Rad fan on high speed
Thread Starter
Junior Member
Joined: Oct 2019
Posts: 64
Likes: 22
2016 E400
Rad fan on high speed
2012 W212 3.5 gas wagon.
Cooling fan for the past month or two starts to run up to full speed shortly after starting the engine. Scanned for codes, other than one for a damaged left rear wheel speed sensor, nothing in the ECM or AC modules.
Live data shows the AC controller (when turned off) is at 1% for fan speed however the ECM fan control speed ramps up to 90% shortly after starting the engine.
Engine coolant temp via the scan tool looks completely plausible.
The AC pressure though shows 21 bar which in my world is over 300psi. I hooked up a set of gauges to the high and low side, with the AC off and outside temp at 8c, the pressures are both in the 50psi range.
So, it appears that the AC pressure switch is bad. My question is, will such a high pressure reading to the ECM cause it to command the fans on high?
If so, next step is to examine the harness at the switch and have the system discharged to install a new switch.
If the high reporting AC pressure (even with the AC turned off) does NOT cause the ECM to command the fans to 90%, what next?
Thanks, Dave
Cooling fan for the past month or two starts to run up to full speed shortly after starting the engine. Scanned for codes, other than one for a damaged left rear wheel speed sensor, nothing in the ECM or AC modules.
Live data shows the AC controller (when turned off) is at 1% for fan speed however the ECM fan control speed ramps up to 90% shortly after starting the engine.
Engine coolant temp via the scan tool looks completely plausible.
The AC pressure though shows 21 bar which in my world is over 300psi. I hooked up a set of gauges to the high and low side, with the AC off and outside temp at 8c, the pressures are both in the 50psi range.
So, it appears that the AC pressure switch is bad. My question is, will such a high pressure reading to the ECM cause it to command the fans on high?
If so, next step is to examine the harness at the switch and have the system discharged to install a new switch.
If the high reporting AC pressure (even with the AC turned off) does NOT cause the ECM to command the fans to 90%, what next?
Thanks, Dave
MBWorld Fanatic!
Joined: May 2021
Posts: 2,524
Likes: 2,041
From: US
2008 E350, 2012 ML350, 2014 E350, 2015 ML350
2012 W212 3.5 gas wagon.
Cooling fan for the past month or two starts to run up to full speed shortly after starting the engine. Scanned for codes, other than one for a damaged left rear wheel speed sensor, nothing in the ECM or AC modules.
Live data shows the AC controller (when turned off) is at 1% for fan speed however the ECM fan control speed ramps up to 90% shortly after starting the engine.
Engine coolant temp via the scan tool looks completely plausible.
The AC pressure though shows 21 bar which in my world is over 300psi. I hooked up a set of gauges to the high and low side, with the AC off and outside temp at 8c, the pressures are both in the 50psi range.
So, it appears that the AC pressure switch is bad. My question is, will such a high pressure reading to the ECM cause it to command the fans on high?
If so, next step is to examine the harness at the switch and have the system discharged to install a new switch.
If the high reporting AC pressure (even with the AC turned off) does NOT cause the ECM to command the fans to 90%, what next?
Thanks, Dave
Cooling fan for the past month or two starts to run up to full speed shortly after starting the engine. Scanned for codes, other than one for a damaged left rear wheel speed sensor, nothing in the ECM or AC modules.
Live data shows the AC controller (when turned off) is at 1% for fan speed however the ECM fan control speed ramps up to 90% shortly after starting the engine.
Engine coolant temp via the scan tool looks completely plausible.
The AC pressure though shows 21 bar which in my world is over 300psi. I hooked up a set of gauges to the high and low side, with the AC off and outside temp at 8c, the pressures are both in the 50psi range.
So, it appears that the AC pressure switch is bad. My question is, will such a high pressure reading to the ECM cause it to command the fans on high?
If so, next step is to examine the harness at the switch and have the system discharged to install a new switch.
If the high reporting AC pressure (even with the AC turned off) does NOT cause the ECM to command the fans to 90%, what next?
Thanks, Dave
Out Of Control!!
Joined: Apr 2019
Posts: 11,923
Likes: 6,776
From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
RIGHT ON!
2012 W212 3.5 gas wagon.
Cooling fan for the past month or two starts to run up to full speed shortly after starting the engine. Scanned for codes, other than one for a damaged left rear wheel speed sensor, nothing in the ECM or AC modules.
Live data shows the AC controller (when turned off) is at 1% for fan speed however the ECM fan control speed ramps up to 90% shortly after starting the engine.
Engine coolant temp via the scan tool looks completely plausible.
The AC pressure though shows 21 bar which in my world is over 300psi. I hooked up a set of gauges to the high and low side, with the AC off and outside temp at 8c, the pressures are both in the 50psi range.
So, it appears that the AC pressure switch is bad. My question is, will such a high pressure reading to the ECM cause it to command the fans on high?
If so, next step is to examine the harness at the switch and have the system discharged to install a new switch.
If the high reporting AC pressure (even with the AC turned off) does NOT cause the ECM to command the fans to 90%, what next?
