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Robert
Robert, RV Mechanic
Category: RV
Satisfied Customers: 7619
Experience:  18 yrs. RV experience including Cummins North West, Country Coach, Monaco Coach - vendor certified.
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Monaco: RV..Cummins 400 ISL, air pressure governor..sticking..Brakes

Resolved Question:

Monaco RV with Cummins 400 ISL, air pressure governor is sticking causing the Air Pressure to stay high >150 PSI. Brakes and everything still work but the front air releif valve keeps opening to release air from the front tank. It started when we were in freezing temperatures but has not corrected itself once we got to an area above freezing.
Submitted: 4 years ago.
Category: RV
Expert:  Robert replied 4 years ago.

Hi There!!!

 

Thanks for Choosing Just Answer....

 

I would first drain your air tanks. This should have a D2 governor and you can adjust the pressure on them, it is possible the governor has failed. The governor will have a small black cap on top of it, if you remove that you will see a slot you can put a square head screw driver, I beleive the bottom of that will have a nut you have to loosen to allow you to make the adjustment. It only takes small increments to affect the pressure, and if I remember correctly it is opposite so turning to the right should decrease the pressure. IF you need a picture of what the governor looks like then let me know you should be able to spot it in the engine compartment area. Also I would consider changing the air dryer, this should be a spin on, very easy to change but you do want to pump the pressure down with the brakes first before removing. Hope this helps...

 

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Robert, RV Mechanic
Category: RV
Satisfied Customers: 7619
Experience: 18 yrs. RV experience including Cummins North West, Country Coach, Monaco Coach - vendor certified.
Robert and 5 other RV Specialists are ready to help you
Customer: replied 4 years ago.
Is it safe to drive further? I'm about 3 hours from home. Or is having the air pressure that high harmful?
Also, drain the tanks of air or is there a drain for water?
Would the govenor require adjustment after freezing? It worked a couple of times when I first cranked up but suspect that it froze cause we were in 12 deg weather.
Expert:  Robert replied 4 years ago.

OK

 

Anything over 150 and I would be concerned, I went through some testing at country coach with tag raising issues and we were able to adjust the governor up right to 150. On the bottom of the air dryer should be a purge vent valve, make sure that is clear and not frozen. If you had a water separator drain for the tanks I am fairly certain it would be in the front run bay area. I would not advise getting under the coach in the dark and doing this unless you are comfortable (tanks). You could also pump the brakes down and see if that helps once the pressure builds back up. What you do have to watch above 150 is the possibility of lines blowing...

 

Thanks, Robert

Customer: replied 4 years ago.

The Air Dryer purge is something I didn't think of. And I think that is the problem because there is no release of the purge at 120 PSI as normally happens. I looked at the dryer but don't see any ice anywhere. Is there some way to manually active the purge and check this? It is not purging.

 

 

Expert:  Robert replied 4 years ago.

I am not aware of anyway of releasing that pressure with out replacing the purge valve with out the kit. What You may try is drain the brakes down all the way and spin that filter off, don't have to remove it all the way just enough to get the remaining pressure off, once you do this I beleive there is a black vent cap where the purge valve is (on the bottom), you can try to push up on it to see if it is free. Tighten the filter back up, there is an rubber O-ring on that filter but you should be fine to loosen it. This might free things up for you. Never seen one freeze up. It could also be a governor issue.... You probably will also need a strap wrench to loosen that air dryer filter, a belt might work also...

 

Thanks, Robert

Customer: replied 4 years ago.

Do you have a picture of the Air Dryer and where the purge valve is?

Expert:  Robert replied 4 years ago.

OK

 

I am almost 99% certain THIS is the air dryer you have. I always liked the Monaco air dryers because they are the spin on type. Others can be contained in a casing with bolts and this is something you do not want to mess with and would need allot of tools to get to the filter. The newer ones in this style are actually silver, the old ones are black. You might not see the sticker because it could be undercoated if it has never been changed. I would first look in the bays for this filter, on some older Monaco's in front of the side radiator there is a door that opens with a barrel style key and it is there along with a fuel filter. I sent you this so you can see what the purge valve looks like, it is under the black plastic cover on the bottom...

 

Thank You!! Please hit ACCEPT for my efforts, Positive feedback and BONUS welcomed!!!!

Customer: replied 4 years ago.
That is the one I have. I was familiar with the dryer and had located the canister previously. But just wasn't shure where the purge valve was. I bled all the air out and un screwed the filter a few turns. Can't push in on the button on the very bottom. It doesn't move at all. Does it take a lot of force? How hard should I push? Can it be knocked with something?
Expert:  Robert replied 4 years ago.

I would not tap it with anything, it would take allot of force to move it, but you need to be careful about ripping a seal or creating damage to the valve. One thing you might want to try is get a heat gun or hair dryer and try to put some heat to that area, I have never seen one freeze up, in the shop it is change them out with the kit. I would think it is possible for one to freeze since moisture is in that area. I also contacted someone I know who works for the manufacturer of that air dryer and purge valve, however they are on the east coast and I am on the west, if you would like me to follow up with you in the AM I can....

 

Thanks, Robert

Customer: replied 4 years ago.

I can't move the purge valve. So if you can check on that with your friend and let me know in the morning, it would be appreciated.

 

Thanks.

Expert:  Robert replied 4 years ago.

OK

 

I will reply as soon as I find out what his feelings are on this issue....

 

Thanks, Robert

Expert:  Robert replied 4 years ago.

OK

 

This is what I am being told, If the relief valve is popping that means the governor is not doing its job. I don't think the air dryer has anything to do with it. Air is getting through the dryer to the supply tank. The problem is that the governor is not unloading the compressor causing the pressure relief to pop. I would look for a governor line blocked with ice or it could just be a bad governor.

 

Thanks, Robert

Customer: replied 4 years ago.
Ok. Thanks for the quick responses.

You have been very helpful.

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