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Old 07-30-2021, 05:05 PM   #1
Skoolie
 
Join Date: Jul 2019
Location: Suburbs of Winterset, OH
Posts: 242
Year: 2005
Coachwork: Thomas
Chassis: FS65
Engine: Mercedes 6.4L
under body fans won't shut off

Today I had a A/C tech out...charged the A/C system that is staying on the bus.
However, after shutting the bus off, the underbody fans kept running. Initially I thought that they were either on a timer or a thermal switch...after over an hour, they were still running.

Looking for a relay, I located a small box connected to where the fans are mounted..wires go to the fans, I pulled the fuses out of that box to stop the fans. Can anyone advise if there is a relay or some sort of switch that could be malfunctioning.

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Old 07-31-2021, 06:09 PM   #2
Skoolie
 
Join Date: Jul 2019
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Year: 2005
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Chassis: FS65
Engine: Mercedes 6.4L
Today I tried changing the on/off switches, made no difference.
I did notice that on the rear system, that was always working, the ignition key has to be on before the circulating fans come on. On the front system, which is the problem, the ignition switch does not need to be on. The circulating fans will come on when the switch is turned on.
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Old 07-31-2021, 08:15 PM   #3
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Sounds like an obvious relay somewhere, have you traced the wires from both ends to see if anything is connected in line?
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Old 08-01-2021, 08:32 PM   #4
Skoolie
 
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Year: 2005
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Chassis: FS65
Engine: Mercedes 6.4L
the wires disappear into the abyss....I'll start pulling panels off tomorrow..maybe start at the switches on the dash as that panel was easy to remove.
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Old 08-02-2021, 07:14 AM   #5
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Trans / AIR will have a record of this and should be able to provide you with what relay board is used and where it is.. on my Trans / AIR unit, the circuit panel is under the bus and the relay board is inside the plastic cover of the evaporator, tucked up near the wall. you may actually be able to tap on the relays with a screwdriver handle when the system is turned off and get it to disengage if it is stuck.. the only way I could see mine was to pull the plastic cover off of the unit. you might be able to pull the metal filter off the bottom and shine a flashlight up in.. on mine the wiring board is on the same side as the conduit where the pipes go up into the unit. (this is all on the inside unit for that system)
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Old 08-02-2021, 02:56 PM   #6
Skoolie
 
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Chassis: FS65
Engine: Mercedes 6.4L
thanks! however....and the reason I don't like electrical issues...
This morning, I disconnected the negative battery cable..then began tracing the wires from the A/C switches...quickly located another panel where those wires connected...panel was under the dash, under the glove box, semi behind the diesel heater blower housing..actually easy to get to..so I switched what I figured were the relays between the 2 A/C systems. Reconnected the negative cable to the batteries...nothing, no power to anything...multi meter shows extremely low voltage, 4 to 6 volts..I'm sure that nothing was left on to completely drain the batteries. I hooked up my battery charger, still nothing, no lights, nothing works. I took the cables off the batteries, hooked the cables up to the battery charger, still no lights...There is a 20 amp fuse in the smaller wires coming from the batteries, that fuse is ok. I did not check for power before disconnecting the batteries so I don't know if the batteries were drained before I started messing with the wires. I suppose it's possible that the batteries crapped themselves over night....but not likely. Right now, I have the batteries disconnected and am recharging them one at a time.
Suggestions are welcome!
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Old 08-03-2021, 08:36 AM   #7
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First off, if you turn your thermostat all the way down the fan will turn off so that you donít run your battery down.

Second, Iíve been told these units are usually added on after market. They should both be hooked up to the ďIGNĒ terminal on one of your boards. It sounds like one is on ďBATĒ. Have you had this bus for a while? Not used the AC much? I seems that if one was wired to BAT, it would have been a problem before.

I had the opposite problem. One of my fans was not coming on. This caused my compressor to overheat and expel freon. The fix was the Big relay (70amp I think) on my AC board. A friend used his meter while I turned knobs and listened for fans until we figured it out. I helps to have one healthy unit to compare it to and switch around parts.

