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dansawyer · 11-17-2022, 11:02 PM

The RV is a 2002 National Tradewinds with a Cat 3126E on a Spartan chassis. We were heading into Bosie and I noticed the pressure was below 100 where it normally turns on the compressor. Nothing. A few more miles - nothing. Some breaking for traffic and it definitely was not turning on, it was dropping to 90. I pulled off and as as luck would have it there was a huge empty parking lot.

Before I get a tow to an RV dealer or Cat dealer I would like to check anything simple I can check.

Is there a fuse?

Where is the pressure sensor?

Is there a circuit diagram somewhere?

Thank you in advance. Dan

gpounder · 11-17-2022, 11:21 PM

There is a great chance the air governor valve is stuck. Read up about it. Many are made by Bendix. If you can get to it give it a whack. If your handy they can be replaced fairly easily.

dansawyer · 11-18-2022, 01:55 AM

Thank you.

I found a picture if it is the same one.

Any chance you know where it is? I have not seen anything like that.

It looks like the connections are air lines. Is that correct ? If so it is a mechanical device?

triplewide · 11-18-2022, 02:58 AM

Are temperatures below freezing where you are? Maybe will start working if/when it warms up. May have some moisture where it shouldn't.

twinboat · 11-18-2022, 03:38 AM

The governor is a air valve and it controls the compressor which is a mechanical pump turned by the engine.
Nothing electrical will effect your air system except maybe any dump valves, and that wouldn't let the air drop below 70 PSI.

Most owners replace the governor and then go on to find and fix the real problem. It's cheap and easy to change but rarely the problem.

I suggest you call a mobile mechanic and have someone with air brake knowledge check out the system.
If you had regular brakes and the pedal went to the floor, could you fix it or call someone.

dansawyer · 11-18-2022, 07:36 AM

Quote:

Originally Posted by triplewide

Are temperatures below freezing where you are? Maybe will start working if/when it warms up. May have some moisture where it shouldn't.

Yes. We were in Pendleton OR in a 'freezing fog'. This worked for about 3 hours after that and then it quit. When I saw that the part was mechanical I thought of ice.

I can get air from a portable compressor. I will add air and start bleading the tanks to see if there is any water.

MN_Traveler · 11-18-2022, 07:56 AM

Following. Good thing you got onto the flat terrain before this happened.

Are you sure it is the compressor not running and not a leak (which you would hear if walking around outside)

wolfe10 · 11-18-2022, 07:59 AM

First, check for a substantial leak. Air it up (engine running) until dryer purges. Turn off engine and listen for a leak.

Next, suspect the GOVERNOR (under $25 and not difficult to replace).

Also, how long has it been since you overhauled or replaced your AIR DRYER?

ArtJoyce · 11-18-2022, 08:30 AM

I would try the governor as others have mentioned. Freezing fog? If you have not changed your air dryer in the last year or so. It could be a moisture in the air system frozen valves.

dansawyer · 11-18-2022, 08:59 AM

Thanks for the diagnostic pointers.

Yes. i replaced the dryer about 6 months and 8000 miles ago.

I have a 110 compressor, although it is a bit small. I was able to add about 80 lbs to the system. It held and there were no obvious leaks. There is no evidence of a leak once air is in the primary tank. I cannot check the air dryer circuit itself.

Is there a check valve between the dryer and the primary tank.

I cannot find the governor. There is also a pair of wires connecting to the dryer. Is there a electrical component to the dryer?

wolfe10 · 11-18-2022, 09:06 AM

Quote:

Originally Posted by dansawyer

I cannot find the governor. There is also a pair of wires connecting to the dryer. Is there a electrical component to the dryer?

The wired to the air dryer are for a 12 VDC heater.

The governor is strictly air/no electricity. Trace the smaller air lines from either air dryer or engine-mounted air compressor and it will lead you to the governor.

153stars · 11-18-2022, 09:24 AM

EDIT.. I started post before last two posts so some overlap. I read your not hearing air dumping but purge hole is big may be muffled.
There is potential for freezing if air dryer is bad. It does have a 12v electric heater. Freezing fog conditions is usually just barely below freezing or or ground is freezing air is warmer . Have you been driving in below freezing conditions long. I don't suspect air dryer heater is the issue at near freezing temp. Air dryer purge valve can stick partially open. Can you hear it dumping air ,it shouldn't be dumping at 90psi and not continuously.

Unplanned Tourist · 11-18-2022, 09:43 AM

If your rig holds air from the 120 volt compressor, check the compressor discharge line. It runs from the compressor on the engine to the air drier. There could be a worn spot that popped, and now air is just leaking off before it can get to your system.

Another possible cause is a stuck valve on your air drier. Although you have had it serviced fairly recently, it could be faulty. Put your hand under the exhaust port on the bottom and feel if there's air coming out when you run the motor.

Worst case scenario is the coupler that drives your compressor is stripped, or the compressor itself is shot.

dansawyer · 11-18-2022, 09:50 AM

Quote:

Originally Posted by 153stars

EDIT.. I started post before last two posts so some overlap. I read your not hearing air dumping but purge hole is big may be muffled.
There is potential for freezing if air dryer is bad. It does have a 12v electric heater. Freezing fog conditions is usually just barely below freezing or or ground is freezing air is warmer . Have you been driving in below freezing conditions long. I don't suspect air dryer heater is the issue at near freezing temp. Air dryer purge valve can stick partially open. Can you hear it dumping air ,it shouldn't be dumping at 90psi and not continuously.

It has been in the 20s. It is high 20s now with a high in the mid 30s.

I do not hear any air leak anywhere. The system is holding 45 lbs for 12 hours. I have not tried adding air this AM. Is there a check valve between the primary tank and the dryer? If there is I don't know how to check the dryer for leaks, they would not be possible to hear over the engine. If there is not then the fact it is holding air should rule out a major dryer leak.

I am still on the hunt for the governor.

Thank you all.