LG LDF7932 not washing properly - how to diagnose

[manoweb]

Hello, I am not an appliance professional... But as I've been through a lay-off during the pandemic, luckily my wife still has her job, at least I'm trying to fix things around the house. We always have to pre-wash dishes quite thoroughly, and especially stuff on the upper rack is never really clean. The dishwasher smells, it's not terrible, but I don't think it should be like that.

It is a LG LDF7932, nice good looking unit in stainless steel. In the past they changed the whole pump/motor assembly because it was very noisy and I believe it actually stopped working, but I do not remember much about it.

This time around, money is a little scarce and I'm trying to fix it myself if I can, I hope it's just some maintenance and not an expensive fix. What I did so far:

1. make sure it's perfectly level and correctly fixed to the cabinets. In fact it was all crooked, I even replaced the side "ropes" that were almost completely frayed. However, it did not improve much
2. I opened up the pump assembly/filter and cleaned it. There wasn't much, but definitely something that looked like wet paper, like a label from a jar. I also noticed a small rubber valve was only half there so I put in a new one (it should be the check valve for the drain)
3. I removed all the internal water ducts and washing arms and cleaned them. I did remove some more of the "wet paper" material; at this point I was quite sure I'd fixed it but... not really. It's improved, especially the bottom, but the upper rack is still not good.
4. Yes I ran a hot "sanitary" cycle with a cup of white vinegar in the upper rack like every website recommends - no improvement, odor is still there, upper rack does not wash well.

This evening I tried to open the dishwasher in the middle of a cycle and I never saw the upper arm spinning. It feels like there isn't much pressure. I set it to a specific position and it never moves from there. The mid arm however seems to spin; in fact I even bypassed the door lock to see stuff running but I can't do that for too long before I flood the whole kitchen. I have seen the bottom arm spray with pretty good pressure; the mid and top arms are trickling some water at the same time, which I am not sure should be happening. I was never able to see the mid and top spinning because I guess that comes later in the cycle. Note the drain pump works well and also the inlet valve seems to fill promptly. Earlier this evening I tried to interpret the service manual "test mode" and go through the tests. I am not sure I understand all of them but I wasn't able to make the top arm spin. That might be due to the fact I don't know what I am doing.
What is that I should do next? Thank you

[john63]

This is the first generation LG dishwasher.

Known for Wash Motors degrading (water contamination).

The wash motor is located at the bottom of the Sump...the *only* thing keeping water from destroying the motor...is a tiny o-ring.

New model LG dishwashers have the Wash Motor mounted 12 o'clock position within the sump assy.

The Wash Motor *can* be replaced...but the o-ring is not available. Pointless.

To correctly restore proper cleaning...it will be necessary to replace the Sump Assembly.

Depending on the build date (Serial Number) there are a number of other achilles heels with this design/model. Best to buy a new dishwasher.

Edited July 25, 2020 by john63

[manoweb]

But as I said, the motor/pump assembly was changed few years ago, the unit at the very bottom. You are saying even the replacement has the same issue and therefore needs to be changed again? That might be the case but why the bottom arm seem to have good pressure and cleans decently?

[john63]

Yes.

That design is prone early failure.

Wash Motor slowing down...cannot sufficiently pressurize middle and upper wash arms.

Guide/Float Assy also known for issues...

Depending on build date...the thermal wrap may damage wiring inside the door.

 

[manoweb]

I checked and the whole assembly sump/motor/filter assembly is about 200 dollars. Swapping it out seems easy enough. As money is kind of tight right now, do you think it is not a good idea t replace that only? I understand a new motor is also going to wear out in a few years because of the design, but I just cannot get a whole new dishwasher right now, we'll have to continue washing by hand...

[john63]

No harm in doing that...

With the dishwasher removed...inspect the Float Assy on the left side of the dishwasher.

If heavily contaminated...it can be removed and cleaned.

What is the Serial Number?

[manoweb]

Thanks;

S/No: 102KWAT00248

Model: LDF7932ST

[manoweb]

In the meanwhile I decided to pull the dishwasher out completely and perform the inspection that you have recommended. It seems in a pretty good condition - am I looking at the right thing?:

 

[manoweb]

However, the bottom panel definitely shows signs of rust:

This is the sump/motor section:

Honestly the motor does not seem in bad condition...:

 

But the little valve motor is probably shot:

Do you think it might just be the vario motor?

[manoweb]

I have made another test removing the internal water guide and arms and the dishwasher is always pumping from both lower and upper at the same time. Is this what is supposed to happen? I thought the dishwasher would use the "vario" or "diverter" valve to select upper or lower, not both. This could explain the low pressure on the top washing arm

[manoweb]

I have found the vario (diverter) motor had a problem with the wiring. I now checked it and I moved the dishwasher to the deck, bypassed the door lock and tried a test rinse cycle. Now I see the water being pumped alternating between the upper and lower arms.

 

[manoweb]

This is the inside of the old "vario" or "diverter" motor:

[manoweb]

Some automotive polish (3-stage) with a Dual Action Porter Cable and the stainless steel looks as good as the day it was installed. I really hope my wife will find it acceptable