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Jeremy
Jeremy, Certified Truck/Bus Technician
Category: Medium and Heavy Trucks
Satisfied Customers: 3324
Experience:  ASE Med/HD Truck Technician, NATEF Diesel Engines and Electrical/Electronics Technician, EPA 608/609 HVAC Certified, Steering/Suspension and ABS/Brakes Technician
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2007 sterling with Mercedes 450 hp clutch fan willnt shut

Customer Question

2007 sterling with Mercedes 450 hp clutch fan willnt shut off replaced temp sensor for fan
Submitted: 1 year ago.
Category: Medium and Heavy Trucks
Expert:  Jeremy replied 1 year ago.

My name is ***** ***** I will assist you.

Can I get the VIN on this truck so I can see how your fan is operated? I want to see if the fan has any control off the A/C switches (binary switch) or if it is full ECM through the fan solenoid. Sterlings used both methods in 2007 due to the EGR systems on the Mercedes and they used 2 different style fan clutches.

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Customer: replied 1 year ago.

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Expert:  Jeremy replied 1 year ago.

Per my info, you have a Horton. you will have a solenoid on the firewall that controls the fan. Do this check. Remove the air line coming off the solenoid to the fan hub. Do this with the truck off. Start the truck and you should have air coming out of the solenoid. The fan will be engaged. Hook the line up and the fan should disengage.

Now if you have the A/C off and the air pressure is normal, and the solenoid is still kicking out air, unplug it at the harness and it should stop the air flow. If it keeps going, replace the solenoid. If it shuts off, the solenoid is good and you need to move to the electrical.

Your solenoid is completely controlled by the ECM. It gets the signal from the temp sensor and the A/C switch. You will have to check for input to the ECM from the temp switch and the A/C. If you are comfortable doing the pin tests with small electrical pin tester tools to slid into the harness (not puncture, just slide the pin into the connector) let me know and I can load up diagrams for you to do the pin testing. If not, I suggest having a mechaninc do it. It takes about 30 minutes for the mechanic to do it, but they can test it faster with the truck software so they won't need to pin test it.

Rule out the solenoid and the fan clutch first. Let me know the result of that and we can continue. The solenoid test should take about 20-25 minutes to do.

To see if the ECM is sending the signal correctly (after the solenoid test is done and ruled out) and that the ECM isn't shorting out, start the truck, build the air pressure up with the hood open (so you can see the fan) and rev the engine to max RPM for 5 seconds. The fan should disengage to allow full horsepower, then cycle on and off every 10-15 seconds. If you are not getting the cycling, the ECM could be grounding internally. This rules out the ECM for it will bypass all functions it is reading and cycle the fan to allow the truck to produce most horsepower. All Mercedes are programmed that way.

Customer: replied 1 year ago.

unplug ac sensor and still fan runs if I unplug the solenoid for the fan with it running the fan stops

Expert:  Jeremy replied 1 year ago.

If you rev the engine up, does the fan stay engaged?

Your issue will be in the engine temp sensor or the ECM. I'm hoping it is in the engine temp sensor. It could be in the A/C switch, but you unplugged it so there should have been no signal to the ECM. Unplug the engine temp sensor and see if the fan stays engaged. If it kicks out, replace the sensor.

Expert:  Jeremy replied 1 year ago.

I see you viewed this and this is still showing as a open question due to no positive (3 stars or more) rating.

Did you still need assistance with this?

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