Troubleshooting FW Tank Sensors

[chasfm11]

While sanitizing our fresh water tank, I noticed that only the tank full sensor appears to be working. While I realize that sensors aren't very accurate to start with, I thought that I'd take a crack at trying to determine why the 1/3 and 2/3 sensor lights don't come on for this tank.

I started by taking the panel off of the wall, looking for manufacturer information and to see the wiring. There is no sign of a maker or model on the panel itself. In addition, I was expecting 9 wires (3 from each of the tanks) besides wiring for the other things that the panel controls. No such luck. I double checked and there was nothing about the tank sensors among my manuals. Here is what I know.

- the panel has leds for fresh, gray and black tanks as well as for the house batteries. It also has water heater and water pump switches.
- there is a circuit board behind the panel with a plug containing some wires. There are much larger wires, which I assume drive the switches.

I spent a lot of time troubleshooting main frame computers for a living so with a diagram or an overview of how things are supposed to work, I can generally figure it out I assume, since all of the tank sensors are apparently not wired to the panel that it is some sort of a progressive resistance setup like resistors in the blower motor in a car.

Any ideas about who the manufacturer is of my tank sensor kit or about how it is supposed to work are greatly appreciated.

Charlie

[Darrel]

For what it's worth I had a similar setup in a 2000 Allegro Bay Pusher. I once removed the panel covering the holding tanks and found that the three wires from the sensors were routed into a round module and a single wire then led to the monitor panel. I assumed that the round module was a sort to variable resistor that determined how many sensors were wet. I have to admit that the setup didn't work very well for me either.

Have a nice day - Darrel

[Bob (WA0MQE)]

Doesn't it make you wonder why with technology as advanced as it is, the manufacturer's still use the cheapest, and poorest design for this function. We can upgrade our systems ourselves with after market systems that are a 1000 times better, but with a hefty price on our part. You'd think all the manufactures would utilize these newer systems. Purchasing in quantity would surely cause the price to drop to a something more reasonable.

[DAN L]

Originally Posted by chasfm11

While sanitizing our fresh water tank, I noticed that only the tank full sensor appears to be working. While I realize that sensors aren't very accurate to start with, I thought that I'd take a crack at trying to determine why the 1/3 and 2/3 sensor lights don't come on for this tank.





Charlie

my fresh water tank holds 80 gal.
i added 1 gallon of cheap vinegar to the tank and filled it. i let it sit for 48 hours, then drained and flushed it twice. the full tank and 2/3 tank lights work ok now. when the 2/3 light goes off, my tank has approx. 20 gallons left in it and reads empty.
next time, i am going to use 3 gallons of vinegar and drive the moho around with the solution in the tank.
before you do this, turn off your water filter supply valve if you have one.

[RV Wizard]

Charlie, you probably have a KIB sensor and monitor system. I would recommend checking the connections on the tank. If they are good try changing the grey tank (if working) over to the fresh tank to verify monitor. If it looks like all connections are good most likely the culprit will be the the resistor pack and sensor leads. Good luck and keep us posted.

[chasfm11]

Thanks for the great information, Mike. My FW tank is very enclosed so I'm going to have to start by just figuring out how to find the sensors and resistor pack. I looked at the KIB website but their panels don't seem very close to what I have. Would a picture of mine help?

Assuming that it is the resistor pack, do you have any ideas about a source for it? I've done some searching through the RV parts suppliers and there isn't much of a hint online that there are such things available. I do recognize that they probably don't put their full parts line on their Web sites. I looked at the KIB Web site but they only provide an order form. I would guess that calling them would be the best to verify that I was ordering a part for the correct model, assuming that mine is one of theirs

I had, for a short period, considered going to a system like SeeLevel II. The problem is that my gray and black tanks are about 6 inches by 3 feet by nearly the width of the RV and are installed on a slope. I'd want to talk to someone at Garnett to verify that their sensor system would be as accurate in my situation as they claim. Model 709 PH is exactly what I would need. It would be interesting to find out if the LP sensor would do a better job than the gauge that I have on that tank today.

[RV Wizard]

Charlie, you should be able to look closely at the printed circuit board for some information on the manufacturer. A photo may help to identify them as well. More than likely you will have to drop the belly pan to access the fresh water tank.

[Clay L]

If it's made by Ventline as many are, there is a 68k ohm resistor between the full and 2/3 sensor and one from the 2/3 sensor to the 1/3 sensor. There is no resistor between the 1/3 sensor and the ground sensor.The wire from the display panel connects to the full sensor. On some units the resistors are potted in a small plastic cap close by the tank with one wire leading from it back to the panel. There is another wire from the ground sensor also going back to the panel.

On others all four wires go into the wiring harness and I don't know where the resistors are located. Maybe on the display panel?

The display panel has five "LM339 Low Power Low Offset Voltage Quad Comparator" ICs (one for each waste tank, one for the propane tank, the water tank and one for the battery voltage) that are used to sense the voltage drops across the sensors and activate the proper LED.

