We have a Kenmore 110.28082700 washing machine that I've done a lot of work on over the years. These seem to be famous for getting an "LF" long-fill error. Well, we started getting that again, and after a good deal of fooling around and false starts, the problem came down to valves operating at the wrong time. I STILL have no idea why, but I know what it isn't.
There's a pressure sensor used to detect water level. I took it off the board and tested it, and it appears to work as desired. it has a part number that doesn't match anything on Digi-Key, but it is clearly an NXM sensor similar to a bunch of models Digi-Key does carry, and that was enough to be able to power it and test it.
The design of the water valves is this: There is a hot and a cold inlet valve, and a thermistor. Then, this goes to a manifold with 4 valves. It can dispense directly into the basket, and this works fine at a fast flow. Or, it can dispense into the detergent cup, the softener cup or the bleach cup, to send those solutions into the wash. These run very slow, so as not to overflow the cups.
So, what we see is the basket fills for a while with the direct valve, then that shuts off, and it fills the rest of the required water level from the detergent cup, ONLY. This takes so long (it can take up to 45 MINUTES!!) that the machine stops with the LF error several times before it gets to the washing stage. I can see why it turns on the detergent valve, to add the detergent to the load, but I do NOT see why it shuts off the direct fill valve. After trying many tests, replacing the relay for the direct fill valve, etc. and not fixing it, I finally kludged it. I tied a wire from the detergent valve to the direct valve so that when EITHER relay is turned on, it will open both valves. I can't really see a downside to this hack, and it seems to have solved the problem.
The controller board is $264, and has a VFD for the basket spin/agitate motor, the pressure sensor and a whole raft of relays to control the two pumps, 6 valves, heater and door lock. One other relay failed before, and I replaced that with an SSR. So, I really don't want to replace the thing if I don't have to. The only things I can come up with that could cause this behavior are:
- defect in the microprocessor (seems unlikely)
- defect in the relay driver chip (I'm guesing it is some house-labeled Allegro chip) that causes it to shut down the relay output after several minutes.
- intermittent connection in the wiring to the valve The relay has been replaced, and I now have accumulated 3 sets of the valve manifold assembly trying to keep this machine working. So, it isn't a defective solenoid coil or valve. (They all fail the same way.)
Anyway, the machine seems to be back working at a reasonable speed per load without having to keep checking if it stopped.