I have a Rainbow D4c. I vacuumed a room no problem, emptied the water and filled it again. Upon turning it back on the arm thing worked, but the main motor of the unit itself did not do anything. It just does not turn on. I flip the switch and nothing, no click, no hum, no smell, just nothing. When I plug the arm into it the arm works just fine. So its just the main unit. I think what might have happened is, for some reason, I decided to put a little bit of a cleaner solution in the water basket. When I stopped after the room was over the water basket was filled with soapy foam, and I think that somehow did something terrible that I'm hoping I can fix without spending a few hundred dollars.

SOURCE: My Rainbow stopped running

I took my unit apart to clean it. I was careful to put it back the same way. Now it won't start.

SOURCE: rainbow vacuum model D4C leaks water,

you can buy them on line, there sticky on 1 side, you need too clean the area after removing the seal.be sure the areas clean so the seal will stick

SOURCE: What's the difference between the rainbow D4C SE

the se has a newer updated version of the power nozzle. the power nozzle is smaller.the d4c is older
than the se. the attachments are pretty much the same and the se is a darker color than the
d4c

SOURCE: can not get the housing off

Remove the 4 screws on the bottom of the canister, and also carefully remove the water basin gasket. You will reattach the gasket with rubber contact cement when you're finished with your repair/cleaning.

SOURCE: motor won't start

Most times this will be caused by one of 3 items, the cord, the switch or the carbon brushes in the motor. Inspect the plug area on the cord for strain twist it gently and look to see if the cord appears a bit white where it meets the plug or if the cord appears crushed just before the plug.
Also inspect where the cord meets the body of the vac for the same signs of wear or any locations where it may have been caught in the power head , etc.
If you have test meter, check for resistance change at the plug while twisting and finally try the same twisting with the vac plugged in if necessary but keep your fingers back from the plug in case the cord blows... gently twist and pull slightly to see if the motor continues to run.
Most often when a switch fails it just dies and doesn't become intermitant... so with a meter it will generally test good or bad , nothing else..
Sometimes on a well worn vac when the motor doesn't start the carbon brushes in the motor have worn down. A heavy duty motor such as the Rexair can often be rebuilt if brushes are required.
If you turn the machine on and bump or jolt the side of the body as if to spin it, you can often "trick " the motor into starting. If this happens it is most likely a carbon brush issue , if not time for a new motor.
Rainbow/Rexair machines have a fairly good motor however because of how they run drawing moist air through they often rust as they age. This is a tedius rebuild and best left to a pro shop with parts on hand if requiring brushes. Most shops will simpley scrap a worn motor if rusty and replace it completely.
Before you spend big $ on a repair or replacement....
One last thing....... pull the exhaust cap at the back of the vac. You will seen fine powder dust and residue.Wipe your finger across it. This is what the Rexair releases into your home each time it runs, but you don't smell it because it comes out in the form of humidity...like after a spring rain.
That same humidity is rusting your motor gradually year by year. Although this motor has a long life span, consider that you have been breathing dirty humidity as it runs. If you put orange drink crystals in the water bucket and run the vac, the exhaust air would smell like orange juice,... so what is in the tank comes out in the air, including your dirty water.
Most Rexair owners buy thinking they are helping to reduce allergins.. yet what is on that exhaust plug proves otherwise. If your home is essentially carpet free and you are vigilant maintaining and rinsing the bucket, you might consider rebuilding this vac.. Otherwise consider a good High end European vac like a SEBO,MIELE, Nilfisk etc for better filtration and reliability