Community,
I'm looking for some advice. My radiator fan flips into high speed once the car turns on. All my coolant levels are good, oil was changed recently, just changed my air filter. The engine temp is well within normal ranges and the A/C is off, does anyone have any clue what is going on?

 

I had this happen on another vehicle . Fans are controlled through sensors and relays, this one had a relay each for low and high speeds. In this case the relay was bad (stuck in closed position) causing the fan to run constantly.
I'm assuming these cars also use fan relays so without the manual in front of me I would suggest looking at the high speed relay. Now that may be my old school showing, the system may be more involved. But I like to start with simple first.
Would like to see what others think.

 

Mud,
Thanks for the reply. Here is my concern, which one of these damn relays controls the cooling fan, God forbid MB to make anything easy. Second, if the relay was bad, wouldn't that mean no power to the fan, not the obverse? I could be totally wrong, just curious. I did some testing, just for my own curiosity, since this started soon after I changed the air filter. I thought perhaps the mass airflow sensor is invloved, so I unplugged it and started the car, nothing changed. Ugh, it could be totally unrelated. I have a cheap code reader I'll plug in tomorrow to see if there are any fault codes, however I think this might be an ECU issue.

 

A relay can be stuck open or closed. I think that your owners manual should be able to identify all fuses and relays, or an online search may yield results. Hopefully they aren't contained within a body or engine control module somewhere. I'm kind of putting the ecu further down the list as there are other items to look into first. I've also heard of but not experienced a cooling fan itself shorted out to max speed but of course something has to be supplying power to it. I don't think that the cooling fan runs constantly .

A cheap obd2 scanner will only let you look at and erase codes. Others here have more info on good scanners but I have the ICarSoft scantool for MB and have just gotten a Konnwei KS850 for general vehicle scan and datestreaming. Theres also Bluetooth scanners that work w phone apps that do the same thing as the 850.

I also have the MB WIS (call it the shop manual) on CD bought for $20 on eBay. That has been most helpful. With your fan on constant high speed, besides a possible relay issue then the question is what is commanding high speed? Then I think about coolant temp or a.c. I know you've you've noted normal temp and a.c. off but a more in depth diagnostic can help to eliminate those as false command possibilites.

 

Happened to me once also, after the car sat a few days at the airport. Got in the car, turned on, went to turn on ac and nothing in the controls were working. Also cooling fan was on high, non-stop.

Got car home....pulled fuse on heater control, looked fine, placed back in. Started car, and everything returned to normal. Has not happened since.

 

Is this a one or two time occurrence or is it happening all the time? My car (2014 E350) will periodically start and the fan sounds like a jet engine about to take off. It does it from time to time and I think its normal. But, if your car is doing it all the time, that is not normal. Sorry I don't have any advice to fix it but wanted to ask the question.

 

 

The fan has its own controller which get the operating signal from the engine control module. 2012 E350 has the M276 engine. Some diagnosis needs to be done before you start replacing parts. It's either going to be the fan assembly or the engine control module. The fan you can buy and do your self..... The engine control module is expensive and you need licensing to be able to purchase. If you are able to purchase then you will need to program it online.

 

I just mention this here but if your A/C refrigerant charge is too high it makes the fan run at high speed at least in my car it does. Your post does not say if any service was done to the A/C system but if this happened check that you don't have overcharge.

 

MBENZTECH,

Are you saying that it's either the ECU or the fan assembly itself? I tried looking for fan relays online for hours and couldn't find it so I'm afraid you might be right or my searching skills need some work. I also have a 2012 E350 4Matic BlueEfficiency with the fan running right when I have the car running. Temp gauge is showing normal so could it be the coolant temp sensor?

 

Do you know where I can exactly locate the relay? I've been searching for hours online for the relay and unsuccessful. The vehicle was previously owned and no manual cam with it.

 

If I remember right (?) the relay is part of the fan control module (mounted on the fan). I need to double check this though. Power is routed through one of the primary fuses internal to the front F32 fuse block but ultimately the fan module is controlled by the ECU. The F32 block is that vertical box next to the battery, has an auxiliary 12v post mounted to it.

