Honeywell W7900 won`t shut off

[h2045]

We have a W7900 in a Trane air cooled recip chiller with 2 Model R compressors set up for 6 stages of cooling. The 6 stages are set on a dial on face of the controller itself, not a resister like the W7100 uses. We are running a 30% propylene glycol solution. Problem is as setpoint is approached and passed the last stage of cooling does not shutdown and the temp just keeps dropping. Our mechanic replaced the controller with a used one we had laying around and it does the same thing, the LCW sensor was ohmed out and tests good. Any ideas? Sorry about not having the chiller model #. Thanks for any input.

[nyrb]

I can't even find a w7900 on Honeywell's website, it's likely OEM to Trane the only info I can find is at the link.

http://members.cox.net/epittman2/hvac-talk/CGWC-SB-2A.pdf

[h2045]

Looks like you`re right and Thanks

[DaveCR]

...Our mechanic replaced the controller with a used one we had laying around and it does the same thing...

Can we guess why the used one was lying about?

The problem you are seeing is probably an internal issue to the W7900. We've been replacing, retrofitting actually, these regularly over the past couple of years.

[h2045]

The problem you are seeing is probably an internal issue to the W7900. We've been replacing, retrofitting actually, these regularly over the past couple of years.

What are you using as a retrofit?

[DaveCR]

Johnson FX07.

[Robert1078]

H2045
So you have and obsolete Honeywell 7900. I have had to up-grade five of them in the last three years. I have used the MSC Magnum. The controller is a chiller control so you get all of the fuzzy logic needed to try to keep the chiller running. It has worked out as an excellent recontrol of the chiller and made for a happy owner. My e-mail address is in my profile if you would like more info.
Robert1078

[Tranetek]

You can use a Trane TOL101 to check out a w7900. Comes with all connections and instructions for checking it out