Random Electrical Discharge [A/S 325]

[Fish36991]

Thanks Beginnner,

Trip has been moved up to this weekend, I'll be flying out tomorrow to the location of the airstream. I'll try this out and let everyone know how it goes and what I find. I've set aside several days to troubleshoot it. Already spoke to the Alternator/starter shop and will be ordering very soon....thanks for the info on that one.

Also, anyone know where to pick up the high current isolator?

Beginner, I was thinking...correct me if I'm wrong. I should also be able to find the bad circuit by placing the meter in parallel with each breaker. When the breaker is in the on (normal) position, no current will flow through the meter because through the breaker will be the path of least resistance. When the breaker kicks open, the current will then flow through the meter and register on the display. Since you have to read current in series with the circuit, the breaker would create the open for you and allow all current to flow through the meter. Second thought, that may blow the fuse in the meter. But, I would trade a fuse to make sure I had the right circuit. Just a thought.....anyway, maybe the light bulb is the better way to go.

Thanks again, I'll be offline tomorrow around 2PM EST so anything you guys can think of between now and then, post away.

Thanks to everyone...I don't know for sure but this has to be the best airstream forum on the net!

Josh

[Beginner]

Symantics. The term I used "across" meant in parallel. A volt meter has very high internal resistance. Ths minimum internal resistance that I have run into is 20,000 ohms. At that resistance only .0006 amps (.6 milliamps or mills) will be allowed to flow through the volt meter. If you have a digital multimeter the internal resistance is higher. My Fluke 87 runs about 1 million ohms which will allow only 0.000012 amps (.012 mills) to flow. Now if you select amps on your multimeter, I promise you that you will blow the internal fuse as most are capable of carring only 10 amps. The circuit breaker that is making and breaking is rated at 30 amps.
The low voltage that you will be reading when the breaker is "made" is the voltage developed across the contacts. It will hopefully be less that 1 volt or the contacts are damaged. Usually when 10 amps at 12 volts is conducted across a set of contacts you will get at most a few millivolts. This voltage which is developed across the contacts at a known current is the only easy was to calculate the point contact resistance of the contacts because the resistance is to low to be accurately measured by even a good multimeter.
First I learned the correct way to measure things (electrical). Then on that Sunday night, forty miles from nowhere with no tools I figured out methods of troubleshooting with no handy dandy test equipment.
Any way, when you determinewhich breaker is making (on or closed) and breaking (off or open) you will be well on your way. Follow the wire, start disconnecting the items fed by that wire.
If you use the light bulb, connect one side of the bulb to the + terminal of the battery and the other side of the wire that you have just removed from the circuit breaker(load). The light should come on. When you remove the appliance that is shorted or drawing too much current, the light should dim or maybe even go out.
Measure voltage between the - post of the bttery and the disconnected wire. It must be 0 to prevent damaging your meter. With the meter set on RX1, connect one lead to ground (- post on battery or the metal framd of the vehicle) and the other end to the disconnected wire. You should get a low resistance value. When you disconnect the offending appliance, the resistance should increse dramatically.
Good Luck/Good Hunting
Let me know what you find.

[ALANSD]

The isolator I bought off Ebay. It was new and unused. There are many available online.
Mine is the same brand as my old one, (which I then sold on Ebay) a Surepower I think.
Ended up with a new more powerful one for very little outlay.
The ones at the auto parts stores are too low rated.

[Fish36991]

Guys,
First off thanks for all the help. I found the problem in about an hour and a half but the crazy part is it wasn't anywhere I thought it would be. But here's the update as promised.

It definitely was a 30A breaker that was clicking and in 30 second intervals which is exactly the amount of time ya'll said it would take to reset. I replaced all threee breakers under the hood that feed the three main circuits after the isolator (isolator checked out good by the way as well as the alternator). I have a Fluke 83 and I knew it could measure over 10A for a short time anyway before I blew my fuse...so I measured it. It measured 39A when the 30A breaker would open so I knew I was in the right place....one fuse down. Replaced fuse (I planned for this). Went through the schematics and three things run off this particular fuse: Driver side power seat, Passenger side power seat, and the Air Ride System. The driver side seat is screwed up and I just knew that would be the problem so I disconnected it...problem remained. Disconnected the passenger seat....problem remained. This left the air ride system so I disconnected the air ride system and reconnected the seats and it was fine...even when moving both seats. Measured the current through the air system with the meter...definitely the problem...second fuse down. Replaced fuse.....again.

