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.

http://forum.prevostownersgroup.com/attachment.php?attachmentid=18648&stc=1

[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?

[Ck2hans]

Don’t know why, but reading electrical wiring diagrams just don’t come easy for me. After hours of studying I can make momentary sense out of them (which I forget as soon as I look away). Maybe we can have a seminar at one of the Prevost Expo’s for reading electrical diagrams for dummies.

Chuck

[GarfieldGuy]

Yes I did. After a follow up call with PASS this am they told me the same thing you did. I'm going to take a look at the dash controller this afternoon to see what voltage is coming out of it. Regarding the defrost air continuously blowing air, there is an access door "detail E" on the defroster installation page Y2-2230-00 of the parts manual that opens and closes via an actuator that over time will become detached from the actuator pin. To access from the top requires removal of the majority of trim on the drivers and passengers side. It would require alot of unplugging and replugging of a ton of connections. The alternative method is to remove the front right panel that contains the back up camera and A/C switches. That exposes the actuator and sliding door. They said to start by drilling a quarter size hole above the motor where you should see the dedicated allen screw that may be loose or gone. Then patch the hole. I'm going to start there and see if I can fix the problem.

[Hoffman]

One thing that I didn't see was to explore and confirm there's no blown fuse. I'm thinking of a fuse that controls the step motors on the baffles. My guess.
On my coach, CB79 is labled "DRIVER'S HTR FAN SPEED CTRL MODULE".
A guess.?

[Fratto]

The sample wiring diagram that I posted shows CB79 powering the defrost fan motor but as I understand it, the fan does run. It does not appear to have anything to do with the damper motors though. They are shown to have power from CB28.

It is easy enough to see if these or other breakers are tripped and to confirm that there is voltage coming to and leaving the breaker. Sure doesn’t hurt to confirm this.

Need to confirm all of this though with a diagram specific to his coach.

[GarfieldGuy]

PROBLEM SOLVED!!!!!
I physically followed the 64B wire (fan variable speed) from the blower fan in the dash to the drivers bay and the C11 pin connector bundle which is where I thought it was buried with a thousand other wires. As It turns out, it was not in the bundle but on it's own dedicated wire that was hanging by it's self. I saw the wire previously but didn't want to start chasing another issue until I found the 64 wire. Sure enough, when I looked at the wire label it said 64. Some more fishing around and I found the other half that had become separated from the clip connection which I still can't figure out does. There is no fuse in it. Reconnected the wire and fan works normally. All together the repair cost 600.00 for a new dash control head that I didn't need and 350.00 for a drivers fan speed ctrl module that I didn't need either. At least I didn't have to pay 160/hr to have a prevost tech trace down the problem! http://forum.prevostownersgroup.com/attachment.php?attachmentid=18666&stc=1http://forum.prevostownersgroup.com/attachment.php?attachmentid=18667&stc=1http://forum.prevostownersgroup.com/attachment.php?attachmentid=18667&stc=1

[Fratto]

Nicely done! Glad to hear you got this resolved and are starting the year out on a high note