cmueller88

I have a 2001 ML55. It started overheating when I was stuck in line to get into Disneyland.
When I turn my A/C on the fan does come on and my temp goes down to operating temperature.
What could be causing my ML55 to over heat?
Why doesn't the fan come on when the temperature rises to high?

Thank you.

gsfent

Bad high temp fan switch/relay? Most cars have a high temp switch/relay, as well as a partial override when the AC kicks in (puts fan on low speed as a default).

Either search, or perhaps someone here knows which switch/relay is most the likely culprit. Most often the replacement is DIY.

Regards,
Jerry

Maj. Dundee

The first thing you have to do is check the 100 amp fuse near the battery. With a test light or DVOM check for B+ voltage at both sides of the fuse.

If the fuse is OK, then you must conduct tests at the ECU for the Coolant Temp. Sensor. Do you have a DVOM?

cmueller88

I will check the 100 amp fuse. I will let you know if it is good or not. I have a DVOM.

Thank you.

cmueller88

Thanks for all your help. It was a bad temp switch.

AMG714

I am a new owner and having the same issue ... I looked for the 100amp fuse near the battery and could not find it ... Also was trying to locate the relay/switch and I am unsure if it's the one attached to the fan or elsewhere. Hope I can get some help with this thanks.

Maj. Dundee

Did you look at the photo above?

AMG714

Yes and my engine bay looks nothing like that lol I have a 2001 ML55 AMG so that might be why it does not look like that?

Maj. Dundee

Well then post a picture of your eng. bay exactly as shown in the photo.

AMG714

Here is a few pics from different angles thanks.
2001 ML 55 AMG:
https://www.icloud.com/photostream/#A3G4VTwGGTOMEc

Maj. Dundee

Both of the photos match. You just have to find it.

cmueller88

I was able to finally find the temp switch for the fan. If your looking at the engine, on the front left side of the engine is where the switch is located. I believe there is a small clip that holds it in place. I also remembered that the o-ring did not originally come out when I pulled the switch out. Make sure you get the old o-ring out before you put the new switch in, and that the new switch has a new o-ring.
I will try to get pics, but may not be able to until this weekend.

AMG714

Nope sorry I don't have one ...