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71
YORK INTERNATIONAL
FORM 100.50-NOM1 (604)
5
FIG. 38 –
LOW AMBIENT HARDWARE
FIG. 39 –
CONDENSING PRESSURE CONTROL PROPORTIONAL BAND
To summarize the control, the MOD UNT monitors
the condensing pres sure at an ap pro pri ate input. The
Primary Unit Controller will read the con dens ing
pres sure, perform the con trol logic, and command the
MOD-UNT to in crease or decrease the output to the
VFD, as required. The fol low ing
Þ
gure il lus trates the
control logic re quired for this control loop.
LD06574
100%
Output
to VSD
0%
-15 psi
Discharge Pressure
Control Setpoint
+15 psi
Condensing Pressure
LD06575
Condenser Fan
MOD-DCU
N2
MOD-
UNT
Condensing Pressure
Transducer
VSD
3Ø POWER IN