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'99 ML430, 06 SRX AWD
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328 Posts
Discussion Starter #1
The ML seems to be running warmer than ussual, in traffic, and it is only 60 out. I saw one electric fan switch on in the driveway with A/C on.
How can I verify Fans, temp switch, post circulating pump are functioning correctly.

It is time for a coolant change and would like to check system first.

99 430 109K

Thanks
David
 

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2000 ML55
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565 Posts
Go for a drive to let the vehicle reach normal operating temperature. Then, park in your driveway.

Let the vehicle idle with the hood open and watch it carefully. The fan should turn on within 5 minutes (AT MOST) of sitting in your driveway.

Keep an eye on the temp gauge as well. It shouldn't go over 3/4 wheb the car is idling.

More likely than not, the need for a coolant change is actually your problem. My vehicle always runs cooler with a fresh coolant change.
 

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'07 C280 4matic, '06 530i, '98 ML320
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gw17625410, start the truck, turn the AC fan dial to highest setting, turn off the recirculation (meaning, enable FRESH AIR option), the electric fan should kick in (if the engine is not hot, it will run for few seconds and turn off by itself, if the engine is hot, the electric fan may continue to run).
 

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1999 MTrash 430, its a joke
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190 Posts
The ML seems to be running warmer than ussual, in traffic, and it is only 60 out. I saw one electric fan switch on in the driveway with A/C on.
How can I verify Fans, temp switch, post circulating pump are functioning correctly.

It is time for a coolant change and would like to check system first.

99 430 109K

Thanks
David
What do you consider "warmer than normal"? There are many factors that could lead to the temp climbing on your ml, that might actually be normal.
 

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It was fun while it lasted
2002 ML320, 2005 S430 4MATIC RIP, 2010 F150 Crew Cab
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11,137 Posts
The ML seems to be running warmer than ussual, in traffic, and it is only 60 out. I saw one electric fan switch on in the driveway with A/C on.
How can I verify Fans, temp switch, post circulating pump are functioning correctly.

It is time for a coolant change and would like to check system first.

99 430 109K

Thanks
David
Uhhhh, did you say ONE fan cut on? I don't know about everyone elses but both of the electric fans on both of my ML's run simultaneously. I've never seen just one run. Maybe you have a bad fan motor.
 

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'99 ML430, 06 SRX AWD
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328 Posts
Discussion Starter #7 (Edited)
That is why I was hopeing for a trouble shooting point. Only the Pass side fan went on. I am not sure if one is low speed and the other high speed. Or is one for A/C and the other for more air flow at higher heat range.

Normal operateing temp is slightly higher than 80, as stated above unless I sit still for a period of time then it climbs due to air flow. It has never hit the next hash mark, yet, but it is still cool outside.
 

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Premium Member
02 ML320 06 ML500
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16,934 Posts
That is why I was hopeing for a trouble shooting point. Only the Pass side fan went on. I am not sure if one is low speed and the other high speed. Or is one for A/C and the other for more air flow at higher heat range.

Normal operateing temp is slightly higher than 80, as stated above unless I sit still for a period of time then it climbs due to air flow. It has never hit the next hash mark, yet, but it is still cool outside.
Both elec. fans work in tandem, always. If the A/C is turned on the AAM sends a signal to the fans to be turned on. If the truck needs additional cooling (while not in A/C mode) the Temp. Sensor signals the ECU and then the both fans are turned on. Then depending on the coolant temp, the fans will operate at a slower or higher speed, but regardless they will always operate together.
 

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'99 ML430, 06 SRX AWD
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328 Posts
Discussion Starter #9
Thanks 43,

Is it possible to jump the coolant temp switch like a GM and watch fans ?

Will a generic scan tool, mac / snap on, be able to operate fans manually ?
 

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02 ML320 06 ML500
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16,934 Posts
Thanks 43,

Is it possible to jump the coolant temp switch like a GM and watch fans ?

Will a generic scan tool, mac / snap on, be able to operate fans manually ?
You don't have to jump the sensor. Go the the fuse relay box and pull relay K26. Apply B+ to cavity #5 (corresponding to prong #5 on the relay) and the fans will come on.

The functional tests of components that you speak of is only supported with domestic vehicles.

I went in detail in my original post to inform you that both fans should be running. If one fan is not running, as you say, why are you going elsewhere?
 

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'99 ML430, 06 SRX AWD
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328 Posts
Discussion Starter #11 (Edited)
Ran to McD's for lunch approx. 2 miles water temp at 80.

1) switched on A/C no fan operating

2) Jumped relay and both fans run (I would say high speed).

I now know both fans work.

