Dishwasher stops with "wash" light flashing

[TheAggie]

We have a GE Dishwasher Model GSD4230X73WW that was here when we bought the house in 1999 from previous owners. I'm guessing the house was built in around 1982 and it may be original equipment.
We usually run it on Short Cycle and it now quits consistently (at least a dozen times now) sometime after/during the wach cycle (detergent is all gone and dishes appear clean but wet). When it quits it is always beeping and the wash light is blinking. The label on the door states that this means a Blocked Drain and that I should "Clear air gap, touch reset, then touch start". I didn't kow what and "Air Gap" was but found the manual online and as far as I can tell, we don't have an air gap. Resetting and restarting and it will get to that point and repeat again. There is no water pooled in the bottom after the dishwasher stops so something must be draining. But, it usually takes a few minutes for me to get there so maybe it is just draining to slow. What is the dishwasher sensing that is causing it to think that it is not draining? Maybe the problem is the sensor? Any ideas? I haven't pulled it or tried and type of diagnosing yet.

[LazyPup]

Up until the mid 80's dishwashers had a relatively shallow water sump and some water was always visible in the bottom after a cycle stopped. That small amount of water is intentionally left in there to insure that the motor shaft bearing seal will not dry out and crack. While that water was necessasary to the longevity of the machine, the manufacturers continually received complaints from homeowners who did not understand the purpose of that water, so the manufacturers countered my making the sumps a bit deeper and keeping the water under the bottom cover out of sight.

The actual amount of water standing in the sump is determined by how the drain line is connected. The drain line is supposed to be run up high under the cabinetry and secured in place close to the machine which forms a high loop trap to limit the amount of water that can backflow to the machine when the pump stops. It also minimizes the potential of discharge water from the sink getting back into the dishwasher and contaminating the water in the sump.

The water level in the sump is measured by a float switch. If the amount of water backflowing into the machine is too much, or if the float switch is gummed up from soap scum or debris it will signal the control system that the sump is still full and stop the timer.

First, locate the water sensing float, and lift straight up on it. It just rests on a little post on the under side and will lift right out easily. Clean the underside of the float and the push rod. (Soap scum or debris adds weight to the float causing it to sit lower in the water and causing a false reading.

Check the drain line to make sure it is connected in a high loop as close to the machine as possible.

[TheAggie]

Thanks, the explanation helped my understanding a lot but the problem isn't solved yet.

I checked the float tonight and it didn't seem to be clogged or stuck but I cleaned it anyway and restarted the diswasher and same result. It starts beeping after about 20 min. I opened it fairly soon after it started and looked and there is no standing water in the bottom (the sump entry is full but that is covered/hidden).

I guess the next step would be to test the float switch and check the wiring but I'll need to pull the dishwasher (or at least some covers) to get to that will have to wait for tomorrow. Also, I was unable to find a high loop in the drain line but the loop may be in the cabinet so I'll check for that when I pull the dishwasher. The drain line does enter the sink drain about 20" above the level it runs along the bottom of the cabinet toward the dishwasher.

Thanks again, and nice drawings. I can see from these that we definitely don't have an Air Inlet Valve and also of note is that we don't have a garbage disposal.

If you have any more suggestions, let me know.
Thanks,
Mark

P.S. I forgot to mention that I found exploded diagrams for the dishwasher at http://www.partselect.com/AdvancedMo...Num=&fkMfgID=2

[LazyPup]

If the water is standing in the machine between cycles ,check for the high loop and a clogged drain line...

if it does pump out, and refills new water at start,,the float switch is ok.

Also,,the plumbing code prohibits directly connecting a dishwasher to the drain system,,it is required to be connected by means of an indirect waste.

a garbage disposal port is an approved indirect waste. If you dont have a disposal the code requires the air admittance valve

[TheAggie]

I got a chance to try some stuff tonight.

Yes, the dishwasher seems to go through sever wash/rinse cycles before it stops and water all drains out and refills each time.

I took the bottom plate off and checked the float switch and it works fine (as you had thought since it is draining & filling).

Any idea what else it might be complaining about or how to identify more about where/when in it's cycle it is complaining? I am a software developer but I am certainly missing the days of mechanical cams where you could visually see what was going on [V].

P.S. If you open it after it starts beeping and look, all the water is drained, lots of steam comes out, and the dishes seem clean (but wet).

