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Topic: 12 volt air compressor fuse size (Read 402 times) previous topic - next topic

12 volt air compressor fuse size

The tech removed the fuse to my 12 volt hwh air compressor. I can’t find it and can’t find it in the schematics.

How many Amps?
Tom Lang WY6Y (originally  KC6UEC)
and Diane Lang
2003 38 U295 build 6209
2016 Jeep Grand Cherokee Summit Ecodiesel
still have tow-ready 2006 Acura MDX 
Temple City, California
Motorcade 16681 California Chapter President
SKP 16663 member of SKP Park of the Sierra, Coarsegold California
FMCA F071251
Retired electrical and electronic engineer

Re: 12 volt air compressor fuse size

Reply #1
One of them is a 5 amp fuse probably that would be the one.
previous 1984 35 ft ORED 250 HP 3208 Cat        
previous 1998 40 ft U295 CAI 325 hp Cummins
previous 2003 40 Ft u320 build #6140 450 Cummins M11
1999 Mazda Miata
Ron, Nancy, Tipper the cat
currently coachless


Re: 12 volt air compressor fuse size

Reply #3
I tried a fuse, but the compressor runs continuously. Now I know why the fuse was removed. 
Tom Lang WY6Y (originally  KC6UEC)
and Diane Lang
2003 38 U295 build 6209
2016 Jeep Grand Cherokee Summit Ecodiesel
still have tow-ready 2006 Acura MDX 
Temple City, California
Motorcade 16681 California Chapter President
SKP 16663 member of SKP Park of the Sierra, Coarsegold California
FMCA F071251
Retired electrical and electronic engineer

Re: 12 volt air compressor fuse size

Reply #4
As best I can figure there are three ways for the compressor to come on.
1. Make sure the dash switch is off, that opens the air line solenoid to the wet tank, lowers pressure and starts the compressor
2. If the pressure switch is below the start point then it sends a 12v signal to the essex relay to start the compressor.
3. If the HWH system sends a 12v control signal to the essex relay the compressor will start.

Any of these will start the compressor and actuate the 12v NO solenoid on the water trap.  If it is hot then one of them is calling for air.

Removing the fuse disables the switch and solenoid to the wet tank and power to the pressure switch.

If it still comes on them test for 12v at the trigger side of the essex relay.  If it has 12v then the HWH system is calling for air.

If the fuse is in and it is not the HWH system then the pressure switch is closed, the essex relay trigger has +12v and the compressor runs.  The switch could be bad, the compressor may not be compressing or you have a significant leak.  If it is not leveling the coach the compressor is filling the HWH tank which provides pressure to the seal manifolds.  The tank pressurizes to about 90 psi.  The slide seals are regulated to about 12 psi.

To completely disable the compressor and not let the water trap solenoid stay hot, move and merge the HWH control wire and diode (you might have to add a new diode) to the wire from the pressure switch and add an on/off switch between that junction and the trigger side of the essex relay.  Doing so means nothing can energize the essex relay and therefore the compressor and since 12v does not get to the essex relay trigger the water trap solenoid is not energized.

Re: 12 volt air compressor fuse size

Reply #5

If the fuse is in and it is not the HWH system then the pressure switch is closed, the essex relay trigger has +12v and the compressor runs.  The switch could be bad, the compressor may not be compressing or you have a significant leak. 

^ Pulling this out to emphasize it ^

If you cannot get the aux compressor to stop running unless you pull the inline fuse, you have an issue that needs attention.

The primary causes we have seen are a leak in the slide bladder system and a leak at the bottom of the clear condensate bowl that has the NO solenoid on it (or debris on the seat of the NO solenoid plunger), hindering or preventing build-up of pressure.
Learn every day, but especially from the experiences of others. It's cheaper!  - John C. Bogle

Re: 12 volt air compressor fuse size

Reply #6
It is fairly easy to add a 90° turn valve to the bladders to isolate them and a pressure gauge to monitor pressure in them. And add a pressure gauge to the HWH tank too.  When the compressor is off and the water trap solenoid is open there is no pressure from the check valve by the pressure switch back to the compressor.  All of this assumes your system is original, not modified and functioning.  Later models (past 2001) had some factory installed valves.

If you lose the compressor or have no pressure in the HWH tank you cannot deflate the slide bladders.  You can add a small vacuum pump plumbed in properly as a backup to deflate the bladders to allow you to get them in.  It does nothing to reinflate them.

Re: 12 volt air compressor fuse size

Reply #7
Tom,
Is it the original Thomas Brand compressor?  I had the same issue with the compressor never shutting down.  I was confident that I didn't have leakage anywhere so that it never turned off.
I removed the compressor and took the head apart.  Sure enough, the plastic seal inside the cylinder was shot.  One edge had a tear in it.  Even though it sounded normal when running, it was not compressing any air.
They do have a rebuild kit available for a couple of hundred dollars.  I just ended up replacing the compressor.  No promises, but it may be worth a look.
Mark & Bev
2001 U295 36'
Cummins ISC 8.3 350HP
Build #5802
Jeep Wrangler Toad

Re: 12 volt air compressor fuse size

Reply #8
After I run the compressor for a few seconds and then pull the fuse, I can hear the hiss of air escaping for a second. Sounds like it’s coming from the overpressure release valve. I’ll been to cut some cable ties to get to it after I get home from this short trip.
Tom Lang WY6Y (originally  KC6UEC)
and Diane Lang
2003 38 U295 build 6209
2016 Jeep Grand Cherokee Summit Ecodiesel
still have tow-ready 2006 Acura MDX 
Temple City, California
Motorcade 16681 California Chapter President
SKP 16663 member of SKP Park of the Sierra, Coarsegold California
FMCA F071251
Retired electrical and electronic engineer

Re: 12 volt air compressor fuse size

Reply #9
Tom it might be the unloader valve bleeding off air which is normal.
1999 36ft. U320 Foretravel
Build # 5436
1998 Suzuki Sidekick Sport

Re: 12 volt air compressor fuse size

Reply #10
Tom it might be the unloader valve bleeding off air which is normal.


