hobbs air switch on parking brake leak - Printable Version

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+--- Thread: hobbs air switch on parking brake leak (/showthread.php?tid=8754)

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hobbs air switch on parking brake leak - Thekrents15 - 11-15-2025

I have an air leak when you release the parking brake quite audible,  set the parking brake it stops.
I found a hobbs air switch leaking out the back when brake is released ( after a bunch of work to get it out ).

Hobbs - B 76577 4 9613 is the part.

NC contact by labels.

This part appears to be adjustable.  I can't find any info in the forum other than it's tied to the refrigerator lock, interlocks ON brake released
to lock the fridge.

Question, is that it's only purpose?

What is the opening/operating pressure?

There are a mess of replacement air switches with various pressures.

Just get it from Newell...?

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RE: hobbs air switch on parking brake leak - Richard - 11-16-2025

Hmmm, you can also buy them at fixed pressures. I would go with something between 60 and 80

As you have stated, this switch is HOW the electronics know the coach is in park.
The HWH system needs this signal to operate properly and not activate the LEVEL warning light on the console.

And your coach may be different, but my 99 had a manual fridge lock that was not tied into the Park Brake. But you may be talking about the Fridge warning light on the console, which is tied to the park brake switch.

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RE: hobbs air switch on parking brake leak - Thekrents15 - 11-16-2025

Thank you, Richard.
I ran into the HWH slide interlock this morning. Because slide out I wanted it in I just shorted The two leads together and slide came in fine.
When I look for that Hobbs part number it says 4 psi which doesn’t make sense.

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RE: hobbs air switch on parking brake leak - [email protected] - 11-16-2025

(11-16-2025, 11:46 AM)Thekrents15 Wrote:  Thank you, Richard.
I ran into the HWH slide interlock this morning. Because slide out I wanted it in I just shorted The two leads together and slide came in fine.
When I look for that Hobbs part number it says 4 psi which doesn’t make sense.

From the Hobbs catalog, 4 psi is what that part number is. Could be they want it to close with just a little pressure.

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RE: hobbs air switch on parking brake leak - Thekrents15 - 11-16-2025

Jeff,
It is a normally closed contact set.

emergency brake operation:

emergency brake set - no pressure on the output side of the valve.
Hobbs contact normally closed - anything watching that signal knows the parking brake is set
emergency brake released - output side of the valve pressurizes
hobbs switch pressurizes and contacts open - anything watching that signal knows the parking brake is released

My refrigerator lock/unlock is following this switch. With the Hobbs switch removed causing open contact to be seen (pressurized, parking brake released)
the lock/unlock does nothing.

Seems to be a very low threshold, 4 psi, to declare parking brake released.

That is the way I see this is working.

Thank you all for helping me work through ... another air leak

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