by Diseasel300

Bearing noise = toast. Not sure about the W210 fans if they can be serviced or not. I know the 126 can be serviced by drilling out a couple of rivets. My fan ran, but howled like a banshee. New bearings shut it right up and been fine ever since. 3.2V may or may not be enough power to break the motor free, assuming it actually is providing 3.2V. I guess you'll find out with the new fan.

Diseasel300 · #8 05-09-2018, 11:35 PM

If the fans aren't running, the head pressure climbs to the point it trips the high pressure cutout when you're idling. That's likely why you were getting the oscillating temps when the fans didn't run.

Not sure how you're getting 21V to the fan when you're running a 12V system. Perhaps the values given are PWM steps and not volts.

The only way to really tell what's going on is to probe the voltage going to the fan motor with a voltmeter and see what's actually happening. If you have voltage at the motor, but it isn't spinning, you know the motor is the problem.

If you see the CCU has the fan set wide open but you have no voltage at the fan motor, you know the problem is in the communication line or the fan motor controller.

All the CCU readout is telling you is what it thinks its doing, not what's actually happening. If you have an open connection somewhere or the motor controller is bad, the numbers on the display are meaningless.

EricSilver · #9 05-09-2018, 11:46 PM

I am changing oil tomorrow so voltage probe is my next step.

So far, the CCU readout has reflected what is happening with fans, refrigerant pressure, and evap temp, albeit with a delay of a few seconds. Evidence leans more towards a faulty fan but I would not be surprised if it is the controller.

Quote:

Originally Posted by Diseasel300

If the fans aren't running, the head pressure climbs to the point it trips the high pressure cutout when you're idling. That's likely why you were getting the oscillating temps when the fans didn't run.

Not sure how you're getting 21V to the fan when you're running a 12V system. Perhaps the values given are PWM steps and not volts.

The only way to really tell what's going on is to probe the voltage going to the fan motor with a voltmeter and see what's actually happening. If you have voltage at the motor, but it isn't spinning, you know the motor is the problem.

If you see the CCU has the fan set wide open but you have no voltage at the fan motor, you know the problem is in the communication line or the fan motor controller.

All the CCU readout is telling you is what it thinks its doing, not what's actually happening. If you have an open connection somewhere or the motor controller is bad, the numbers on the display are meaningless.

EricSilver · #10 05-10-2018, 10:13 PM

There is definitely power at the fan plugs. Readings on the meter increase/decrease with observed engine speeds, and CCU readings -- with one exception:

At the 21.1 level, the voltage at the meter can spike high, or go low. At levels below 21.1, the metered voltage matches the display.

Sounds like something else is responsible for this errant (21.1) signal.

EricSilver · #11 05-18-2018, 01:18 AM

UPDATE
Installed a new fan (just the left w/motor) and that issue is resolved. The swap was easy, fast and surprise-free.

The new fan is by Vemo; smooth and silent. The old fan felt "lumpy" when rotated by hand, as if like-pole magnets were moving over each other offering resistance to motion in any direction. That is the only way I can describe it.

The new fan responded to the voltages reflected n the CCU, turning on briefly on engine start and then for longer duration when coolant temp reached 215 degrees and/or refrigerant pressure reached 14 bar.

That said, I still am having A/C cooling issues, but as the ambient temp was only in the 60's last night, when I installed the fan, I could not really test it.

Also, because I am still getting the anomalous values for the (20) Aux Fan control Status Code -- and because, when force-started via the CCU, they spin at an insane speed and made a sound I never again want to hear, I am suspecting the fan control module may also need attention.

Diseasel300 · #12 05-18-2018, 10:44 AM

Certainly sounds like that fan motor was singing its last hurrah. Not being familiar with the 210 Climate control, I can't help you further in troubleshooting the CCU/fan module issue. It could be one or the other, or something unrelated entirely, who knows! I try to avoid computerized controls as much as possible, they're such a pain to troubleshoot when something goes wrong.

As far as the A/C performance is concerned, wait for a hot day (85˚+) and check the charge pressures. Make sure when you're checking, you have all 4 windows down, blower on high, temp set low as it'll go.

I know some "supertech" will come along and flame me for even suggesting it, but a decent "rule of thumb" pressure chart against ambient temps will get you close:

Note that the pressures given in that chart assume the car is idling without any additional airflow over the condenser from a separate fan. It also assumes maximum load on the system.

If your high side is within 50 PSI and your low side within 10-15 PSI, you're probably close enough on charge. If you find you're way out, add refrigerant through the low side port a bit at a time. After each addition, wait for the system to stabilize for a couple of minutes and watch the head pressure (high side). As you get close to the lower limit of head pressure in that chart for your ambient temps, slow way down and let the system do its thing. You can very easily overcharge the system and that'll kill your performance more than being slightly undercharged. It can also kill your compressor!

EricSilver · #13 05-18-2018, 11:13 PM

Based on the chart, my charge (using gauge on low-side) is full to slightly over-full.

The issue I have is the compressor will kick in, refrigerant pressure rises, evaporator temps fall, then a wall is hit and and the values reverse themselves. This pattern occurs regardless of ambient temperature.

Prior to adding some r134 a couple of weeks ago, evap temp would fall to about 41 (with noticeable hissing). Now it struggles to get to 49, and mostly bottoms at 53 before rising. Coldest temps are at idle, particularly after coming to a stop; and then upon accelerating out of that stop.

Seems that either the compressor is shutting itself down; or a sensor is doing it.

Quote:

Originally Posted by Diseasel300

Certainly sounds like that fan motor was singing its last hurrah. Not being familiar with the 210 Climate control, I can't help you further in troubleshooting the CCU/fan module issue. It could be one or the other, or something unrelated entirely, who knows! I try to avoid computerized controls as much as possible, they're such a pain to troubleshoot when something goes wrong.

As far as the A/C performance is concerned, wait for a hot day (85˚+) and check the charge pressures. Make sure when you're checking, you have all 4 windows down, blower on high, temp set low as it'll go.

I know some "supertech" will come along and flame me for even suggesting it, but a decent "rule of thumb" pressure chart against ambient temps will get you close:

Note that the pressures given in that chart assume the car is idling without any additional airflow over the condenser from a separate fan. It also assumes maximum load on the system.

If your high side is within 50 PSI and your low side within 10-15 PSI, you're probably close enough on charge. If you find you're way out, add refrigerant through the low side port a bit at a time. After each addition, wait for the system to stabilize for a couple of minutes and watch the head pressure (high side). As you get close to the lower limit of head pressure in that chart for your ambient temps, slow way down and let the system do its thing. You can very easily overcharge the system and that'll kill your performance more than being slightly undercharged. It can also kill your compressor!

Diseasel300 · #14 05-18-2018, 11:16 PM

It's hard to tell what's going on without knowing the high side pressure, but if the low pressure is high, it would suggest that the system is overcharged. If it is, you can be tripping the compressor out on high head pressure. Cooling performance will also suffer.

sixto · #15 05-18-2018, 11:21 PM

Can you try a known good evaporator temp sensor?

Sixto
98 E320s sedan and wagon
02 C320 wagon