It never stops
Tom Lang WY6Y (originally  KC6UEC)
and Diane Lang
2003 38 U295 build 6209
2016 Jeep Grand Cherokee Summit Ecodiesel
still have tow-ready 2006 Acura MDX 
Temple City, California
Motorcade 16681 California Chapter President
SKP 16663 member of SKP Park of the Sierra, Coarsegold California
FMCA F071251
Retired electrical and electronic engineer

Re: 12 volt air compressor fuse size

Reply #11
Oh! That is a problem.
1999 36ft. U320 Foretravel
Build # 5436
1998 Suzuki Sidekick Sport

Re: 12 volt air compressor fuse size

Reply #12
Mark, the compressor in your coach is the smaller 1/10 hp compressor. In 2002 and later they wend to a significantly bigger 1/3 hp Thomas compressor.  Rebuild kist are available for both. I bought a new smaller one for my coach, rebuilt the original one, sold both and bought the bigger Thomas compressor for much more $$.

This one is about 1/2 the price of the bigger Thomas compressor, has a high duty cycle rating, up to 150 psi.  Other have used these. It might be worth a try.  This source has $50 off and free shipping.
ARB 12V Twin Compressor | CKMTA12|Northridge4x4

Re: 12 volt air compressor fuse size

Reply #13
I’m home now, and after cutting some zip ties and spraying the water trap assembly with 409, a mound of bubbles has shown me where the air leak is. Looks to be one of the threaded fittings at the bottom of the clear water trap, leading to the selenoid.

It’s a tight fit for my fat fingers. Does the clear bowl come off for easier access?  Is one of the fittings screwed directly into the clear bowl?
Tom Lang WY6Y (originally  KC6UEC)
and Diane Lang
2003 38 U295 build 6209
2016 Jeep Grand Cherokee Summit Ecodiesel
still have tow-ready 2006 Acura MDX 
Temple City, California
Motorcade 16681 California Chapter President
SKP 16663 member of SKP Park of the Sierra, Coarsegold California
FMCA F071251
Retired electrical and electronic engineer

Re: 12 volt air compressor fuse size

Reply #14
I’m home now, and after cutting some zip ties and spraying the water trap assembly with 409, a mound of bubbles has shown me where the air leak is. Looks to be one of the threaded fittings at the bottom of the clear water trap, leading to the selenoid.

It’s a tight fit for my fat fingers. Does the clear bowl come off for easier access?  Is one of the fittings screwed directly into the clear bowl?
If it’s like mine yes. There is a aluminum fitting in the bottom of the blasting bowl. Subject to corrosion. Hex head inside. The plastic bowls are prone to crack
Scott
If your going to be dumb, you got to be tough.
June 30, 2020
2001 U320 3610 Barn find
Build 5834

Re: 12 volt air compressor fuse size

Reply #15
I’m home now, and after cutting some zip ties and spraying the water trap assembly with 409, a mound of bubbles has shown me where the air leak is. Looks to be one of the threaded fittings at the bottom of the clear water trap, leading to the selenoid.

It’s a tight fit for my fat fingers. Does the clear bowl come off for easier access?  Is one of the fittings screwed directly into the clear bowl?

It does come off easily, but if you're talking about the condensate bowl, the problem is likely the plastic bowl itself having developed thermal cracks or corrosion of the fittings.

Tutorial with part numbers:

HWH Filters and Bowls
Learn every day, but especially from the experiences of others. It's cheaper!  - John C. Bogle

Re: 12 volt air compressor fuse size

Reply #16
This one may be an alternative to the OEM water trap and solenoid. I used this one in my rebuild.  It is a filter and moisture trap, the bottom valve closes under pressure and opens when pressure is reduced and lets the water out. You can attach a drain tube.  It needs to go in ahead of  the check valve before the pressure switch.

PneumaticPlus SAF3000M-N03BD Compressed Air Particulate Filter 3/8" NPT -...


Re: 12 volt air compressor fuse size

Reply #17
Roger, I would like to copy your setup.  Do you have part numbers for the pressure switch by chance ?

Thank you
Mark & Bev
2001 U295 36'
Cummins ISC 8.3 350HP
Build #5802
Jeep Wrangler Toad

Re: 12 volt air compressor fuse size

Reply #18
Not Roger, but looks like a regular Square D pressure switch, pretty sure any big box store will have them
Richard & Betty Bark & Keiko our Golden Doodle
2003 U320T 3820 PBDS
Build # 6215
MC # 16926
2016 Chevrolet Colorado 4X4 diesel

Re: 12 volt air compressor fuse size

Reply #19
This is the pressure switch I used. I adjusted the upper cutoff pressure from about 90 psi to 95 psi.

I added pressure gauges to the HWH tank, the air bladder and assembly ahead of the pressure switch.

This is the second air filter, 5 micron.
PneumaticPlus PPF2-N02B Miniature Compressed Air Particulate Filter 1/4" NPT...

Wilkerson desiccant drier X06-02-000. (Cheapest I have seen them)
Wilkerson X06-02-000 Dryer,Desiccant for sale online

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