Tank Gauges

[tschat]

I have had my first AS for 5 weeks now. Luckily my issues to this point have been simple. Now I am trying to fix the tank gauges. The potable tank reads correct, but the grey/black gauges are bottomed out (independant of the level). I don't think they are working correctly. How do I debug them?

-thomas

[azflycaster]

Thomas,
Here is how the gauges work (in my 75), when you flip the switch for a tank it send power to a sensor harness for that tank. The tank has several sensors at different heights in the tank. Each one of these sensors has a different resistor connected to it. The amount of power returned to the gauge is dependent on which sensors are covered.

I would start with the switch and make sure it has power. Then see if any is being returned to the gauge. Is it possible that the tanks were replaced and have no sensors or the sensors were not attached at the harness?

The gauges on mine work ok most of the time, but are not that accurate. When you see water in the shower, the grey tank is full. When you see... , the black tannk is full

[nickcrowhurst]

Originally Posted by tschat

How do I debug them?

Thomas, the indicators on my Excella are different to those described by azflycaster. On mine, when the switch is held down, twelve volt power passes down a wire to a sensor at the bottom of the tank. To indicate the level, there are a series of sensors at empty, 1/4, 1/2, 3/4 and full levels in the side of the tank near the dump valves. These sensors are just electrical grounds, and each one has an attached wire that leads back to an indicator light in the control panel. When fluid completes the circuit between the live sensor and one of the indicator ground sensors, the relevant light illuminates. You can see why all the lights illuminate when the tank is full, and, for example, just the E, 1/4 and 1/2 will illuminate when the tank is half-full. To debug, you need to ensure that power is reaching the live sensor, that the sensor ground returns have continuity, and that the bulbs in the control panel are not defective. You will need to know the color coding for the circuits. The Airstream Manual for my trailer has a wiring diagram with color codes for the control panel and tank monitor system, and has several pages of de-bugging procedures. It is very good. If you do not have a manual, I recommend you obtain one. It is invaluable. Copies are available as described by Janet at http://www.airforums.com/forums/229490-post2.html
Nick.

[Zeppelinium]

I need to recreate the control panel end of this system, the early 70s version with the four sensor wires (the sensors are just screws that poke into the tank and make contact with the water). I was thinking of doing it with CMOS versions of the 7400 series logic chips and LEDs for indicators. Anyone out there done this yet? It would be nice if you could turn it on and it would flash the proper LED (just one, not the current level and all those below that level) every 5 secs or so. And green, yellow, red LEDs, too...

If anyone has a spare "roundtoit" I'll do it.

[tschat]

I have 2 wires going from the panel to the tank. One is switched power, the other is the wire that goes to the gauge. When I go back to the tank, I have 4 wires. The switched power wire goes to the bottom "plug" on the tank. The other 3 wires go to higher "plugs" on the tank. These 3 are connected together and connected to the "sensor" wire. I get the 12v back at the tank, but still nothing on the gauges.

-thomas

[azflycaster]

Here is what the book says to do-->
1. Disconnect the connector at the tank
2. Place a 2.2 K ohm resistor across the connector
3. Test the tank level
It should read full or be ajusted to full (screw under gauge)
If it is ok or adjusts ok, the pannel is good and the sensors may need to be cleaned or replaced.