IM 778 / Page 23
14-Position Terminal Strip
Pin Designation Description
1CTransformer ground (Ovac)
2RTransformer supply (24vac)
3V-DC power connection
4PPump request output
5AAlarm fault output
6UUnoccupied input
7LLoad shed input
8ERemote shutdown input
9F+DC power connection
10 Y1 Occupied cooling mode input
11 W1 Occupied heating mode input
12 G Fan only input
13 W2 Unoccupied heating mode input
14 O` Tenant override input
Board Status LED’s Fault Output
Mode Yellow Green Red Terminal A
Occupied Off On Off Energized
Unoccupied On On Of Energized
Load Shed Off Off On Energized
Condensate Overflow On Dim Off De-Energized
High/Low Pressure Fault Off Off Flash De-Energized
Low Temperature Fault* Flash Off Off De-Energized
Brownout Off Flash Off De-Energized
Emergency Shutdown Off Flash Off De-Energized
*in heating mode only
Note: The fault output is energized when no faults exist. The fault ouput is
de-energized during faults and when unit power is off.
The Mark IV/AC control board is provided with three drive terminals, R(24vac),
F(24vdc), and C(Ovac) that can be used by the end user to drive the thermostat
inputs (G, Y1, W1, and W2) and control inputs (U, L, E, and O). Any combination of
a single board drive terminal (R, F, or C) may be used to operate the Mark IV/AC
board’s control or thermostat inputs. However, only one drive terminal (R, F, or C)
can be connected to any individual input terminal or damage will occur. Some of the
control inputs are used within the Water Source Heat Pump and not accessible to
the end user. For example, HP, LT, and COF are not available for use by the end user.
Typically the Mark IV/AC board’s R(24vac) terminal is used to drive the board’s ther-
mostat inputs and control inputs by connecting it to the R terminal of an industry
standard thermostat. The control outputs of the standard thermostat are then con-
nected to the Mark IV/AC board thermostat inputs and control inputs as needed.
Any remaining board input(s) may be operated by additional thermostat outputs or
remote relays (dry contacts only).
All Mark IV/AC board inputs must be operated by dry contacts powered by the con-
trol board’s power terminals. No solid state devices (Triacs) may be used to operate
Mark IV/AC board inputs. No outside power source may be used to operate Mark
IV/AC board inputs.
Using Drive Using Drive Using Drive
Terminal R (24vac) Terminal F (24vdc) Terminal C (ground)
De-engergized Energized D-energized Energized De-energized Energized
Place the Meters
Red (+) Lead on
Place the Meters Place the Meters Place the Meters
Input to be
on Black (-) Lead Black (-) Lead Black (-) Lead
checked
on C on V on R
U, L, E, Y1, W1, 10 to 22 to
Ovdc
30 to 10 to 22 to
G. W2. P 14vac 26vac 33vdc 14vac 26vac
LED Status and Fault Output Status
General Use and Information
Mark IV/AC Sequence of Operation
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