P.P.S. What issue is code trying to resolve with the air admittance valve when the dishwasher is connected directly to the drain?

[LazyPup]

Check to see if you have the "energy miser" switch on. During the 80's many dishwashers were built with the energy miser switch to reduce utility cost. When the switch is on, the heating element is disabled and it relys upon normal air drying of the dishes.

IN REGARDS TO THE CODE ISSUE:
Contary to public opinion, the Plumbing Codes are not building codes, they are HEALTH CODES which are enforceable by both civil and criminal penalties. It is the primary responsibility of a plumber to insure there is absolutely no cross contamination between the drainage system and the potable water supply. (In most jurisdictions the Plumbing inspector is a county health agent and he/she not only have the power to redline your job, they have the authority to order you out of a structure,order a structure condemned for human habitation or arrest you and bring criminal charges. Although it is extemely rare that they exercise those powers, you can be sure that your inspector takes his/her job very serious.)

Dishwashers, HVAC condensate drains, Home water filtration system drains, water heater T&P valve drains and commercial refrigerator drains are not permitted to be directly coupled to the building drain. They are required to be connected by means of an INDIRECT WASTE. The intent is to prevent any bacteria present in the drain from getting back into the water supply, food storage areas or sanitation equipment.

In the case of a dishwasher the indirect waste is created by either discharging into the disposal inlet port, which is open to air and ahead of the trap, or it MUST HAVE an air inlet valve and in some jurisdictions they require the inlet valve on all dishwashers even when a disposal is present. Also, if you have a disposal, the dishwasher drain is required to be connected to the disposal. It MAY NOT be connected to the drain downstream of a disposal.

The requirement to have an idirect waste is to prevent the possibility of waste water being discharged from the sink backflowing into the dishsaher sump where it would contaminate the water in the sump and later spray the contaminated water on your dishes.

It is also a very good idea to occassionaly pour a cup of household laundry bleach in the bottom of the dishwasher and let it set overnite to sanitize the sump. (laundry bleach is an approved food grade sanitizer)

[TheAggie]

Thanks for the Code info. I find it uncomfortable to follow a code if I don't understand the "why" that is behind the "what".

When looking under the dishwasher I found a service info sheet and followed the tests. The problem seems to be that the diswasher opens that drain valve and drains the water out but never realizes that the water is gone, times-out and thus the error.

The diswasher seems to use a microswitch called the "drain feedback" that is attached to the drain valve assy. to somehow detect that the water has drained but I'm not sure how. The drain switch is coupled to the drain valve so that it closes when the valve is open. I have checked the voltage across it and it is operating correctly. It seems that for this to work, something else must be intended to cause the solenoid to open when draining is complete. My guess is either there is something machanical in the drain assy that causes this or something on the power circuit board.

From what I can tell the float valve is just used for overflow protection. That is confirmed on the service info because it is called the "flood sensor" and is connected in series with the fill solenoid. It is possible that some creative intercoupling on the power board and a delay solenoid could do this but I'm not sure why they would do that so indirectly.

I guess this is another why question. At least I'm consistent.

Do you have any experience with this type of wiring?

Here is a photo of the Drain solenoid in the off (drain closed) position.

The solenoid pulls the large metal slug down which is attached to the plastic cam with a pin that sticks out (you can see it in the bottom of the curved slot in the cam). The shaft of the cam is attached to the drain valve. As the pin lowers it pushes on the thin metal arm of the microswitch (the almost horizontal line you see crossing the cam below the pin from the shiney bracket). The microswitch button is the white bump you see under the microswitch arm nect to the bracket. I have measured the voltage across the switch and it is 5V when the solenoid is off (drain valve closed) and 0V when it is on (drain valve open).

I just thought of one thing I could try to test my theory. I'll manually open the switch/solenoid during the drain cycle and see it it proceeds with out error.

P.S.
We aren't using the Energy Saver Dry. My wife doesn't like it.

Mark

[TheAggie]

Ok, more info.

Just did the test I described.

If you open the switch while it is draining, then the cycle trys to proceed normally without error. Note I said "trys". The reason it can't is because I can trip the switch easily but the valve is still held open so it can't fill. My guess was this was somehow due to hydrodynamic pressure or something from the pump. This seems correct because the valve closes if you temporarily disconnect the motor. I also tryed manually moving the drain valve to the open position while the motor is running but the drain solenoid is not activated. Same thing, the drain "sticks" open until you pause the motor. Note: Normal operation for this diswasher (from the service info sheet) seems to keep the motor running at all the times whenever the dishwasher is running.