I have to check if the relay is good. It must be, if there is only one circuit, b/c I know at least one fan ran in driveway after long trip

Possibly there is another circuit for the coolant temp. with a relay ? I am 95% sure only the pass. fan ran in driveway sat. and I am 100% sure it (possibly they) did not run as fast as today.

Could one fan be a two speed fan and the other is a high speed. AAM signals low fan for traffic and both for A/C ?

Thanks for the patience
David
 

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Dallas, Texas
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Ran to McD's for lunch approx. 2 miles water temp at 80.

1) switched on A/C no fan operating

2) Jumped relay and both fans run (I would say high speed).

I now know both fans work.

I have to check if the relay is good. It must be, if there is only one circuit, b/c I know at least one fan ran in driveway after long trip

Possibly there is another circuit for the coolant temp. with a relay ? I am 95% sure only the pass. fan ran in driveway sat. and I am 100% sure it (possibly they) did not run as fast as today.

Could one fan be a two speed fan and the other is a high speed. AAM signals low fan for traffic and both for A/C ?

Thanks for the patience
David
On model '99 fans are wired in tandem. Single speed on/off. Powered from fuse 44 through relay k26.
 

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'99 ML430, 06 SRX AWD
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328 Posts
Discussion Starter #13
OK,

-Fans work physically
-fuse looks good
-Relay tested good

Since everythinging else works in the truck, including the A/C. Possibly, since cold outside, the AAM reads the A/C high side pressure and then activates the fans ?

If the fans are simply overidden by the A/C switch being on, what else would prevent them from running ?

With 90 coming, this weekend, it will be easier to see what works at high temps. LOL

Thanks Again
 

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Dallas, Texas
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Fan relay k26 gets triggered by AAM based on refrigerant pressure or engine temperature.

BTW we are on second page of this thread and you still have not defined what's hotter then normal. OBDII scanner will show you ECT. Normal is 87C.
 

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CL500, SL500, ML320
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Sorry to jump in here, but I have a different problem yet related and was hoping for a bit of direction.....Thanks!!

99 ML320 seems to have a radiator overfllow problem, the light indicator comes on warning of low coolant, the fan doesn't come on and once parked dripps all the coolant (now water) on the ground.

Also, the AC blows warm air and the fan doesn't come on either. Last year the AC was serviced and all was checked. Now it blows warm air even at 60 degree weather (was testing it the otherday).

I checked the AC fuse (F44, 30) and looked fine and still the fan not on when turning on the AC full blast. So far I've been adding water to it when needed and have been keeping an eye on this.
 

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'00 w163 55 amg (sold) '02 w208 55 amg '03 w163 350 inspiration
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711 Posts
rez, he told you. don't interrupt threads. sorry man. see you in the other one that you started?
 

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'00 w163 55 amg (sold) '02 w208 55 amg '03 w163 350 inspiration
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711 Posts
Fan relay k26 gets triggered by AAM based on refrigerant pressure or engine temperature.

BTW we are on second page of this thread and you still have not defined what's hotter then normal. OBDII scanner will show you ECT. Normal is 87C.
witek, tired but my brain will try. is this to say 2 things?
1. the temp guage, even on us mods, is in fact in C's---i probably knew this but want to have verifcation--it makes sense that the guage doesn't read as hi go figure---:p i said I'm tired.
2. your 87C makes sense as the temps in my area are now more pleasant but in traffic put more on the 55 @ idle. I've noticed in numerous threads that optimally 80 on the dial is 'best':confused: but as of late, have also listened and learned from mine that the fan (note single behind radiator) kicks in just above that needle temp point.
 

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Following this thread

Neighbor asked me to look at their ML430 (99) Condensor fans are not working on their vehicle either.
A/C on, engine at operating temp, electric fans would not come on.
Jumped across the K26 relay and fans started up, swapped relays no help.
If I recall correctly the A/c pressures were 125+ on the Hi side and +50 on the low.
I didn't want to add more refridgerant for fear of overcharging the system.
Can anyone shoot me a wiring schematic of the elec fan system?
Or tell me what switches the fan relay looks at on the control circuit so I can check those.
TIA
 

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Dallas, Texas
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6,985 Posts
Neighbor asked me to look at their ML430 (99) Condensor fans are not working on their vehicle either.
A/C on, engine at operating temp, electric fans would not come on.
Jumped across the K26 relay and fans started up, swapped relays no help.
If I recall correctly the A/c pressures were 125+ on the Hi side and +50 on the low.
I didn't want to add more refridgerant for fear of overcharging the system.
Can anyone shoot me a wiring schematic of the elec fan system?
Or tell me what switches the fan relay looks at on the control circuit so I can check those.
TIA
Fans come on at ~240 psi, turn off at ~200 psi. Wiring is in post #12. Trigger method is in post #14. Refrigerant pressure can be read in AAM live data menu.
 
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