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Manual 2100-574
Page 13 of 23
CONTROLLER WIRING
The MD4000 can be used for controlling two (2) air
conditioners with economizers.
SECURITY (LOCKING) FEATURE
The MD4000 controller can be locked such that
unauthorized persons cannot make any changes
to temperature set points or any other selectable
parameters of the controller system.
The ON/OFF and Comfort buttons remain fully
active for their normal intent. The Advance/Change/
Save button remains active for the Advance feature
only, which allows the position of the lead and lag air
conditioners to be swapped (reversed). The Program
button remains partially active - allowing the review
of temperature sensor(s) actual reading of temperature,
and the current settings/choices that have been chosen.
However, no changes can be made when the controller
is locked, and if the change button is pressed when in
the Program mode, the display will come up showing
“Locd” instead of ashing the selectable choices for
that parameter. The default (DEF) reset capability is
also disabled when the controller is in locked mode.
Locking and Unlocking the MD4000 Controller:
1. Locking the controller requires using 3 buttons
while the controller is in the normal operating (run)
mode.
2. Press and hold the Advance/Change/Save button
and the Up and Down arrow buttons simultaneously
for 20 seconds until the display shows “Locd”.
3. To unlock the controller, press the Change, Up and
Down arrow buttons simultaneously for 20 seconds
until the display reads “uLoc”.
GENERATOR RUN / ECONOMIZER
SHUTDOWN FEATURE
If desired, the MD4000 controller can be signaled
from a standby generator system to lockout (disable
operation of the) lag air conditioning system and close
economizers if active. This is sometimes mandated if
the generator size is not sufcient to handle the building
load (amperage) and that of both air conditioning
systems.
A normally closed (NC) dry contact as part of generator
controls is required. These contacts must open when
the generator is started, and such action will signal the
MD4000 controller to this condition and disable lag
air conditioner run function and close economizers if
active.
A wire jumper is factory-installed across the Generator
Run / Economizer Shutdown terminals. To utilize
the generator run feature, remove the jumper from
Generator Run / Economizer Shutdown, and connect
the generator normally closed (NC) contacts that will
open-on-run generator condition to the Generator Run /
Economizer Shutdown terminals.
BACKUP DC POWER CONNECTION
There are input connections available for -24VDC or
-48VDC (-20 to -56V) backup power connection. Making
this connection will maintain microprocessor operation,
front panel display, LED signaling, and alarm relay
operation during periods of commercial power outages
and when no standby generator is available. This circuit
is protected by a replaceable .5A (500mA) 250V fuse.
IMPORTANT: The shelter DC battery power must
be connected to the controller and wired as shown in
controller wiring diagrams.
The backup DC power connection is polarity
sensitive. If polarity is reversed, the controller will
not function on backup power, no display and no
alarm functions will be evident.