York chiller cycling on suction pressure.

I have a 30 Ton chiller YCAL0030SC17 Millium control. I've replacer the touch pad, a compressor, and contactor. When I got to this machine it had
"Tattle-tales" all over it. (Should have been my first clue) The unit runs great with one compressor disconnected. Now that it's getting cooler, I set the setpoint higher than the actual water temperature and it continues to run. Doesn't drop a compressor of or add hot gas. I hate to just change parts, but I'm thinking it's the control board. any sugestions?

You checked the equivalence of the water temperature sensor (ohms), is that correct?

Welcome to the forum Mike.

As was once explained to me, and from memory so allow me some inaccuracies here!
Basically the software controlling around the set point is really quite sophisticated. The set point is actually the midpoint of the control range.
IE 6.0c +/- 1.5c. I believe this range can be altered. Anyway the operating range would actually be 4.5c to 7.5c in my example. Add to this the fact that there are coincidence timers, where a response in either direction is delayed by 60 seconds.
Therefore your control responses are slow and even with potentially quite a slow response time.Further to this the control system / software responds according to how ever many comps it sees available.

(Add into it alternate loading -irrespective of availability) on recips--- realised Whilst driving down the motorway after my original post AM, this was not so relevant to a YCAL as I believe they may rely on each com stage.
Not so sure on that aspect.
So if you have some comps turned off, chiller response will be even slower, or just sit there?
Or something similar to that!

You are looking for a problem that may well not exist?
Simple answer is if it is faulting the event will be in the history, if it is in a dead zone you should see no change in the load or unload conditions.
With maybe just the discharge pressure rising and falling as the condenser fans operate on and off.
If the system does indeed want to load up the other comp No2? and cannot you will also get to a stage where the system is in limbo? I would assume, but don't quote me on that!
Grizzly