Ignition on, dash lights up, bus won't start......

[jello_jeep]

Well, there I was in beautiful downtown Lake Havasu City AZ this morning, and was fixin to leave camp. Turned on the ignition key, waited for a couple of moments and hit the starter... Nothing would happen. My dash & gauges were all lit up but the starter wasn't doing a thing.

I cycled the key again and paid more attention this time. I forget exactly what the indicators say, but its like a " check engine" light or something and another one right next to it, that the Prevost book says you should wait until these lights go out before cranking... at any rate these two lights were not lighting up at all and I also noted the display on the tranny control was blank too.

Thinking that my immediate departure was going to have to hinge on someone smarter than I, I called Truk. Belive it or not, his fine wife told me he was ACTUALLY taking a shower, and she was on the other line with CNN to report this unusual behavior on his part....

So plan B was to call Joe at PV Mira Loma... And he helped solve it.

To make a long story short, I had turned on the light in the engine bay the night before, and in fumbling around in the dark to find the switch, I had bumped the remote engine start switch in the bay, off its "normal" setting.

Returning it to its regular "normal" spot instantly resulted in a happy purring series 60....

Sooooo just in case you have similar problems someday, that is the likely cause.

[truk4u]

As I was showering away, mama truk opens the bathroom door and yells, "Jeep's on the phone and can't crank his thingee". I yelled back, "Tell him to use Viagra like he did the last time".

Now he gives you some lame story about the bus not running!

[win42]

Warren: Related to the problem you described. One fairly common starter hesitations is caused by a sticky 24v solenoid located in the electrical panel below the drivers window. These solenoids get sticky at times and have to coaxed to work. Carrying a spare is suggested. I know this was not your case this time but this note may help others trouble shoot a possible problem in the future. These solenoids are not unlike the 6V one used to start my 1931 Model A Ford.

[BrianE]

A little more on Harry's comments. There are 4 of these relays on our coach: 2 in the forward electrical panel under the driver's window and 2 in the rear electrical panel above the engine. All 4 are identical but two control all of the 12v chassis systems and 2 control the 24v systems. Failure of any will shut you down. By the way, Dale (or maybe Kevin) mentioned that most relays can be jumped in an emergency and I'm sure they can if you know what you're doing.
____________________
94 Liberty XL

[jello_jeep]

Interesting, I am carrying some 12v relays along in the parts box.. Do you need a different relay if it is being triggered by a 24v switch ?

[JIM CHALOUPKA]

jello_jeep;Interesting, I am carrying some 12v relays along in the parts box.. Do you need a different relay if it is being triggered by a 24v switch ?

Warren, a relay is an electrical switching devise that allows one to switch various electrical loads and voltages with a voltage of the same or different value. There are two voltages to consider with a relay the control and the controlled. The control voltage is for the coil that moves the contacts to open or close the controlled voltage contacts.

The general case would be that the voltage of the switch controlling any particular relay would also be the operating voltage of that relay. Such as 24v supply, 24v switch, 24v relay. That relay then could be switching something with a completely different voltage and amperage and it could be either AC or DC. In your case the starter would be a DC voltage at a much higher amperage, which would require a very large wire to carry the load. You would not want the large wire running the length of the bus and to a switch on the dash ( the switch would have to be excessively large) and no one would like that). Extra weight and voltage loss also. Both bad . That said it is further possible to have the switch controlling a relay that is controlling the relay you are speaking of and they both could be working at different voltages. I don't think that is the case in this application. I can not think of any reason to wire it up that way.

What you need to do is get out your volt meter and find a helper to activate the switch in question and you check the voltage at the relay. Check the coil voltage.

If you were in an emergency situation You could try the 12v relay in a 24v circuit if the terminals connected up the same. This would be a temporary fix if it worked ( the relay would probably burn out but just might last long enough for one start). To go the other way with the voltage would doubtfully work, because the 12v supply would not be adequate to cause the coil of the solenoid to actuate the contacts for the load. But again in an emergency I would try it.

As mentioned before jumping would also work if you had the right stuff!

In case this is more than you wanted to know, there might be someone else that wants to know.

Some guys are better at jumping than others.

If you want more ask. JIM

[jello_jeep]

Nice description of a relay Jim..

I am familiar with the theory and operation of them, was more or less curious if someone already knew if the control voltage in the 24v (load) relays in the Prevost setup was the same as the 12V. My bad for a too ambiguous question.

Now that I think of it, I belive the mechanic at PVML told me they were the same.

I just like to have some extra parts on board. I read earlier posts about throttle position sensors, and snagged on of those for the goody box already!!

Thanks again.. Nice informative post!!!

[Petervs]

Just to try to reduce confusion on this relay business, consider this:

There are 4 relays on the coach that are like the "master switch" on an airplane. In the front electrical bay below the drivers side window there is a 12 volt master relay and a 24 volt master relay. In the rear engine compartment electrical box there is one of each also.

A relay labeled "12 volt engine run front" on the diagram on the door controls the 12 volt circuits attached to it. The "24 volt engine run front" controls the 24 volt circuits attached to it.

In the rear they are labeled "12 volt engine run" and 24 volt engine run".

Here is the trick:
All 4 of these relays are operated by 24 volt power!

Brian bought me two spare relays that arrived from Prevost the other day. On them it says:
TYCO
VF7 41H11-505
24VDC
Made in Portugal

According to Brian, you can buy part number 'VF7 41H11-505' in both a 12 volt and 24 volt operating voltage. We need the 24 volt for all 4 of our relays.

There is also a nifty little wiring diagram stamped right on the relay that shows clearly which pins to jump to manually operate the system. If you carry a jumper wire with two spade connectors you can wire the relay plug pins permanently ON to get you down the road temporarily.

I hope nobody ever needs to put this business into practice!

[garyde]

Good to know Peter. Does anyone know what the failure rate is for such parts? One or 2 in 5 years? Gary

[JIM CHALOUPKA]

Good post Peter. A question that comes to mind is:are the relays plug in or are the wires screwed to terminals? It would be nice if they plugged in then they could be interchanged easily in an emergency and to trouble shoot. JIM