Air Ride System:
The strange thing about this system is it was running sometimes and others it wasn't. I pulled the schematics for this and read the theory of operation...simple enough. Verified a good ground before going any farther... verified good. Disconnected the three wires running to the pump itself (two grounds and one hot 12VDC). Reconnected and the problem was gone so I thought the pump was going out and pulling WAY too much current but I wanted to verify the rest of the circuit while I was there so I did. Verified the 12VDC directly from the breaker under the hood (good). Verified the 12VDC coming in from the ignition when the key is turned to the main relay (good). Made sure the relay was switching over to turn the pump on and the correct voltages were being applied to the pump connections (good). Verified the low pressure switch operation (good). That covered the entire system except the pump so I used jumper cables to a battery to fire off the pump. I would turn and pump air but you could tell it wasn't smooth and or consistant like it should be...you could hear it's RPMs go up and down. Connected the meter in series to the pump to measure current....problem found...third fuse down. Replaced fuse.

We pulled the pump and he's ordering an replacement today from and airstream dealer in TN so that should get him back on the road. He was also very happy with how solid the voltmeter on the dash was without the random loading going on. The Airstream should be back on the road 100% by the end of the week.

I know I went into alot of detail but maybe it will help someone else. Thanks for everyones help!

Josh

[87MH]

Originally Posted by Fish36991

...would turn and pump air but you could tell it wasn't smooth and or consistant like it should be...you could hear it's RPMs go up and down. Connected the meter in series to the pump to measure current....problem found...third fuse down. Replaced fuse.

We pulled the pump and he's ordering an replacement today from and airstream dealer in TN so that should get him back on the road....

Josh:

It may well be the pump, but consider one other thing....

there is a back pressure valve (check valve) on the top of the volume tank..
the pressure sensor for the high pressure shut off for these units comes off of the tank....downstream of the check valve.

The check valves are pretty close tolerance and have been known to "gunk up". The valves are common and most parts stores have them for a few bucks.

If the problem persists after installation of a new air compressor I would suggest replacing the check valve - it could be that the valve is plugged up and the compressor is choking due to high pressure on the outlet side -
in other words, with the back pressure (check valve) plugged off, the compressor is discharging against a closed system.

Even in normal operation these compressors draw a fairly high amperage load - and the wire going to them is marginal at best (10 guage originally on my 345 - and it is a LONG way from the front breaker to the compressor at the back) - just a slight increase in the "normal" amp load could possibly cause the compressor feed wire to heat up, increase resistance, and attempt to draw even more amps - just a thought.

Don't forget there is a separate "blow down valve" that relieves pressure from the compressor discharge when the compressor is not running - and is activated (closes the blowdown valve) when the compressor is running. This solenoid could also have a short in it, causing your high amperage condition.

Luck.

[Fish36991]

You're killing me....Just when I was sure I was done, I'll have to have him check it out but I'd rather know now than fight it later. Thanks for the input....also, where is this selenoid you're referring to? I may have to walk him through it over the phone to check it out. thanks,


Josh

[87MH]

Originally Posted by Fish36991

You're killing me........also, where is this selenoid you're referring to?

Here is a pic of my system - your's may be a bit different -

The "Bleed down Solenoid" is mounted on the accessory rack, in the picture, just to the right of the pressure control (on - off) switch -

[Fish36991]

87MH,
OK man...you're good. He received a quote to replace the pump and they Airstream told him a little over $600 and I told him about the check valve. So, with the price of the pump in hand, it remotivated him to verify the check valve....and....it was bad. So, he spent $15.00 for the new valve and put it all back in. They Airstream is doing great and he's very happy.

He wanted me to tell everyone on here thanks and how much he appreicates all the help. I bet he wishes he used his computer more and would upgrade from dial up now!

He just needs to fix his speedometer and he'll be 100% back up and running. Thanks again guys. I'm going to keep this thread bookmarked and I'll post any updates that come along. I can't offer anyone any advice but I don't want to just "eat and run". I feel like we've bonded... ha

THANKS!!!!!!
Josh