Thanks, Dave
Cooling fan for the past month or two starts to run up to full speed shortly after starting the engine. Scanned for codes, other than one for a damaged left rear wheel speed sensor, nothing in the ECM or AC modules.
Live data shows the AC controller (when turned off) is at 1% for fan speed however the ECM fan control speed ramps up to 90% shortly after starting the engine.
Engine coolant temp via the scan tool looks completely plausible.
The AC pressure though shows 21 bar which in my world is over 300psi. I hooked up a set of gauges to the high and low side, with the AC off and outside temp at 8c, the pressures are both in the 50psi range.
So, it appears that the AC pressure switch is bad. My question is, will such a high pressure reading to the ECM cause it to command the fans on high?
If so, next step is to examine the harness at the switch and have the system discharged to install a new switch.
If the high reporting AC pressure (even with the AC turned off) does NOT cause the ECM to command the fans to 90%, what next?
Thanks, Dave
You've crossed all the T's including harness inspection!
The ECU reads "300.Psi" as A/C pressure where in fact your gauge set says 50psi.
This is sensed by a voltage measurement through a variable resistor - Check for water oxidation on both sides of the connector.
Then RTV Silicone all the low hanging connectors you see around there ... the MB wiring seals leak!
Last edited by CaliBenzDriver; Nov 11, 2024 at 04:17 PM.
MBWorld Fanatic!
Joined: May 2021
Posts: 2,524
Likes: 2,041
From: US
2008 E350, 2012 ML350, 2014 E350, 2015 ML350
I am very confused , I have a 25 year old MB and I get 15-17 bar all the time for excellent cooling and yes changed the pressure sensor years ago
you on the other hand are questioning 21bar when your high side pressure sensor is good for 0-35bar
Plus your AC controller receiving pressure data is the one that sets the target fan speed and communicates that request to your ECU
I think you need put the gauges on and record while running the H and L pressures
you on the other hand are questioning 21bar when your high side pressure sensor is good for 0-35bar
Plus your AC controller receiving pressure data is the one that sets the target fan speed and communicates that request to your ECU
I think you need put the gauges on and record while running the H and L pressures
Thread Starter
Junior Member
Joined: Oct 2019
Posts: 64
Likes: 22
2016 E400
The car is not mine, I was told the AC was working ok this summer but today is only 4c outside so its difficult to confirm. Resting, AC off, 4c outside temp the pressures are approx 40 lbs H and L on my manifold set. The scan tool reads 19.7 bar though. Clutchless variable displacement compressor engaged, the max amount of current I could coax it to consume was just over 1 amp on the tool, I assume due to either the low outside temp or perhaps a low charge, or because the AAC module is receiving a high pressure reading? At 1amp draw, the scan tool pressure rose slightly over 20 bar and the gauge set L dropped slightly, the H side rose only slightly to 60 psi or so which I think is pretty normal for compressor that is only slightly pumping. 20 bar is pushing 300 psi, I'm certainly not seeing that on my manifold gauges.
Our dealer has 6 pressure switches in stock and says they are a common failure item. I'm waiting for the ok to have the system discharged so I can replace the switch.
Our dealer has 6 pressure switches in stock and says they are a common failure item. I'm waiting for the ok to have the system discharged so I can replace the switch.
Last edited by OntarioDave; Nov 12, 2024 at 01:18 PM. Reason: Add
Member
Joined: Aug 2004
Posts: 135
Likes: 14
From: Sweden
2013 E250CDI BlueEfficiency 4Matic
OntarioDave My vote goes for replacement of the AC Pressure sensor, my car showed similar problems and a new (MB original) solved the problem.
Thread Starter
Junior Member
Joined: Oct 2019
Posts: 64
Likes: 22
2016 E400
I removed the lower cover last evening and inspected the plug, looks fine, no corrosion etc. Fan doesn't spool up to jet engine speed with it unplugged. Guess I'm on the right track ....
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Thread Starter
Junior Member
Joined: Oct 2019
Posts: 64
Likes: 22
2016 E400
Had it evacuated, installed the new switch, scanned it to display just under 2Bar prior to vacuuming the system. Refilled AC with 590g of 134 and we are back in business. Fan operates normally now. Thanks for the replies.
Dave
Dave
Out Of Control!!
Joined: Apr 2019
Posts: 11,923
Likes: 6,776
From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
right on Dave!
Your research saved you a ton of troubles and a big bundle...
glad we could help you stay on course to enjoy MB ownership.
glad we could help you stay on course to enjoy MB ownership.
Last edited by CaliBenzDriver; Nov 16, 2024 at 08:43 PM.
Thread Starter
Junior Member
Joined: Oct 2019
Posts: 64
Likes: 22
2016 E400
Now on to repair a couple other issues, foremost is the dome light that works when it likes. No coms with the overhead console module. I pulled it down and it appears there was a mouse living (and urinating) on top of the module. I took it apart and the board is a corroded mess. A new one is over $1k Cdn, time to look on Ebay....
