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?