U1300l air pressure problems om352 - Benzworld.org - Mercedes-Benz Discussion Forum

dxmedia · 11-18-2012, 12:33 PM

Hiya, problem suddenly started today midway through a drive.

Air pressure is building up to 8 bar and no further. If I empty the tanks they both fill to one bar and no further.

There are no apparent air leaks and the belt on the compressor looks fine. I'm thinking that there's a pressure valve which is jammed?

Is this a known problem and what's the cure?

Thanks,

tmodler · 11-18-2012, 03:44 PM

Could be many things. Get under the truck and find a leak if there is one. It should be leaking a butt ton of air.

If not, you have compressor issues. AV can make you a pretty nice deal on a water cooled unit. I am very happy with mine. Much better than the air cooled POS.

C.

Flint.54 · 11-18-2012, 06:46 PM

I had the same problem in my 406. Is the pressure regulator "kicking out" at 1 bar or will the compressor just not make any more air ? mine was the regulator. The fix amounted to :take the regulator apart....look at it....find nothing wrong....put it back together....fixed! Hopefully you get that lucky too.

TRUKTOR · 11-18-2012, 07:55 PM

The regulator can be the problem, especially in winter,
When moisture in the system can freeze and cause
Thinks to go wonky, especially if the Unimog is equipped
With the earlier alcohol reservoir/anti-freeze system.
In my experience , you can hear the air dumping at the
Regulator / pop off valve. Applying heat to the housing
With a hair dryer has worked to thaw out the frozen
Bits, but it does nothing to eliminate the moisture, so the
Next morning you might have the same problem.
If you have the alcohol system, I'd fill it and re-fill it,
In hopes that it'll chase the moisture out.
Weird stuff happens - I had air-powered alcohol
Eruptions out the top a couple of times...
If you don't hear any air leaking anywhere , then
It would seem to be at the compressor.
It is can be frustrating in the winter when you fire it
Up, and have the fine Winter Mogstink plume enveloping
Your neighborhood ( if not a specific house ), but your
Regulator is frozen and you can't build any air pressure.
You can't leave, because you can't release the parking
Brake, and you can't kill the beast, since the exhaust
Brake is also air operated ( hand throttle was disconnected )...
So it has taken over and you stare at it... Not wanting to
Try and kill it by dumping it into sub-zero frozen gears. I tried to strangle
It at the snorkel .... Didn't work ....
Anyway, if you have had freezing temperatures- I
Would go right to the valve .

dxmedia · 11-18-2012, 10:13 PM

Ok, dumb question, where's the valve?

It's not a leak since the whole thing is quiet and the pressure suddenly stopped building so I don't think it's the compressor at the moment.

The regulator does sound very suspicious.

dxmedia · 11-19-2012, 04:20 AM

I've spoken with Ibbets and they are initially pointing their finger at the pipe from the compressor to the pressure release valve. If it's not leaking air when the engine is off, and it's not dumping, well it's going to be loosing air before the valve.

The unions between the compressor and the valve are known to snap inside the the bolt, and can only be checked by undoing.

Even if this doesn't fix my problem, I think it's good information to have on the board.

If it's not that pipe, I'm going to pull the head off the compressor. There are reed valves, if they become distorted they won't allow pressure to build.

tmodler · 11-19-2012, 04:23 AM

I would put my money on the compressor (reed valves or a warped head).

If it is not building pressure the HAS to be a leak, and that big you would be able to hear it regardless. These compressors move a LOT of air volume at low pressure.

Which compressor do you have?

(Note: I was posting this while you posted the last thing, did not mean to say essentially the same thing, did not see your post.)

C.

dxmedia · 11-19-2012, 06:32 AM

Well the compressor is blowing like a chain smoking hamster.

Looks like the reed valves.

**Nashy99** · 11-19-2012, 01:37 PM

I have had a similar problem with one of my Unimogs I had imported. I have made a fitting that supply's shop air from a seperate air compressor into the air system of the truck. It fits just infront of the regulator/unloader valve.This makes diagnosing leaks a lot easier because you don't need the truck running and makes them easier to hear. Mine turned out to be a severed airline thanks to the guys who washed the truck cutting all of the zip ties on the airlines letting then come in contact with the fan. By placing the line in front of the regulator you can work in both directions and work out if you have a leak, frozen reg or the compressor itself. Hope this helps. Cheers.

**BloodyGerman** · 11-19-2012, 02:14 PM

Quote:

Originally Posted by Nashy99

I have had a similar problem with one of my Unimogs I had imported. I have made a fitting that supply's shop air from a seperate air compressor into the air system of the truck. It fits just infront of the regulator/unloader valve.This makes diagnosing leaks a lot easier because you don't need the truck running and makes them easier to hear. Mine turned out to be a severed airline thanks to the guys who washed the truck cutting all of the zip ties on the airlines letting then come in contact with the fan. By placing the line in front of the regulator you can work in both directions and work out if you have a leak, frozen reg or the compressor itself. Hope this helps. Cheers.

A U1300L in Bundeswehr edition like DXMEDIA has already has the front red air gladhand for that purpose. Comes in very handy for leak testing, or for quick charge up in a garage if you don't want to burn your eyes with mog stink too long.