York YD A, Operating & Maintenance, Page: 18 / 52

JOHNSON CONTROLS
18
FORM 160.69-O2
ISSUE DATE: 9/30/2020
SECTION 1 – DESCRIPTION OF SYSTEM AND FUNDAMENTALS OF OPERATION
FIGURE 2 – CHILLER OPERATION FLOW CHART - (CONT'D)
LD10490
2 Compressors Running
(from Page 3)
Electro Mechanical Chiller
Capacity Cycling (Lag Compressor Stop) Sequence
Has Lag
Compressor
Run >30 Min
No
Yes
Motor Current
<XXX for
Time T
Decision to Stop
Lag Compressor
Close Lag Compressor
Discharge Valve
Lag Compr Disch
Valve Closed?
Stop Lag Compressor
Motor
Drive Lag Compressor
vanes closed
Post Lube Run Time
Lag Compressor
Yes
No
Yes
1 Compr Running
(Restart 2nd compr if
needed per previous)
As motor currents fall below 50% with
two compressors running, a single
compressor should be able to handle the
load. Field adjust % current range from
30 to 70% of FLA with default of 50%.
> 40 Seconds
Soft shutdown
Wait for Lead compressor
and both PRV closure
No
PRV Motor Switch Closed
or 150 Seconds
Disable VGD Position
Override Function
YD Dual Compressor Chiller