Cleaning concrete dust from fan blades in A/C unit

[Bertie78]

Lat year I bought a used portable A/C unit but realised when I got it home that it had been used in a building environment and had taken in a lot of concrete dust. I opened the unit up and cleaned a lot of the conrete dust from anywhere I could access, but it is very difficult to remove it from the fan blades. Hence when I used the unit after cleaning it continued to generate a smell and when I opened it again this year I found there was a fine layer of dust on the inside of the plastic unit - although not half as bad as it was the last time.

Anyway, I have attached a couple of photos. On one side I can get good access to the fan, but on the other the motor is in the way which gives me a tiny amount of access - maybe an inch on either side of the motor.

Does anyone know what would most effectively clean this off the fan blades?

I have seen recommendation for isopropyl alcohol 99%, but there are also specialised concrete cleaning fluids that claim to dissolve concrete like "belle clean". I have the added joy that I don't want to use any acid that might harm the fan, and I need to make sure I don't damage the motor or the shaft that is goes through one side of the fan and is bolted to the other side in the photo.

Also, if anyone knows what kind of cleaning brush works well that would help. Are the flexible radiator brushes any good?

 

[Burnerman]

Personally I'd befriend my local garage and get in there with a huge blast of compressed air from their air line......liquids are all very well when cleaning individual parts, but not as an assembly.
John

 

[Bertie78]

It's a good idea. The thing is I am not going to hike the unit there as I have no car. If I start to take it apart to get to the fan blades I have the trouble of dismantling and detaching the motor, the shaft, the plastic casing and the screws that attach the unit to the body. I could probably manage it, but it would be a nightmare. I managed to change the bearings on a washing machine a few years back, but these big jobs don't come naturally to me.

 

[JohnD]

you can probably get it off with a soft paintbrush, warm water and WUL, and a small garden sprayer to rinse it away. You need to position and tilt it so the dirty water will run out of the machine and not into moving or electrical parts.

The machines I've used had dust filters in them, is there not the possibility to put a filter sheet on the inlet side?

 

[unclebob1]

Try a can or two of compressed air? the type you get to clean keyboards etc?

 

[Bertie78]

Thanks for the suggestions. Washing up liquid didn't have much of an effect when I tried it a few days ago. I can try compressed air, but I suspect it will be the same. The dirt that is there seems to be ingrained enough that it won't shift even with rigorous brushing, but when the fan is running at full speed some of it seems to get released - enough to cause a fine layer of dust on the inside of the machine - and probably in the air it blows out as well.

The machines I've used had dust filters in them, is there not the possibility to put a filter sheet on the inlet side?

There's the standard type of filter that portable air conditioners have. It does not stop fine dust particles like cement. Yes, some cement dust will gather on the part of the filter where the particles happen to build up, but the rest is going straight through the filter.

I am now thinking about removing the entire motor and plastic housing that the fan blades are kept in. I think it is possible - my main concern is the retaining bolt you see in the first photo that goes into the side of the shaft. I wonder if that has to be tightened to some exact torque setting?

 

[Burnerman]

Just tighten that screw enough so that it bites on the motor shaft.....it isn't critical.
I still say compressed air is your best bet - and I mean 100 psi @ 12 cfm. Is there no one who can run you to a garage?
John

 

[foxhole]

It really needs the blade off and dropping in a bucket of brick acid to clean [won't harm plastic blade].
In situ then a small dremel type tool with a mini wire brush may remove.[vacuum away dust] I would not use air as I cannot see it having any effect on dried cement and if it did you might be blowing it into the machine causing more problems.

https://www.dremel.com/en-us/Accessories/Pages/ProductDetail.aspx?pid=516

 

[Bertie78]

Thanks guys. I have made up my mind that I will take it apart when I get the time. I will probably try 99% alcohol as a first resort. When I said I doubted compressed air would work above - I was talking about the spray cans for home use as someone mentioned above. In any case I am concerned a garage might damage the fan blades, and I am not sure these Chinese built units have spare parts easily available.

I will try acid if nothing else works. I have seen it used on Youtube and it's harsh looking stuff - plus I live in a flat with no outdoor space. I'll update the thread when I get it done.

Burnerman, my brother-in-law said the same today, just tighten it without using a torque spanner. I can always run the fan before putting the unit back together to make sure it is doing what it's meant to do. Being a worrier makes for a bad DIY person. You always anticipate the worst - in this case the nut coming loose and the whole unit coming apart. Probably never happen if I tighten it as you said.

 

[Burnerman]

With every respect Bertie I think you are making hard work of this one.....having cleaned literally hundreds of motors out with compressed air it does no harm.....if there is dust inside then its beaten you to it, and if its a sealed motor then there's nothing you can do anyway.
I'd only use solvents if the fan or whatever was contaminated with oil or whatever - there's no real way of knowing where the liquid will go during the process.
As for the fan screw.....nicely finger tight plus 1/4 to 1/3rd turn.
John

 

[JohnD]

I can't see any purpose in using solvents. It isn't grease, it's dust. I have got builders dust off heaps of things by sponging or scrubbing with warm water and WUL. If the material is plastic it will not be adhering very firmly.

 

[Bertie78]

Just an update on this for anyone who needs to clean concrete dust off of plastic. I found warm water and washing up liquid really got rid of it quite easily - I had used old toothbrushes and a "spout cleaner" from Robert Dyas for the harder to reach parts. I had first of all tried white vinegar and although it removed a small amount of the residue it was ineffective overall and a lot of hard work. Thank God I didn't buy or try to use any harsh chemicals.

I don't know how to attach images on this forum now, but the fan unit was clean to the naked eye. A camera flash still brought up a few marks, but there was no longer any dust flying off the unit.

I managed to sell the A/C unit near the end of summer after doing a thorough job, and was glad to see the back of it. I will think twice before buying used electrical items again.