Bard MC4000 Low Voltage Field Wiring, Controller Grounding, Controller Power-Up, Blower Operation

LOW VOLTAGE FIELD WIRING

The MC4000 is powered from the air conditioners that it is controlling, 24 VAC (18-32V) low voltage only.

Circuitry in the MC4000 isolates the power supplies of the two air conditioners so that no back feeds or phasing problems can occur. Additionally, if one air conditioner loses power, the MC4000 and the other air conditioner are unaffected and will continue to operate normally.

Connect the low voltage field wiring from each unit per the low voltage field wiring diagrams in Section on “Controller Wiring”. NOTE: Maximum of 18-gauge control wiring should be used. Using heavier gauge wiring can create excessive stress on the control board as door is opened and closed. Create a wiring loop so the door can open and close without stressing terminal blocks.

CONTROLLER GROUNDING

A reliable earth ground must be connected in addition to any grounding from conduit. Grounding lugs are supplied for this purpose.

CONTROLLER POWER-UP

Whenever power is first applied to the controller, there is a twenty (20) second time-delay prior to any function (other than display) becoming active. This time-delay is in effect if the controller On/Off button is used when 24VAC from air conditioners is present, and also if controller is in “ON” position and 24VAC from air conditioners is removed and then restored.

FIRE SUPPRESSION CIRCUIT

To disable the MC4000 and shut down both air conditioners, terminals F1 and F2 may be used. The F1 and F2 terminals must be jumpered together for normal operation. A normally closed (nc) set of dry contacts may be connected across the terminals and the factory jumper removed for use with a field-installed fire suppression system. The contacts must open if a fire is detected. See appropriate connection diagram - Figures 1, 2 or 3 for this connection. Contacts should be rated for pilot duty operation at 2 amp 24VAC minimum. Shielded wire (22-gauge minimum) must be used, and the shield must be grounded to the controller enclosure.

IMPORTANT NOTE: Older Bard R-22 models employ an electronic blower control that has a 60-second blower off-delay. Current production R-410A models do not use a blower off-delay device and the remainder of this (paragraph) does not apply. In order to have immediate shutdown of the blower motor, in addition to disabling the run function of the air conditioners will require a simple wiring modification at the blower control located in the electrical control panel of the air conditioners being controlled by the lead/lag controller. To eliminate the 60-second blower off-delay, disconnect and isolate the wire that is factory-connected to the “R” terminal on the electronic blower control, and then connect a jumper from the “G” terminal on the blower

control to the “R” terminal on the blower control. The electronic blower control will now function as an on-off relay with no off-delay, and the blower motor will stop running immediately when the F1-F2 fire suppression circuit is activated (opened).

STAGING DELAY PERIODS

The following delays are built in for both cooling & heating:

Stage 1 – 0 seconds for blower (if not already on as continuous)

10 seconds for cooling or heating output

Stage 2 – 10 seconds after Stage 1 for blower

10 additional seconds for cooling or heating output

Stage 3 – 10 seconds after Stage 2

Stage 4 – 10 seconds after Stage 3

Note: For cooling Stages 1 and 2, the stage LED will blink for 10 seconds while the cooling output is delayed after that stage is called for. There is also a delay after the stage is satisfied, and after the LED stops blinking, the stage will turn off. There is a minimum 10-second delay between stages 2 & 3, and 3 & 4, but no delayed output when stage is turned on or off, and LED for those stages will not blink.

BLOWER OPERATION

The controller can be configured to have main HVAC blowers cycle on and off on demand; have all blowers run continuously; or have the lead unit blower run continuously with the lag unit blower cycling on demand. Default setting is the blower(s) start and stop on demand. There is also an option to have all blowers cycle on if one remote sensor is connected, and a temperature difference of more than 5F between any two sensors is observed. This helps to redistribute the heat load within the structure and should reduce compressor operating time.

When any of the stages are satisfied, the stage LED will blink for ten (10) seconds before the stage is actually turned off.

ADVANCE (SWAP) LEAD/LAG UNIT FEATURE

Pressing the Advance button for one (1) second will cause the lead and lag units to change positions. This may be useful during service and maintenance procedures.

ACCELERATE TIMER FEATURE

Pressing the UP arrow button for five (5) seconds will activate an accelerate (speed-up) mode, causing the normal changeover time increments of days to be reduced to seconds. Example: 7 days becomes 7 seconds. When “ACC” displays, release button. Whichever LED is on, indicating lead unit will blink over for each second until the controller switches. This is a check for the timer functionality.

Manual	2100-563C
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