bus air fan motor won't shut off

On our way home from our first trip in our bus we experienced temperature extremes that had us running A/C during the certain hours of the day and the heater at other times. During a fuel stop, I noticed that when I shut the bus off, there was still a loud fan noise coming from the middle starboard compartment that is secured by screws. I popped it open to reveal the fan for the bus air and it was running. I checked the ignition and also the dash switch that controls air/heat for the bus OTR air and both were off. Ordinarily when I shut the ignition off the fan would also stop. The most immediate way to shut the fan off so that it wouldn't just run off of the battery (I'm assuming this would run off of the chassis battery) was to throw the 24V kill chassis kill switch. I tried cycling it to see if there was a fault that would clear itself, but it would just come back on. During the remainder of the trip the fan continued to run. When I got home, I again shut down the 24V. Is this issue likely to be a faulty relay that is located behind the driver side exterior electrical panel? Anybody run into this problem before?

Thanks,
Devin

Hi Devin. It could be a relay or a contactor. The contactor should be located by the fan. You may need the wiring diagram.
See; http://www.prevostcar.com/cgi-bin/pa...blicationspage

I agree with Gary. It is more than likely a relay. On earlier vintage Prevost coaches the relay enclosure was located in the top of the first bay driver's side, and later it was moved to the condenser compartment.

It will likely be one of the relays that looks like the kind mounted on the firewall of old cars and trucks. It will look like a small silver can.

If you ever have a problem like that, until you isolate the problem just turn off the chassis power using the big switch by the chassis batteries.

I had the exact same problem last summer while driving in considerable heat.

It was a stuck condenser fan relay that caused my problem.

Forgot to mention, one of the most important tools you can own is a good electrical multi tester. It will help you identify these problems easily.

The relay.

I think 24 volt 200 amp continuous service.

I bought a replacement from NAPA. They may not have it on the shelf, but they will have it in the warehouse and available to you in 24 hours or so. I think with tax and tags, near $80.00

Search this form. There is a thread that list the Prevost part number for the relay and a cross reference to a Prestolite(?) number.

PM to Chalupka. I think he found a source on ebay for $12.00 plus shipping.

Hint. Even if you think you turned everything off, use electrical tape to cover all the lugs in the area where you are working when you do the replacement. Else you make a small problem worse and ruin a good wrench or two in the process, not to mention all the other breakers and fuses that go in the circuit you accidentally make alive and overloaded.


These guys

http://http://www.texasindustrialele...com/relays.asp

have this and many others. (I did not check the prestolite number)

15-141
SAS-4401
Your Cost
$53.50

AMETEK 24 Volt DC Universal Applications
Power Up Relays,Pump Motors ,High Current Utility Vehicles, Winches, Lift Trucks,
Snow Plows etc.
Insulated Ground Circuit
Normally Open Circuitry SPST
Contacts : Silver
Voltage Rating 24V DC
Terminals copper; 10-32 thread
and 5/16"-24 thread.
Continuous Rating 200 Amp
Can be used to in place of Prestolite
15-141, 15-196, 15-310,
SAS-4401, SAS-4408, SAS-5401



On edit: Try this link for the thread.

http://forum.prevostownersgroup.com/...ght=prestolite

I had to replace the same relay on the Liberty awhile ago. I used the cheaper one I found at an auto parts store.

It failed, but not fully. So that when you put a meter on it, it registered voltage passing thru the relay, therefore we (Prevost NJ also) thought it was fine. In reality only a few amps were getting thru, enough to satisfy the meter, but not enough to turn over that hunkin motor.

Best pay the extra freight and get a Prevost approved model or at least something heavy duty. I would be concerned about the $12 one.

Attachment 5896

I learned in my years in the Auto industry there are continue use and intermittent use solenoids. You most likely need a continuous use one. Of course they cost more.

Ok, it's been a busy couple days. We got a little bit of snow and I have a lot of driveway to clear -- unfortunately the bus has no roof and it doesn't like the driveway grade with snow on it.

Today I had a chance to open up the box in the condenser bay and found the relays. I identified the condenser fan unit, walked into the Napa about 5 minutes from my house, he cross-referenced it to a Napa/Echlin part (NASCAR Performance endorsed, mind you), and 2 minutes & $75 later I walked out of there with my new relay.

Thanks for the detailed help on this -- I was originally looking for the smaller plug in relays and without the link to phorner's thread I wouldn't have cracked open that box in the bay looking for the expired part.

I'd like to hope that all of my repairs will go as easily as this -- but I know better :o

Wait until you get our bill. These services we provide ain't cheap.