Dash air fan

[GarfieldGuy]

My marathon is a 2006. My dash air fan stays on high regardless of the setting. Also the defrost blows continuously regardless of whether it is selected or not. I have replaced the dash control head and the fan speed control. I talked to a MMC rep and they were no help. Anybody have any ideas?

[Fratto]

If these controls are Prevost parts / design, have you tried Prevost PASS? Or were all of your controls replaced with Marathon systems?

[captain2107]

I have a similar issue with my 2006 XL2.

[GarfieldGuy]

I did talk with the PASS folks and they recommended I call the control unit maker MCC. They referred be back to Prevost.

[Fratto]

You should be able to down load the wiring diagrams from Prevost Car. Some times it can be difficult to find what you are looking for in the diagrams, but I would assume that there is a component in common with these two failures.

[Fratto]

Here is an example that I believe to be a 2006. You would need to download the one specific to your VIN number. I might also call PASS again and hope for a different person on call.

[Fratto]

Here is the wiring diagram link

https://techpub.prevostcar.com/en/wiring-diagrams

[Fratto]

If this diagram is anything like the one specific to your bus, I would have thought that the dash controller and the fan controller would have solved the problem. The only thing outside of these two components that seems related to this, is the normally closed magnetic switch shown on the left. I have no idea what this would be doing or where it would be located or if it would cause a problem for the fan speed.

It would be helpful if MMC could explain the logic operation of their controller. That might give you a clue where to look?

[GarfieldGuy]

Mark, thanks for the response. I talked with PASS again yesterday and they thought that the 3 pin C481 off the controller should be showing 12 volts at the middle pin "B" wire 64-1B. I don't have anything. It goes to connector C11 which I found under the drivers seat. It then disapperars into a long light blue plastic buss that I can't trace the wire to. I need to find out where wire 64-1b originates to find out why there is no power on it. There are no breakers popped . We ran out of time yesterday so that's where we left it. I'm not smart enough to determine the origin from the schematic. I did locate the sliding panel motor that actuates the defrost door. It's deep in the dash and it looks like I'll have to remove most all of the trim in the dash area to get to it. It's going to be a huge job.

[Fratto]

If the wiring diagram that I posted fits your bus, the middle wire from connector C481 goes to connector C11 then on to connector C539 (14 pins or so) which connects directly to the Dash Module. So the power source is the Dash Module itself. I might also call MMC back and confirm that the output from their Dash Module is supposed to be 12 volts.

Assuming PASS is correct on the 12 volts, I would work backwards. Check for voltage at pin 30 on connector C11, then check on pin 2 of Connector C539 on the Dash Module.

Feel free to call me at 214-549-4979 any time. Maybe between the two of us we can figure it out.

By the way, did you down load the wiring diagram for your specific VIN?