Wiring diagram is going to help as it can show all wiring and connections to help with diagnosis. You may consider getting an inexpensive WIS/EPC (shop manual) off eBay or subscribing to something like Mitchell DIY, very reasonable cost. Both will have wiring diagrams.

If there's no signal from the ECU the fan speed defaults to high speed, so as MBenzTech noted there is some diagnosis needed to verify that the ECU signal is present from ECU all the way to the fan module. Pinched wire or corroded connector could be an issue. If signal and power are present at fan module connector then reasonable conclusion is failed fan module. If no signal at connector then verify signal at appropriate ECU output pin. If no signal there then there is a failure within the ECU.

If you don't have a scantool to access vehicle modules then a.c. pressure needs to be checked on high and low sides with gauges. As mentioned I think that the fan also goes high at low system pressure.

 

Have you scanned the vehicle? Sometimes, the ECM can set a code for the coolant temp sensor. This code will also cause the fan to run on high. But the most common problem is the signal coming from the ECU is not the correct one, so the fan defaults to full blast. If I am not mistaken, the signal from ECU to fan controller is between 1.5volts and 3 volts. If it sees 12v, it will go on high.

 

It is an old thread but I assume you have the problem with fan running high...?

If yes, did this start with the hot weather?

if it did then look down a few posts about the A/C charge I wrote. I’m not kidding with this. If your air conditioning is overcharged it will make your fan run full blast and it has nothing to do with your engine temperature.

Try it with air air conditioning system OFF. If the fan slows down your A/C system cannot get the pressure down and it makes the fan run max speed.

With overcharge i don’t mean it is overcharged by MB specs. I mean it is overcharged to work properly in the climate we are.

I had had this happen twice and I let some refrigerant out and it fixed the issue.

 

Hey guys,

It looks like I skipped over a few details that would help diagnose the issue better. No codes showing from the car but then again, I have an OBD2 dongle scanner connected to the Torque app.

Before any of these issues became apparent, the first issue I noticed was a whining noise coming from the belt area. I assumed that it was one of the idle pulleys and decided to hold off (a couple of months) on that since I was going through a life-altering moment recently.

Sunday is when the fan stayed on constantly along with the whining noise from the pulleys/pulley. After sending out my questions on this thread, the car now blows hot air.

I went and got a freon recharger with a dial on it and when connected to the low port, it was showing over-charged. Not sure why it would show overcharged and blowing hot air? I'm thinking the low-end port shows overcharged/high pressure due to a clogged condenser/filter (filter is built into the condenser), or a bad compressor.

Could a bad compressor or condenser/filter be the cause for the fan staying on and the whining noise?

 

You cannot diagnose the hvac system, especially pressures, without either a true vehicle module scanner or gauges that connect to both the high and low pressure sides.
Right now you have no idea what the high side pressures are.
Trying to help you out but you need to take some time to diagnose the system, anything else is a guess.

 

The can mounted gauges show can pressure and you need to understand the system to make them showing system pressure.
System operates on at least 9 sensors, so crystal-balling has low success ratio. Forum has a million, maybe 2 topics about AC troubleshooting, where the procedure is the same for all cars of last 20 years.
You need scanner for W212 models, when some older models could read sensors on car displays.
Seek link to MercedesMedic site.

 

We have a couple experts here who do not want to experiment with anything on the A/C system. If your car is out of warranty let some refrigerant out and see if the fan slows backdown and A/C starts blowing cool again. It is very easy then to re-charge the system back to pressure where it was if you don’t get positive results with this.

A/C system evaporator does not work correctly if the charge is too high on the low side and you do not need a fancy scanner to know that.

Of course you can have multitude of issues but I’m writing this because this same thing happened to me and lowering the charge fixed it. I’m not making this up, it really happened.

P.S. Don’t forget to add oil charge if you end up re-charging the system.

P.S. 2 Checked the A/C low side pressure today (6/12/19). Car on idle, A/C system at MAX COOL, outside temperature 83F by the display in car.

Low side pressure reads 32 psi. Is just a hair above the low range mark on the adjustable dial on gauge.

 

Nobody's trying to be an expert, just trying to lend a hand. Maybe it doesn't agree with your personal repair philosophy but no need to act like an a$$.

 

When W212 is still having white pages on DIY, on older models AC would activate front fan on low only and the only way fan could kick on high was engine temperature, or control unit malfunction.
Overcharge will not affect evaporator. It will kick over pressure sensor ,who will shut the compressor off.
Either way, crystal balling again is not going to work well.
Get your hands dirty and read the scanner.

 

Nobody was acting like a$$ before this post from you. And my troubleshooting philosophy is using brain and hands on skill as much as possible and do what makes sense. Scanner does not do any good if the system is overcharged but not that by MB values they set. That was the case with my car. I had refrigerant level checked by dealer first and they said it is what MB says it needs to be yet I had to let some out to make I work.

 

You are mixing the overpressures. You are talking about on the high side, I'm talking about low side. And absolutely, at least in my car, the high charge level makes the fan run max speed. Made this happen twice and both times the fan came down when letting refrigerant back out while car was running with fan at full speed before letting pressure down.

Perhaps Mercedes did not count for the very hot ambient temperatures that I can experience with 95F in daily basis on summer time. Under the hood temperature must be well north of 100F.

 

Well... we have colder summer this year, so recorded only 110F so far. I still don't recall hearing fan on high in our W212s ever.

 

So, for the heck of it I went on and added refrigerant in my car's A/C system yesterday. I used the fill bottle gauge, which shows both bottle pressure and system pressure depending on how you hold the trigger. I charged the system to 45 psi on the low side with outside temperature at 85F. After this I drove the car for about 150 miles home and it was fine.

Today I drove the cat for about 21 miles and it worked. Stopped for some business for about 40 minutes and no cool coming out of vents. The fan in front starts running at very high speed, which I think is the max speed, but no cooling at all. Outside temperature at 95F and very uncomfortable in the car.

Drove about 8 miles and had to stop as it was so hot. Let refrigerant out to 45 psi by the bottle gauge and got it blowing some cool, not the very best but better than none.

Got home and hooked up the "real" gauges on both sides and when car had been sitting for about an hour it read 100 psi on low side and 150 psi on high side before starting the car. This may or may not be an indication of a problem depending on what kind of expansion valve MB uses in the system. What it tells me is the compressor holds pressure well as I waited another 30 minutes before starting the engine and the pressures did not move at all before that.

When I got the engine running the low side pressure came down to 55 psi and high side went up to 235 psi. Fan in front screaming and very little cooling out the vents. Went on to let refrigerant out all the way down to 25 psi on the low side. Before this point I felt air coming out the vents (could not find the little temp gauge from two parts stores) and it was cooler before than 25 psi when it seemed to get worse. Added refrigerant slowly and the best I could "feel" was with the car on idle, inside fan at second highest speed, temp setting at 65. Pressures read 35 psi on low side and 210 psi on high side.

This was the third time I did this and every time when the low side pressure is at or above around 40 psi the front fan starts screaming and I lose cooling.

I have not found in anywhere what the high side pressure should read. There is lots of info for low side but for some reason I cannot find the high side pressure range.

The system should not be that complicated as it basically is compressing and pumping refrigerant first thru the condenser, where the hot gas turns to liquid, which then travels thru the expansion valve or orifice tube which after the liquid expands and becomes gas again robbing energy inside the evaporator that returns the cooling for the car's interior. Problems usually are either with the compressor or the expansion valve/orifice tube.

I do not know what MB uses as expansion valve but the cars I worked on before had orifice tubes. Before the orifice itself this tube had fine mesh screen. This screen can plug up over time and prevent proper refrigerant flow thru it. This would increase the high side pressure reading but without knowing what it should be it is hard to diagnose.

 

http://www.mercedesmedic.com/ac-air-...le-codes-list/
I've been posting the link to procedure all over the forums, yet for some reason lot of members still go to sledge hammer and crystal ball approach.
Can't explain the mentality, but variable output compressors where computer operates with 7 or more sensors need to be properly troubleshoot.
On W210 the troubleshooting takes 90 seconds as you can do it on car LCD display. while W212 require scanner.
Still easy to test before you start fooling with the system.