York YD A, Operating & Maintenance, Page: 17 / 52

JOHNSON CONTROLS
17
SECTION 1 – DESCRIPTION OF SYSTEM AND FUNDAMENTALS OF OPERATION
FORM 160.69-O2
ISSUE DATE: 9/30/2020
1
FIGURE 2 – CHILLER OPERATION FLOW CHART - (CONT'D)
LD10489
Start Lag Compressor
Motor
Open Lag Compressor
Discharge Valve
Is Lag Compr
Disch Valve
Open?
PRVs and
Disch Valve on
Lag Compr
should still be
closed
Yes
Reselect Lead Compr
Based upon Run Time
Set High Head Override = False
(Allow Lead Compressor
PRVs to control per LChWT control)
Lag Compr PRVs are
controlled to follow %
motor current of Lead
System Run
Two Compressors
>40 Seconds
Alarm/Fault
No
Delay 50 seconds
To allow motor starting
transition time
Are Motor Currents
Equal within 5%
Yes
2 Minutes after valve
open
End VO valve
transition period.
Level set points
returned to normal
Yes
Normal Safety Checks
(Except for oil low temp
differential)
Lag Vanes
<
Lead Vanes
Yes
No
Does Surge
Exist
No
No
Refer to Anti-Surge
Control Algorithm
Yes
Electro-Mechanical Starter
Chiller Start Sequence
Lag Compr
Startup
From
Page 2
Enable VGD position
override function
Lag Vanes >
80% of Lead
Vanes?
Yes
No
YD Dual Compressor Chiller