How can I fit the spring in my pressure switch control unit- Model 520M?

You need to seat it with the plastic catch holding it in place, so that it can not possibly short out to the electrical lugs. 2nd, you will not be able to reinstall the switch cover unless the V clip is compressed! Get a short piece of nylon twine, and run it around the Vclip (where it touches the microswitch) and run the two pieces of twine outside of the plastic switch housing. Pull on the 2 pieces of twine to compress the V clip as you install the switch top cover. After you have one of the screws in, pull on one end of the twine to remove it!
Remember to bleed the water through the karcher in order for the water pressure switch to activate and the motor to start.

William J
September 2012