I have a Thomas Pusher 2001 and I see you have a fs65 but I will take pics of my boards and relays when I get to my bus later today.

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Old 08-03-2021, 01:03 PM   #8
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Ok. I have this up above my windshield. The relay Iím pointing to is the one I replaced so that my fans would come on. IMG_0534.jpg

Outside under my drivers window I have 3 boards. The black wires Iím holding go to my 2 fan units. Both are connected to ďIGNĒ and both come in thru the relays/or breakers shown in the last pic. IMG_0535.jpg
IMG_0537.jpg
IMG_0536.jpg
Maybe you have something similar?

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Old 08-03-2021, 03:51 PM   #9
Skoolie
 
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Chassis: FS65
Engine: Mercedes 6.4L
image 5202..I traced wires from A/C on/off switch to this panel. swapped relays from rear A/C system (that was working)with relays on the other A/C system I am working on.

Image 5203same panel as image 5202,,,thats a 15 amp fuse, if the fans are running, pull that fuse, fans stop and stay off until the A/C system is turned on again with the ignition switch on.

image 5204 another panel just above the panel shown in image 5202 and 5203
I don't think it has anything to do with the A/C

image 5205, panel under drivers window, I pulled all the relays one at a time while fans were running...nothing happened.
Attached Images
File Type: jpg IMG-5202.jpg (202.6 KB, 4 views)
File Type: jpg IMG-5203.jpg (224.5 KB, 4 views)
File Type: jpg IMG-5204.jpg (228.3 KB, 4 views)
File Type: jpg IMG-5205.jpg (260.2 KB, 4 views)
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Old 08-03-2021, 03:56 PM   #10
Skoolie
 
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Year: 2005
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Chassis: FS65
Engine: Mercedes 6.4L
I'm thinking that I may just cut the wire to the small blue 15 amp fuse, insert a toggle switch, which I'd locate on the control panel next to the A/C switch...seems that once I interrupt the power to the fans they stay off until the A/C system is used again. If I forget to turn the switch on, the fans won't run...if the fans don't run, I think the underbody heat exchange thingy would ice up...not good, but not catastrophic either.
Please excuse the technical language (thingy, whatchacallit and thing-a-ma-jig)
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Old 08-03-2021, 03:59 PM   #11
Skoolie
 
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Year: 2005
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Chassis: FS65
Engine: Mercedes 6.4L
I forgot, the only thing over my windshield are the wiper motors.
and...me thinks me left the parking lights on...battery went down before the sun so no one noticed the lights.
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Old 08-04-2021, 09:00 AM   #12
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IDK. When your fans arenít on the Freon heats up and blows out the back of your compressor. As I said, that happened to me. So if you do that, never forget to turn fans on.

You never did say when the problem started. Came that way? Something you changed?

One reason I say that is on one of your AC boards you have 5 relays and on the other you have 2. Sup with that? Is the first thing I would ask.

Iím not an expert. Iím just a guy like you who had to figure some stuff like this out. The more replies to your thread, the more attention it will get.

Peace
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Old 08-04-2021, 10:37 AM   #13
Skoolie
 
Join Date: Jul 2019
Location: Suburbs of Winterset, OH
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Year: 2005
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Chassis: FS65
Engine: Mercedes 6.4L
When I bought the bus, the rear A/C system worked fine. The front system...did not work, the seller replaced the compressor and tried charging it, which revealed a significant leak. The seller showed me the location of the leak. I replaced the rusted/leaky part which was a steel 90 in the a/c coolant line under the bus.
I had a A/C tech out to charge the front system...he put a vacuum on it and detected more leaks...he said to replace both of the charge ports located under the hood...did that, the A/C tech came back out, charged the system..it cools fine. That was when I discovered the problem with the fans.
I'm getting ready to disconnect the batteries again...to see if I have a draw on them...if I do, maybe it's the faulty relay drawing power to disconnect??? If that's the case, maybe my toggle switch idea isn't such a good idea afterall...
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