T1N Cabin Fan Circuits
I have noticed a couple posts about no cabin fan operation at all as opposed to high speed only fan operation. It turns out that there appears to be two different fan motor speed resistor configurations. The following schematics include some notes which may help people to understand the operation.
Added.
A quick check if the Cabin Fan will not operate on all speeds.
The REST and A/C system both utilize fan speed #1.
Enable REST or your A/C system. If the Cabin Fan operates on low speed, but doesn't respond to the other speeds it is likely an ATC module internal fan relay problem. It is NOT the resistor pack because the REST speed #1 needs the resistor pack to be complete for that speed to operate. (It uses all the resistors in series for the circuit.)
Edit:
Always use pin numbers AND wire colors to verify
I find the diagrams less than intuitive, but maybe I'm just not familiar with the conventions. Labels aren't consistent though. I have added some Blue letter designations for this discussion. S209 = Splice #209. C = Connector.
Note that in 8W-42-5 Pin #2 (Blue "A") is labelled "High Side Driver" within the ATC dotted box. In 8W-42-6 (also Blue "A") there is no label at all. (That happens alot.) They are exactly the same point. For me it took referring back and forth using wire colors to 100% confirm that. I find that by MB using one diagram to cover the different flavors the overlapping combined information takes some effort to verify 100%.
As a specific example refer to 8W-42-5 "Blower Motor Resistor Block" dotted box. For the typical NAS aka NAFTA Sprinter fan/resistor circuit, only the pin #4 "Blower Motor +" DG wire applies. The pin #2 C1 has absolutely nothing to do with the circuit. It is for the other variation.
Troubleshooting Tip
With this 8W-42-6 configuration: If the fan works with the key off and REST button on (the relay is fed from Fuse #8), but not otherwise then it MAY be fuse #21 (ATC 12V feed), the actual fan speed selector switch, or the ATC fan relay shown. There could be many other things wrong, but this REST test is a quick and easy way to verify that the blower works at all. If it works on REST, then the problem is not the blower itself, or the resistor block either for that matter.
One step further. If the fan operates on high, but the REST doesn't work then you probably need a new resistor block.
Note the reference to Splice #S362 which is shown in the post.
I have noticed a couple posts about no cabin fan operation at all as opposed to high speed only fan operation. It turns out that there appears to be two different fan motor speed resistor configurations. The following schematics include some notes which may help people to understand the operation.
Added.
A quick check if the Cabin Fan will not operate on all speeds.
The REST and A/C system both utilize fan speed #1.
Enable REST or your A/C system. If the Cabin Fan operates on low speed, but doesn't respond to the other speeds it is likely an ATC module internal fan relay problem. It is NOT the resistor pack because the REST speed #1 needs the resistor pack to be complete for that speed to operate. (It uses all the resistors in series for the circuit.)
Edit:
Always use pin numbers AND wire colors to verify
I find the diagrams less than intuitive, but maybe I'm just not familiar with the conventions. Labels aren't consistent though. I have added some Blue letter designations for this discussion. S209 = Splice #209. C = Connector.
Note that in 8W-42-5 Pin #2 (Blue "A") is labelled "High Side Driver" within the ATC dotted box. In 8W-42-6 (also Blue "A") there is no label at all. (That happens alot.) They are exactly the same point. For me it took referring back and forth using wire colors to 100% confirm that. I find that by MB using one diagram to cover the different flavors the overlapping combined information takes some effort to verify 100%.
As a specific example refer to 8W-42-5 "Blower Motor Resistor Block" dotted box. For the typical NAS aka NAFTA Sprinter fan/resistor circuit, only the pin #4 "Blower Motor +" DG wire applies. The pin #2 C1 has absolutely nothing to do with the circuit. It is for the other variation.
Troubleshooting Tip
With this 8W-42-6 configuration: If the fan works with the key off and REST button on (the relay is fed from Fuse #8), but not otherwise then it MAY be fuse #21 (ATC 12V feed), the actual fan speed selector switch, or the ATC fan relay shown. There could be many other things wrong, but this REST test is a quick and easy way to verify that the blower works at all. If it works on REST, then the problem is not the blower itself, or the resistor block either for that matter.
One step further. If the fan operates on high, but the REST doesn't work then you probably need a new resistor block.
Note the reference to Splice #S362 which is shown in the post.
Last edited: