Karcher K4 electrical fault

Orson100

Hi, hopefully somebody can give me a steer on this:

I have a Karcher K4 with the following fault: Recently, the device has begun to fail to start without warning. It is relevant that this does not happen mid-wash, it happens when I release the wand trigger and then simply won't turn back on when I press it again. When this occurs, and I check the resistance between live and neutral on the plug when the Karcher's main power switch is on, it reads open-circuit (should read 5 ohms or so).

I have opened and closed the pressure washer twice at this stage, on the 2nd occasion, replacing the oil. Everything mechanical is in working order and is in good shape (washer not that old). All contacts look clean and are made well to my eye, which is evidenced by the fact that on both occasions, the act of disassembly and re-assembly has resolved the issue (before re-assembly I check the continuity between L and N on the plug again with power switch closed and it reads 5.4ohm) ... but only for a short period, problem re-surfaces after 30 or 40 minutes of use, and then only after I release and then depress the trigger again.

This is not a pressure problem, my pressure is very good, there are no leaks, the motor hums along (when it is working). This is an electrical problem. This is not a temperature issue, the housing does not get hot, and the issue does not resolve by itself as one would expect for a thermal cutout issue.

So there's the background and here's my question:

I think it must be either a faulty main switch or a faulty motor run capacitor and just wondering if anybody can tell by the failure mode which it is likely to be so as to avoid my buying a part I don't need? Can capacitors be intermittently faulty, with a resolution path of simply dis-/ re-connection only to re-present with the same issue later? I feel it is more likely to be the capacitor because if it was simply a faulty main switch then this would be amenable to failure at any point in the wash cycle but failure does not occur mid-wash, only when hose trigger is depressed. Also, one might expect that a power switch issue might be easily recreateable or identifiable.

I hope this is clear enough and somebody can advise perhaps?

TIA
Orson.

red sean

When you had the washer open, did you notice if the cooling fan on the motor was tight?
I have seen the fan come loose on a few Karchers resulting in the appliance overheating and failing to restart when the trigger is pulled, like you say. After a cooling period it would again re-start the same cycle.
A thermistor in the motor shuts it off until it resets after cooling.

Orson100

Hi red sean, thanks for the reply. The motor on the K4 does not have a cooling fan, it's cooled by the water that it pumps which is circulated around the pump enclosure.

For the record, I opened the unit for a third time, this time being careful to continuously for continuity across the L and N of my mains plug while I dis-assembled. Kind of obvious but as soon as I removed the motor run capacitor i got my 5 ohms continuity across the circuit restored. Re-inserted the capacitor, still got my 5 ohms, and when re-assembled (getting very fast at this), device worked for around 40 minutes with no issues, releasing and engaging trigger many times, but I presume it may fail again at any time.

i had been labouring under the impression that once the capacitor was gone, it was gone and machine would not work period. But apparently not it seems. I'm going to order in a spare in the expectation that the problem will recur.

Thanks again. Orson.

The Red Ace

I would suspect that the flow switch is faulty, it is activated by the flow of water and not picking up on it

brightspark

The Red Ace wrote: »

I would suspect that the flow switch is faulty, it is activated by the flow of water and not picking up on it

Not familiar with that exact model but I always thought they operated on pressure.

When the trigger is released the pressure builds and the switch turns off the motor, when the trigger is pulled this causes the pressure to drop restarting the motor.

I'd suspect the pressure switch, while a faulty capacitor could cause intermittent starting problems the OP wouldn't have an open circuit when checking the plug.

Pressure switch staying open would show an open circuit when checking the plug.

Alternatively is the wand trigger actually allowing water to flow? If for some reason the pressure was not dropping then of course the switch wouldn't allow the pump to start.