Since the full LED works, I doubt if the problem is the resistor pack. I would suspect the the fresh water LM339 IC .

[chasfm11]

Clay, thanks for the great input. I suspect that you are are correct about my setup because the panel has a harness with 4 tiny wires. I don't have an LP indicator but the wiring may be universal. In the failing condition, all of the LEDS come on when the tank is full, not just the top one. But some sort of sensing failure in the IC makes sense.

Now that I have a good idea about how it is wired, I might pull the bottom cover on the tank and take a look.. It would be great if one of the resistors was loose.

Thanks again for your input.

Charlie

[Hooligan]

Hi Charles: I found this link, hope it helps.

http://www.afnash.com/downloads/uplo...r%20manual.pdf

[chasfm11]

Thanks, Hooligan. I read through the information in the document but there were no revelations except for their statement that the fresh water tank problems are apparently more than surface probes - they actually project inside the tank. One of their other statments is that I need the specific wiring diagram for my model system before I start troubleshooting (duh!)

I've sent them an e-mail with a detailed description of my panel. I looked at what I'm going to have to do to access the FW tank and it looks like a real PITA. There is no way that I want to go through that if Clay's idea about the monitor panel IC failure is correct. I'll see what they have to say. For all I know, however, they are one of the companies that is now belly up because of the economic downturn. It did appear from their website that they have other business lines besides RVs so I'm somewhat optimistic about a response.

You are a great help to me as always.

Charlie

[John-D]

There are basically two types of tank sensors.. The standard, and a collection of things like See-Level which I'll call DELUX. If you have a DELUX sensor.. Stop reading this post NOW cause this applies to standard

I will use a system with 3 levels

Full, 2/3 and 1/2

The system, greatly simplified, looks like this

Battery----Panel----Full--/\/\/\--2/3--\/\/\/--2/3 Ground----chassis

(Note there is a ground lead on the chassis too)

Your tank has 4 "sensors" (one more than the number of lights)

One on the bottom is the Ground, next to or above it is the 1/3, then the 2/3 then near the top is the FULL

These "Sensors" are nothing more than screws or nails or pins that go through the plastic of the tank and into the water.

Water (Unless it is lab-grade pure) conducts water (Yes, I've worked with lab grade pure and no it did not conduct) Well water is NEVER that good.

IF the sensor is under water... It is connected to the "Ground" sensor

So, to test

Take a jumper wire.. Hook to the "Ground" sensor with one end, then while your partner reads the indicator touch it to each of the other 3 sensors, if your partner can not tell you which sensor you are touching, you have a problem

The complex system (part of)

I show a sensor, then a resistor, then a sensor then a reaistor then a sensor

Both of the resistors are encased in eqoxy, there is an epoxy chip with five wires going in/out of it. IF the wire from this chip to a sensor is broken, the sensor won't work

IF one of the resistors inside the chip is burned out, then .......

Depending on which one

Either the 1/2 or the 1/2 and 2/3 sensors will not work

Humm.. you have 2 non-working sensors

The CHIP may (should be) called the "Sensor Resistor Assembly" and I'd be offended if I did not get change back from a ten spot being as there is about $1.00 worth of electronics in that chip

[Hooligan]

Charles: I have the 3601 model Landau, I have 60 gals of FW in 2 -30gl tanks. My tanks are easily accessed through the storage compartments on the passenger side, behind carpeted panels. I completely removed the forward tank at one time to paint and seal that compartment. I put a lexan window in the panel for the aft tank to see the water level. (I had a problem with siphononing until corrected by the dealer)
If you have the 3602 model, (2 slides) and 90gl FW I have no idea how to get to it.
Only the aft tank, above the pass-through compartment has the probes attached. The probes are the same as on the waste tanks (Buttons with a screw)
The wiring: (Tank empty, wires connected, resistance to ground)
Bottom wire, WHITE, zero ohms, next above is blue at 280k, then yellow 135k and the top sensor, Green and a white/brown stripe, measures 88k. The blue, yellow and green wires go only to an epoxy capsule (1/2x34") next to the tank. Only the white wire and the white/brown wire go into the harness for the panel.
The waste tanks have the same wiring, even the white/brown stripe wire is the same. I thought this wire would be color coded.
Again I hope this helps..

[chasfm11]

Wow! You guys are terrific. Yes, Hooligan, mine is a 3601, the same as yours. I never would have tried going in through the panel on the passenger side because it didn't look like that back panel was easy to remove. I was going to try the bottom.

Assuming that I get good weather this coming Saturday, I'm going to tackle this project. Armed with the correct information (as I know am), I should have no problems.

John, my system is not a Delux but I've questioned Garnet Technologies about the applicability of their Model 709-PH to my configuration. I've learned that they have a site in Granbury, TX, not to far from us. If my work on the existing tank sensors yields a less than satisfactory result, I may order the SeeLevel version and simply upgrade my situation. Now that I know how to get to the side of the FW tank easily, figuring out the sensor configuration for the SeeLevel system is much easier.

I'll post my results as soon as I get them.

Thanks again.

Charlie