Onan 3600lp turns propane regulator to red

here is the problem



I purchased two lines that screw in to the inside threads of the propane tank and have no flow limiting valve.

Well I installed the unit in to the RV yesterday. Got everything hooked up, bolted down and wired in. Made sure the demand regulator opened properly by hitting the prime switch and blowing a little on the vent hose. Cranked and started right up......... and then promptly sent the RV propane regulator to red and shut down. I about cried. I went through the whole process in my head. It ran just fine in the garage, what had changed. Through process of elimination I determined it was the pigtail hose. NRALIFR nailed it again. I never suspected the pigtail hose because in theory that would only effect the propane flow from one tank, not both. If the pigtail was bad on one side the flow would be fine from the other side, but both sides produced the same results. I had a long pigtail made a couple years ago so I could bring a separate larger propane tank with me on long stays. I had the original pigtail that I used with my temporary set up in the garage. The original pigtail worked fine. So, I still believe the demand regulator was not working right because the generator did not run even with the good pigtail until I rebuilt the demand regulator. It was a combination of things, both pigtails and the demand regulator. I don't know how all that could have happened unless it was caused by the same event. 99% of the time I get my propane from a large supplier here in town. I don't use gas stations or U-haul or what ever. I don't think I got bad propane, and even if I did get one tank of bad propane, how would it effect the other side pigtail? I really don't understand how it could have all happened at the same time, but it did. Anyway, thought I would follow up with that news. Going down to the propane supply house today to replace those lines. Thanks for all the help!

MrWizard wrote:
let us know, how it runs after install

You know, that's a good point. I had lost track of the fact that the generator had been removed from the camper. And, to be honest, I can't explain how the demand regulator was causing the auto-switchover regulator at the LP tanks to turn red.

Caribou, if the LP regulator at the tanks still turns red after re-installing the generator, the problem has got to be either the pigtails between the tanks and the regulator, or the regulator itself.

The pigtails have a device called an "excess-flow check valve" included in the green plastic nut you connect to the tanks (called an ACME nut). The purpose of the check valve is to detect a broken LP line, and to then shut the flow of gas down to a very low amount. It doesn't shut the flow off completely like a normal check-valve would though, and that can cause some confusion. Typically when the check valve goes into "flow limiting" mode, the flow will still be enough that a stove burner will work, the fridge will work, the furnace MIGHT work (or at least work for a while), but the generator will starve for fuel.

The amount of flow it takes to trip the check-valve is determined by the color of the ACME nut. Besides green, there are also black and red nuts. The check-valves can fail and refuse to open up to full flow, and they can also be "fooled" into thinking there is a leak if you open the valves on the tanks too quickly, and go into flow-limiting mode. That can happen if the camper has been sitting unused for a while with the LP valves closed, and over time all the pressure in the lines has bled off.

The auto-switchover regulator may also be able to fail in a way that regardless of which tank is used, the amount of flow will be insufficient. I've never personally had one fail that way, but I've replaced both the pigtails and the auto-switchover regulator on my campers for other problems.

Hopefully, you put it back in the camper and everything is fine. But if not, don't panic. Sometimes you fix a problem by eliminating what it isn't.

:):)

Congrats on the Fix
and thanks for posting back
let us know, how it runs after install

I agree, the demand regulator must be a finicky system because there was absolutely no indication mine was bad. The diaphragm had no holes, the valve seat seemed to close and open properly and the troubleshooting test per the service manual did not indicate any problems. Obviously the diaphragm wears out to some degree which makes sense since it is a flexible sheet of material and in my case is about 10 years old sitting in a very dry climate.

I have the prime option on my unit also, but like yours all it does is open the electronic shut off valve and allow flow to the demand regulator. I suppose a simple prime would be to blow slightly in to the demand regulator vent tube while holding the prime button. That would open the demand regulator and allow flow to the carburetor.

Thanks for the pat on the back, I feel pretty good about getting it fixed.

Thank you so much for posting that update.

The purpose and operation of the demand regulator on LP fueled generators is widely misunderstood, including by me until I had problems with the one on my Generac. I'm convinced that it is responsible for some of the bad reputation Generac LP generators have amongst RV'ers, and the premature abandonment of units that could have been cheaply fixed.

I would encourage all LP generator owners (if at all possible) to replace their demand regulator with one that has either a manual or electric prime capability. The reason for this is simple: it gives you the ability to manually open the regulator as a trouble-shooting aid. It also makes the generator easier to start after sitting idle for days or weeks.

On your Onan, it may take some modification of the generator in order to take advantage of a demand regulator with priming capability. Since you indicate there is a problem with clearance on your unit, you might have to add a switch to open the LP shutoff valve, and another switch to operate the prime solenoid on the demand regulator.

My Generac already had a switch labeled "Prime" that opened the LP shutoff valve, but since the demand regulator had no prime button on it, the LP would only flow to the closed regulator and stop. There was no way it could truly prime the engine. After replacing my regulator with one that has a manual prime button, I can press the Prime switch, then manually operate the prime button on the regulator for a second or two. That's all it takes for the engine to be primed, and it will start up after a very short crank. No more grinding the starter for what seemed like an eternity.

Congratulations on fixing it yourself, and undoubtedly saving a ton of money in the process.

Thanks again for posting the resolution.

:):)

This is great info, glad you got it fixed!! Thanks for posting back too....I have done similar research on other issues, only to find the guy that posted the identical problem to mine never posted back to say whether he got it fixed or not....

I received the demand regulator rebuild kit yesterday. It contained more parts then I needed because it is used for several different versions of the 52N regulator, but it had the parts I needed. Basically I changed out the shut off seat, the shut off valve, the spring and the diaphragm. I put it all back together and she started right up and ran smooth.

I can't really say what might have been wrong with the old regulator, but I imagine the diaphragm wears out and somehow either allows too much or too little fuel flow to the carburetor. I did not hook up any load to the system yet but once the generator started the circuit board seemed to take over and run the throttle plate normally. I'm going to get it installed back in the rv this weekend.

The frustrating part of this was the complete lack of information on the troubleshooting. If I had gone by the Onan tech manual I would have replaced the circuit board before I suspected the demand regulator. I would have taken the whole brush assembly apart and performed other unnecessary tests. The tech manual clearly says the demand regulator is rarely the problem and all other troubleshooting steps should be performed before replacing the demand regulator, right. The test of the demand regulator only tells if it opens or not, it does not test for fuel flow. I found one thread on the web that documented this problem in another forum. The guy did all the tests I had done and he finally ordered a new demand regulator and then let the thread go stale and never said whether it worked or not. Any way, I'm glad it finally seems to have been fixed.

Finally found a repair kit for a decent price

http://www.centuryfuelproducts.com/parts/repair-kits/52b-rbk-repair-kit.html

I believe this will work for my regulator. This is a repair kit for a regulator with a primer, which mine does not have, but I believe the main diaphragm is the same for either model. For $25 I will take the chance.

I read a lot more over the weekend. Had to do the glow plugs on my diesel, so I didn't spend much time on the generator. I borrowed good compression gauge from a friend because mine is pretty old and beat up. The compression test with his gauge read 150 lbs, so I know the engine is good. I wish I could find a rebuild kit for this demand regulator.

The test with the manometer between the demand regulator and the carburetor should measure a slightly negative pressure. This is due to the vacuum of the piston pulling the fuel in the the cylinder. I still haven't done that yet.