York YS Slide valve control

[sr71blackbrd]

We have a 250 Ton York YS that just started driving the slide valve full open and not unloading when the water reaches setpoint. The control side appears to be working correctly but the valve is not.
I have watched it operate in the service mode where you can see the pulse for load and unload signals. With gages attached to both sides of the actuator you can see the pressure go up on the unload side but the valve does not move. If you go to manual and give it a constant unload signal it will drive the valve closed. Same pressure rise.
The Technician has already changed out the solenoid valve part that is attached to the top of the 4 Way directional valve sub plate.
Has anyone had this problem?

[servicetrane]

you email?

[sr71blackbrd]

Yes.

You wouldn't happen to know if there are service bullitins for York equipment?
What about shop drawings showing the slide valve assembly?

Thank you
Joe

Joe,

No e-mail addresses allowed in posts. You may put it in your profile.

Thanks,

Mod Team

[servicetrane]

check you mail

[mschaver]

The slide valve is operated via oil pressure. The slide valve is stuck. There should be a 1/4" access port on the end of the slide valve piston. Remove and force slide valve to move. This is the process for a Trane screw. Im not entirely sure for a york, but its very similiar. There should be a service bulletin. Hope it helps

[klove]

Before you start in the wrong direction, your SV is not stuck. If it were, it wouldn't load and unload when in service mode with a constant signal. From your explanation, it sounds like the slide valve piston seals may be bypassing oil from one side of the cylinder to the other. The key is that the SV loads/unloads and the controls work, but the pulse width of the load/unload signals won't keep up with what the valve wants to do on it's own during normal operation.

[Bklyntek]

One of our techs,diagnosed this problem yesterday. Turns out
That the intern seals are damaged. Works fine in manual mode,
But wouldn't unload in remote mode. Will have to pull
Compressor and replace. Not sure personally, if it could be field
Repair. He has 22 years in business with York, I trust his
Judgement.

[sr71blackbrd]

I'm sorry folks. I should not have left you hanging. It was a simple fix that will probably be required every 30,000 hours.

The two things that were found bad was the slide valve pot control shaft. The helical groove was worn.

The slide valve actuator piston rings were worn approximately .025" thinner than the new ones.

They also replaced the hydraulic control solenoid valve for the actuator but that didn't solve the problem. This was the first thing they tried.

The actuator cylinder did not appear to be worn at all. Nor did the piston shaft and slide valve return spring.

The slide valve has been controlling correctly since it was put back into service in May, 2011.

This is a field repair.