Setpoint - McQuay MicroTech Unit Controller Installation And Maintenance Data

OPERATING SEQUENCE
The following describes the unit's normal operating sequence
provided the time delay requirements are met and no safety
control has tripped or holiday schedule set to keep the unit off.
Place the control panel "Stop-Auto" switch in the "Auto"
position.
In this position the switch is engaged and the unit may be
started provided:
1. The chilled water sensor is calling for cooling.
2. No time delay is restraining operation.
3. A remote start-stop switch (See SW2 in the control wiring),
is not open preventing unit operation.
4. No safety switch has been tripped and not reset.
Press the "Start Unit" key switch. The following messages
appear in the display screen, in sequence, indicating action
which has taken place.
FUNCTION
Will start in XX minutes*
Evaporator pump
W a i t i n g f o r
O i l p u m p i s o n
C o n d e n s e r p u m p i s o n ( A d j u s t a b l e ) .
M C R i s
Unit is running okay
* Programmed safety time delayed start is based on a factory set 40 minute
start-to-start but not less than 3 minutes between stop-to-start.
The statement displayed "Waiting for load" in the above se-
quence, and the countdown period in seconds assigned to
it, assumes that the water temperature sensed by the chilled
water temperature sensor may not represent the entire chill-
ed water system temperature if the chilled water pump has
been shut off. This delay interval provides time for the chill-
ed water pump to circulate system water and impart a valid
system water temperature to the chilled water sensor.
In the starting sequence:
1. A call for cooling will energize the control through the logic
output circuit to the evaporator water pump relay coil.
If the circuit to this solid-state relay is completed the LED
at the solid-state relay supplying that control power will
glow.
2. If the evaporator water pump relay's operation results in
operation of the chilled water pump, then closure of proof
of flow contacts and interlocks will permit the next step.
Proof of flow will also light LED number 9 on the daughter
board.
3. An oil temperature sensor (#10) must indicate an oil
temperature at least 40°F above the saturated refrigerant
evaporator temperature (#2 sensor).
4. If steps 2 and 3 are satisfied, the oil pump contactor is
energized through the logic output circuit. The oil pump
motor is started.
Simultaneously with the starting of the oil pump motor,
the 115 volt circuit supplying power to the oil pump heaters
is opened de-energizing them.
5. With the oil pump operating, a minimum oil pressure of
60 PSIG above evaporator pressure is required to com-
plete the sequence for the next step.
6. Following proof of adequate oil pressure and the passage
of a 60 second prelube time, the condenser water pump
relay is energized, through the logic output circuit. Again
proof of the logic instruction to this circuit is evidenced by
the glow of this solid-state relay's LED. If the CWR relay
is energized and this action results in closure of the flow
switch and interlock between terminals 10 and 61, LED
number 8 on the daughter board will glow, confirming com-
Page
22 / IM 403
COUNTDOWN TIME
on. 2 0
l o a d . . ( V a r i a b l e ) ( s e c o n d s )
3 0 or 60 (seconds)
( V a r i a b l e ) .
05 (seconds)
o n .:'I X X ( s e c o n d s )
OPERATION
pletion of this starting step.
7. Within 5 seconds of energizing the condenser water pump,
if the compressors' vane closed switch shows the vanes
to be in a closed (compressor unloaded) position, the logic
output circuit (14) is completed through closed mechanical
contacts to control panel terminal 5A, back through the
solid-state latch-in circuit, and through to the main starter
operating coils, (MCR1, and MCR2).
The latch-in circuit is a normally open contact solid-state
relay. Upon the application of a logic signal, the relay
closes its contacts instantly. They remain closed for 3
seconds, then open. The operating contacts are in parallel
with normally open MCR coil contacts. These close and
serve to prove the operation of the compressor motor
starter coils. Closure of interlocks, and the transition relay
also serve to confirm normal and complete starter
operation.
8. Throughout this entire process, conventional protective
controls remain active to interrupt the starting sequence
in the event of a fault.
(seconds)
9. An incomplete sequence is recorded as a fault and trip.
If the fault occurs because of the failure of the logic out-
put circuit to complete a
LED may be lit, but the LED on the daughter board for that
circuit will not be lit. NOTE: a blown fuse in the solid-state
relay circuit (see Figure 29), or an open in the operating
circuit beyond the solid-state relay will not prevent the solid-
state relay's LED from being lighted. See section on Trou-
ble Analysis.
TEMPERATURE CONTROL OPERATION
Temperature sensors are negative co-efficient thermistors
selected for extended accuracy and close control. During com-
pressor operation from 10% to 100% capacity chilled water
operating temperature will be held to within +05"F.
The operator shall input the design leaving chilled water
temperature by first pressing the water temperature keypad
under the "Setpoints" section of the control panel.
The setpoint value listed in the program will then be
displayed in the window above the keypad.
If the value displayed is the desired temperature, no fur-
ther action is required. The "Cancel, Clear Display" keypad
should be pressed to clear the screen.
If the value displayed is not the desired setpoint
temperature, the value may be changed by:
1. Press the "+/Yes" or "-/No" keypad. The display will read
"Enter Password" if a password has not already been
entered. NOTE: All setpoint and service changes require
use of a password.
2.
Enter the required password. The operator password may
be' entered by pressing the "?/HELP" keypad four (4) times
in succession.
3. The display will then read, "Operator Password Okay".
4. Re-press the water temperature setpoints keypad to display
the leaving chilled water temperature. To raise the value
displayed, press the "+/Yes" keypad. To lower the value
displayed, press the "-/No" keypad.
5.
When the revised, desired, setpoint is displayed, it must
be entered into the program by pressing the "=/Enter"
keypad.
Other Operator controlled setpoints are changed in the same
manner. The cycling "on-off" thermostat function is programm-
ed into the MicroTech software. An operating unit will shut off
when the leaving chilled water temperature is pulled down,
(at 10% compressor capacity) to 2°F below the leaving chill-
sequence,
the solid-state relay's