York YS Chiller

[curlydogmaster]

One of my York YS chillers is not controlling its slide valve well and is cycling too much. Today I observed it running at 42.4 with a set point of 46. It was still at 93% slide valve and "current limit in effect" (95% of full load). I stepped in and manually unloaded it and it responded correctly. Also, when it first starts and is running in demand limit it is able to accuratly control its slide valve.
I don't see why it wants to "drive itself over the edge" like that. Any thoughts?

[york56]

Have you looked at the potentiometer they always seem to have problems dead spots on the the wiper just a thought.

[curlydogmaster]

It smothly and accuratly loads and unloads when operating in "demand limit", "current limit", and "manual" modes. It's only when funning in "full auto" mode that it runs wide open until cycling off on low limit. I'm thinkin it has a PROM issue...???
Last summer it had an issue with the starter and the trigger board had to be replaced. Could it be that whatever took out the trigger board also damaged the "mother" board as well?

[york56]

When you say that you run it in "full auto" is that in "local' or "remote" mode anything is possible in regards to what happen to the starter if the e-prom is corrupt I would think no matter what you tryed it would have problems , but there could be a problem with the microboard and chip.

[curlydogmaster]

By "full auto" I mean that it is in "auto" and the "demand limit" has timed out so it is free to load and control to chilled water setpoint.

It is in local mode but I'll double check it. I know what you are saying and that's how it acts: like it's waiting for a remote setpoint reset.

[york56]

All machines have current limit on start up they have a time that they hold back the machine or they are allowed to take right off and go you can change that if you want let me know if you need help. single line panel or optiview.

[curlydogmaster]

Yes, that's exactly what I've done to over come the problem for now.

I set the "pull down demand" (demand limit) to 65% for 20 minutes and then knocked the current limit down to 85% and that "keeps her at a trot" so to speak but it's not right...

[servicetrane]

hello mr york
service bulletins looking YORK machine model YS

[referteacher]

Chilled water thermistor gone bad???? I've hd YT's where that has happened. If they're not sealed well in the thermo-well, condensation can throw the calibration off.

[curlydogmaster]

When you say that you run it in "full auto" is that in "local' or "remote" mode anything is possible in regards to what happen to the starter if the e-prom is corrupt I would think no matter what you tryed it would have problems , but there could be a problem with the microboard and chip.

MYSTERY SOLVED:

Your coment about "local" or "remote" got me thinkin'.
This machine does have a #2 Option Board installed so that the energy (mis)management system can adjust the setpoint. A quick snip-snip and she's under her own control now...

Thanks for gettin' my wheels turning!

[york56]

Glad to here that you resolved the problem good job.