E320 94 Aux Fan - PeachParts Mercedes-Benz Forum

radunegru · #1 03-02-2008, 09:07 PM

The low speed on the aux fan is not working. If I unplug the blue connector from the thermostat they don't start either. I did change both relays in position B and C and the resistor behind the headlight. Now if I am touching the wires from the red sensor on the receiver dryer the fans are starting. There is another sensor on the dryer (black) that I did not touched. What it should be. Then if I will need to change any of those two sensors I will need a full recharge of the system? Thanks guys

stevebfl · #2 03-02-2008, 09:50 PM

Yes.

radunegru · #3 03-02-2008, 09:51 PM

So witch one is "the one" The red or the Black?

stevebfl · #4 03-02-2008, 10:17 PM

Which one what? I answered the question about whether you would have to discharge and recharge the AC to change either switch. The switch with pigtails runs the low speed fan. The switch with connection at the switch is the low/high pressure switch. It turns the AC compressor off if the pressure is too low or too high.

radunegru · #5 03-02-2008, 10:33 PM

Thanks, thats what I need to know. So the pigtail ones control the low speed fan.

Arthur Dalton · #6 03-02-2008, 11:04 PM

The pigtail is the correct one, but do not assume that the switch is bad..the most likely problem is your a/c system is low on refrigerant and not allowing the high side pressure to get to the cut-in spec pressure of the low fan switch.
Look in the eye-sight and see if you have lots of bubbles..or better yet, put some gauges on the system and see what the high side pressures are.
All as you have done with the jumper is verified the elctrical system for low fan, minus the switch..you have not yet diagnosed the No Low Fan problem.

radunegru · #7 03-02-2008, 11:27 PM

I did checked the system charge first, with a kit that I got from walmart. It looks that the system is charged.There are no bubbles on the receiver dryer.
Do you consider that accurate enough?

Arthur Dalton · #8 03-02-2008, 11:45 PM

No, I don't..Wally unit only measures low side, not high.
..but , a look at the eyesight would be better..many bubbles mean low refrig.

Here is the tricky part:
The low fan is only supposed to come on when the a/c system is under a High Thermal Load ..meaning it is possible in cool ambient temps for the system not to call for low fan...the best time to check is on a Hot/Humid day with a/c on full and at a slightly high idle. At idle , there is little air movement across the condenser and the high side pressure should get to fan sw cut-in spec..if not , the refrigerant change is low OR you have a bad sw. [if the fan ran when you jumpered the sw.] The correct way to tell is w/gauges , but the above will also work for those w/o gauges. All the fan does is it blows additional/aux air across the condenser when the system is being taxed and that additional aux airflow lowers the extreme high side pressures caused by High Thermal Load. It is just aux airflow and is usually not demanded when the car is moving b/c the car movement supplies the required airflow. One usually will see this fan when a/c is on and car is in stop/go traffic. [ High Thermal Load condition example]
Remember this tip:
A NO LOW FAN on this chassis is the FIRST indicator [ in almost all cases] of low refrig charge. The fan circuit verification test is the jumper at the pigtail, but that does not isolate if the problem is sw or low refrig...99% of the time it is low refrig.
A properly operating system will be a cycling low fan at idle on a normal sunny/hot day. The fans aux airflow just keeps the high side pressures in check......that is it's only function and it never comes on if the a/c is not on.
...and if it is NOT a hot day [ high ambients], do not expect to automatically see a low fan . If the system is not burdened , it is not needed and will not come on by design. [ meaning high side fan pressure switch cut-in spec not satisfied/reached, so no demand]

Larry Delor · #9 03-03-2008, 05:47 PM

Would this model have the same resistor that my 420 has? If so, I would check out the wiring on this resistor. Mine has been "repaired" 4 times in the last 4 years - and I know that I am certainly not alone.

Arthur Dalton · #10 03-03-2008, 06:10 PM

He states new R15 droppinng resistor in his first post..and jumper at high side switch verifies resistor circuit OK...

radunegru · #11 03-03-2008, 09:12 PM

Hi Arthur,
Let me tel you what I did .
I hope that I did not run onto other problem.
I checked the receiver dryer and NO Bubbles. Than I got that walmart can and I filed up a bit more. The fan started and now it does not stop at all. Even if I stop the ac. The only think that make them stop is unplugging the pigtail.
What it could be now.
Please help

Larry Delor · #12 03-03-2008, 10:47 PM

Arthur - I read that, but apparently it went into my eyes, and out my _ _ _ .

Sorry 'bout that!

Arthur Dalton · #13 03-04-2008, 02:06 AM

Quote:

Originally Posted by Larry Delor

Arthur - I read that, but apparently it went into my eyes, and out my _ _ _ .

Sorry 'bout that!

Larry.

It shows that you are thinking , cuz the Resistor is in the low fan circuit and is a common fault on such.....so you are excused.....

Arthur Dalton · #14 03-04-2008, 02:10 AM

<>

OK ..sounds like you may now have an overcharge..

See if the fan stops after a minute or two time when the a/c is shut off..it takes a little time for the high side to come back down when a/c is turned off.
Give the sw a few little taps ..you may in fact have a bad/sticking switch.
That is where gauges tell the tale..........

Post findings.

radunegru · #15 03-04-2008, 09:41 PM

You were very right. It may be a sticky switch.The fan stops after 3-4 minutes in Economy mode on the climate control. Maybe because I use one of those walmart cans with R134+sealant? Also the system is not cooling that good as before. What do you think?

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