I don't have a clear view so I can't see how the piping is arranged down in the drain/sump area to understand what is going on. Since it mostly works I have been trying to avoid pulling/dissabling too much and risking taking it totally down until I have what I need to fix it.

Mark

[LazyPup]

Measure voltage across the terminals of s switch rather than measuring terminal to ground can be a bit confusing because the results seem to be backwards. Voltage is a measurement of the difference in potential between two points.

When a switch is in the OFF position the switch contacts are open thus there is a difference of potential between the poles, which would show on the meter as the applied voltage.

When a switch is in the ON position the voltage is passing through the switch, therefore the voltage is equal on both terminals and would show on a meter as ZERO (no differnce in potential)

It is very important that the service tech understand this, otherwise when testing a live circuit one may measure the voltage across the terminals of a switch and get a zero reading, thus assuming the circuit dead, and end up receiving a serious electrical shock. (It is normally best to measure from the unknown to a known point of ground. In the case of an appliance switch, neasure the input terminal to the appliance frame to prove voltage to the switch, then measure the output side of the switch to the appliance frame to see if the voltage is passing through the switch.)

Based upon the voltage measurements listed, the microswitch in the picture is a normally open switch.

I suspect that the valve uses an internal throttling plate similar to the choke in an automobile carberatuer. When the solenoid is activated the cam comes to a midway point while the water is flowing through the valve and at the end of the pumping cycle the flow is reduced, thus allowing the solenoid to pull the cam to the full down position, which would then close the microswitch. When the microswitch closes it then passes a 5v signal to the control to advance to the next cycle.

To test the theory on your machine, while the pump is running,Do not touch the plastic cam. Try pressing down on the microswitch cam lever to see if it signals to release the solenoid.

If that proves to correct the problem, i suspect one of three problems:

1. The cam slot is dry and friction is preventing full movement. (Apply a bit of white grease in the cam slot)
2. The microswitch may be slightly out of line or the actuator control arm is slightly bent and it is not fully depressing the microswitch.
3. There may be a piece of debris inside the valve body that prevents the final motion.

there may be some debris in the valve body that is restricting the final movement.

I am posting an illustration to show the correlation between the internal function of the switch and the readings you get on a meter when measuring across the switch terminals.

[TheAggie]

Thanks Richard,

Yep, I agree that understanding what is going on with the electricity is very important (to know the why and just the how or the what). I'm pretty good at that as I have a Master's Degree in Electrical Engineering).

Did you see my follow-up post? I think I did pretty much the same test you mentioned and the control circuit responded correctly but the valve was still stuck open.

Also, the voltage I mention is across the switch (5v when the solenoid is off / valve is closed / switch is open, 0v for the reverse) so switch is normally open. That was easier to measure than back to the reference and I had clip leads so I colud hook it up while the power was off. The solenoid moves freely and the valve also closes easily, but once the valve opens it is VERY difficult to return the valve to the closed postion if the motor is still moving. Once you cut the motor off it moves freely and closes on its own by the force of the spring. So...

1) Cam slot seems OK, pin moves freely along it
2) Microswitch tests out OK. Very high restance when open and low when closed.
3) It doesn't seem like anything is clogging it because then why would it close easily when the motor stops.

I wonder if something like a piece of the impeller or something is pressing against the valve flap or something like that that is holding it open. Otherwise, there must be something that is pulling a lot of vacuum or a lot of water flow that is some how circulating and holding it open.

I may have no choice but to pull it out and open things up to find out and that may put it offline for a while since I have a day job. Maybe next saturday?

[LazyPup]

Another thought comes to mind. We both suspect that the discharge pressure of the pump is too high to allow the solenoid to pull the valve shut. This could be indicating a partial restriction in the drain line. Not enough to block the flow, but certainly enough to keep the discharge pressure from the pump to the point of the restriction high.

Try starting near the discharge side of the drain valve and work towards the sink drain connection by taking the hose in both hands and flex it, and continue on down the line to break up any potential clogs.

[TheAggie]

The culprit has been found (a TOTALLY wasted Piston & Nut Assy).

[LazyPup]

I have also found some very interesting information. If you will go to www.yahoo.com and input the model number in the search bar you will find complete parts breakdowns on the machine.