My Polaris 3900 Sport was left by the previous homeowner. No idea how old it is, but it's definitely the older style, before Polaris fixed various design issues. It was kept in the pool all the time, and ran on a timer for a couple hours everyday.
First off, it cleans. The wheels turn and the bag fills with leaves and sand. The bag has a 3" rip, but a new one is on its way. I've cleared the in-line filter.
My issues with it are:
1) It doesn't back-up. My pool has cake-like steps and the cleaner gets stuck all the time. The back-up valve cycles on/off at the expected intervals, but doesn't seem to have enough pressure to actually move the unit backwards. There's always a steady trickle from the valve and what seems to be a healthy gush during the back-up cycle. I was able to open the collar fairly easily, found no cracks on the case, and the gears turn and operate the valve as expected. A post in another thread indicated there should be ZERO flow from the back-up valve during the forward thrust cycle. Would replacing the o-rings be the right move ($5), or better to replace all the internals ($40)? Considering tossing the whole valve also ($50).
2) The sweep hose doesn't move at all. I've turned the adjustment knob all the way in both directions. The hose sprays water, but just doesn't whip around. Not even a little. There's no scrubber on the tail, but I've got one in the mail. Just realized that I should've just ordered a TailSweep Pro had I done a little more reading.
3) The black inside plastic part of the pressure relief valve seems worn. Not sure if this could be affecting the above issues, but wondering if i need to replace it.
Has anyone upgraded their 3900 with the new/improved tune-up kit? Seems like it addresses drive related issues rather than any sweep or back-up functions, but just curious.
Here's video of my back-up valve in operation.