146
YORK INTERNATIONAL
FORM 201.19-NM8 (804)
Micro Panel Contents
1.22 3 OR 4 COMPRESSOR CHILLER
CONFIGURATION
The EPROMs are identical in 3 and 4 compressor units. To
place the software in 3 compressor mode, a jumper must
be connected between J4-3 and +24V on the microboard.
This connection can be made between terminals 13 and
75 on the terminal block. If the jumper is not installed,
the unit will operate as a 4 compressor unit.
1.23 ECONOMIZER SOLENOID CONTROL
The economizer solenoid is controlled by the micro
based on the ability of the economizer to provide extra
capacity according to system operating conditions. This
ability is primarily based on outside ambient tempera-
ture. If the ambient is low with associated low discharge
pressure, the economizer will provide very little extra
subcooling. At an ambient of 90ºF (32ºC) or above with
associated high discharge pressure, the economizer will
begin to provide appreciable additional subcooling. The
extra subcooling may be as much as an additional 20ºF
to 25ºF (-7ºC to -4ºC), often making the total subcooling
at the TXV over 40ºF (4.4ºC).
This should not be confused with
subcooling at the liquid valve, which
should generally be 12ºF to 15ºF (6.7ºC
to 8.3ºC). The micro monitors the dif-
ference in pressure ratio between the
discharge and suction pressure along
with the step of unloading to determine
economizer solenoid on/off points.
The micro utilizes the formula below to compute pres-
sure ratio:
PR = (DP in PSIG)+14.7
(SP in PSIG)+14.7
For the fi rst 3 minutes of operation, the micro will not
energize the solenoid. After 3 minutes of operation. If
the step of unloading is above step 47 and the PR>2.2,
the micro energizes the economizer solenoid.
Once on, the solenoid will remain on until the PR<2.0
or the step of unloading falls below 44. If the condi-
tions drop below either of these points, the micro will
turn off the solenoid.
Economizer cycling is reduced by 2 timers. The timer
with the longest remaining time will dictate when the
economizer can turn on. The fi rst timer is an "on to on"
timer which assures at least 10 minutes elapses from the
time the economizer turns on, off, and then on again a
second time. The second timer assures that a minimum
of 3 minutes elapses from the time the economizer turns
off to the next time it is called to turn on again.
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