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Old 11-20-2016, 07:07 PM   #1
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Help, What the Heck Is This Part, What Does it Do.

Hi,

Here are the specs,
1997 Freightliner Liner Chassis
Tiffin Allegro Bus 32' DP
ISB C 275 24 Valve

We were returning from our last adventure and noticed that the unit in our MH that normally makes a buzzing/chipping sound started to increase it's interval of operation. Normally this makes a sound about every 40 seconds, now it's down to about every 10-15 seconds. This part is located on the front firewall and had a couple of wire leads and a small vacuum type hose attached.

I thought that it might be part of the compressed air system and dumped the chassis air and drained the tanks. No water was released on the tank drain.
The air pressure maintains it normal location on the gauge. Both needles at about 110-120 PSI with normal cutoff at 120 PSI

I started the MH back up and the interval was back to about 40 seconds or so. Now after taking it to refuel and dump the holding tanks, it back to 10-15 seconds.

I'm at a loss and concerned that this may be more important that I understand. Not knowing is not the best place to be on these complex beasts.

Attached is a photo, any information would be appreciated as we are supposed to leave the day after Thanksgiving.

TIA,

J R Setser
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Old 11-20-2016, 07:14 PM   #2
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Looks a lot like a vacuum pump for the AC/heater controls. Normally has a ball shaped reservoir associated with it.
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Old 11-20-2016, 07:19 PM   #3
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Quote:
Originally Posted by xydial View Post
Looks a lot like a vacuum pump for the AC/heater controls. Normally has a ball shaped reservoir associated with it.
Exactly right. Diesels don't create a vacuum so they add a pump and accumulator tank to compensate. The accumulator tank is the "ball shaped reservoir" mentioned, they can also be other shapes but the ball is more common.
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Old 11-20-2016, 07:35 PM   #4
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i see a white fitting is a hose missing ?
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Old 11-20-2016, 08:08 PM   #5
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Help, What the Heck Is This Part, What Does it Do.

Hi,

Ok, yes there is a round ball shape attached at the end if the vacuum hose.

Does the increase interval mean that the pump is failing?

Could it be a vacuum leak in the hose or is the pump shot.

Where the heck would I get a replacement.

Glad to find out the coach will still stop when I hit the service brake.

Anyone have any additional insight.

TIA,

J R
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Old 11-21-2016, 08:13 AM   #6
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Could it be a vacuum leak in the hose or is the pump shot.
Yes (could be either). A cracked or disconnected hose is the most likely, however.

The position of the dash a/c & vent controls may have an effect on it, since the basic purpose of the vacuum pump is to operate the doors that open/close/divert air to various outlets, e.g. defrost vs heat vs vent or to control the air temperature mix.
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Old 11-21-2016, 08:36 AM   #7
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Thanks Gary,

I'll check on that right now.

You just have to love IRV2. Without the help I receive here, owning a MH would be much more expensive.

Once again, thanks to all the posters for your help,

J R
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Old 11-21-2016, 10:09 AM   #8
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Definitely a diesel vacuum pump. Looks identical to one I have installed several times....believe it or not it's the same part as the one in a C4 ZR-1 Corvette!
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Old 11-21-2016, 01:32 PM   #9
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Hi,

Following Gary's advice, I went out and cut 1" off of the vacuum hose running to the unit from the reservoir. The hose end was pretty brittle and this appears to have fixed the problem.

Thanks all,

J R
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Old 11-21-2016, 02:06 PM   #10
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Originally Posted by hooptie00 View Post
Hi,

Following Gary's advice, I went out and cut 1" off of the vacuum hose running to the unit from the reservoir. The hose end was pretty brittle and this appears to have fixed the problem.

Thanks all,

J R
Cool, that'll be $5.
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