McQuay Mark IV-AC Installation Manual
Operation & Maintenance Data OM 120-2
Mark IV/AC Controller For
Water Source Heat Pump Units
Group: WSHP
Part Number: 578993Y
Date: May 1999
Contents
Features of the Mark IV Controller ................................ 2
Initial Power Up................................................................2
General Use and Information ......................................... 2
Occupied Operation ........................................................ 3
Thermostat Inputs (G, Y1, W1, and W2)........................3
Control Inputs (HP, LT, COF, U, L, E, O) 3
Control Outputs (A and P)..............................................3
Fan Operation................................................................. 3
Cooling Mode ................................................................. 3
Heating Mode.................................................................3
Unoccupied Operation....................................................3
Thermostat Inputs (G, Y1, W1, and W2)........................3
Control Inputs (HP, LT, COF, U, L, E, O) 3
Control Outputs (A and P)..............................................3
Fan Operation................................................................. 4
Cooling Mode ................................................................. 4
Heating Mode.................................................................4
Additional Operating Modes .......................................... 4
Load Shed ......................................................................4
Brownout ........................................................................ 4
©1999 AAF-McQuay Incorporated OM 120-2 (Rev. 5/99)
Remote Shutdown.......................................................... 4
High/Low Pressure Faults..............................................4
Low Temperature Faults ................................................5
Condensate Overflow..................................................... 5
Tenant Override.............................................................. 5
Operation of the Fan during most Modes, Faults &
Shutdowns ..................................................................5
Operation with High Speed Jumper ..............................5
Priority of Faults and Modes..........................................5
LED Status and Fault Output Status .............................6
14-PositionTerminal Strip...............................................6
Trouble Shooting the Mark IV/AC Control Board ........ 6
Interfacing the Mark IV/AC Controller
to External Equipment .................................................7
Typical Mark IV/AC Unit Wiring Diagram...................... 8
Features of the
Mark IV/AC Controller
The Mark IV/AC controller incorporates features which
improve the operation and safety of AAF-McQuay heat
pumps. These features include:
1. Compressor short cycle protection
2. Brownout protection with time delays for the fan and compressor to prevent damage due to low voltage conditions
3. Condensate overflow protection
4. Refrigerant high / low pressure protection
5. Low temperature protection with automatic condenser
defrost cycle
6. Random start delay compressor to prevent high building
electrical demands when multiple units are simultaneously
switched on during power-up, return from brownouts,
return from load shed, etc.
7. LED’s to indicate operational status and fault indication
8. Controlled delay of the reversing valve to reduce annoying “swish” noise
9. High speed test jumper (TP) used to reduce compressor short cycle and reversing valve delay times to
speed system check out and repair.
10. Load shed control input for energy management systems
11. Remote shutdown control input for remote shutdown
of unit
*
12. Unoccupied control input for night setback control
13. Inputs for both standard (W1) and night setback (W2)
thermostats
Initial Power Up
When power is first applied to the unit, the following events
occur:
1. The board executes a reset routine which sets up the
microcontroller for normal operation. During this routine
the following occurs:
a. The reversing valve may click on and off.
b. The A output goes low for a fraction of a second.
c. The GREEN LED will flash at
approximately 1
d. A new random start delay time between 0 and 32
seconds is generated. A new short-cycle timer is
also generated by adding 180 to the new start delay
time for a total time delay between 180 and 212
seconds. Once these numbers are generated, the
same time delays will be used until the next power
cycle.
2. The microcontroller then checks for the following conditions in the following order:
a. High pressure fault
b. Low temperature fault
c. Load shed signal on
d. Brownout or remote shutdown condition
e. Condensate fault
f. Unoccupied signal on
If any of these conditions are true, the microcontroller
executes the appropriate routine. For example, if the high
pressure switch is open upon power up, the compressor
will not start and the RED LED will flash.
3. If none of the above signals or faults are detected during
start up, the unit will go into normal operation.
1
⁄2 seconds.
1
⁄2 second intervals for
14. Fault output for remote fault indication
15. Operation of the fan during most faults and load shed to
increase comfort
16. Tenant override input to manually switch from unoccupied mode (U) to occupied mode (O)
17. Control board inputs U, L, E, Y1, W1, G, W2, and O have
been designed to operate by connecting to the units
24vac, 24vdc, or chassis ground
The remote shutdown input (E) should not be the sole
*
means of ensuring equipment status when used as a part of
a life-safety control system as the unit fan may operate
during some fault conditions.
CAUTION
The Mark IV/AC circuit board incorporates static sensitive
devices. A static charge from touching the device can
damage the electronic components. To prevent damage
during service, AAF-McQuay Incorporated recommends the
use of static discharge wrist straps which are grounded to the
heat pump chassis through a one mega ohm resistor.
For replacement of a Mark IV/AC circuit board:
1. Connect wrist strap to unit.
2. Remove faulty board and place on static protected surface.
3. Remove replacement board from static protected bag.
Do not touch circuit board; hold by edges.
4. Holding board in grounded hand, install board in unit.
5. Insert faulty board in empty static bag for return.
General Use and Information
The Mark IV/AC control board is provided with three drive
terminals, R (24vac), F (24vdc), and C (0vac) 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
or single board drive terminal (R, F, or C) may be used to
operate the Mark IV/AC boards 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 thermostat 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 connected 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 control board’s power terminals.
No solid state devices (Triacs) may be used to operate Mark
IV/AC board inputs. No outside power sources may be used
to operate Mark IV/AC board inputs.
Page 2 / OM 120-2
Occupied Operation
Board LED Status
Yellow Green Red
Off On Off
Thermostat Inputs (G, Y1, W1, and W2)
Thermostat inputs used during occupied operation are G, Y1,
and W1, which when energized will activate the Fan Only,
Cooling Mode, and Heating Mode respectively. Input W2,
unoccupied Heating Mode has no effect during occupied
mode.
The Mark IV/AC board is configured so that when either the Y1
or W1 input is energized the unit fan will also be activated with
Cooling or Heating Modes. In other words, energizing Y1 and G
together will have the same effect as energizing just Y1.
The W1 input has priority over the Y1 input. In situations when
both inputs W1 and Y1 become energized (unlikely) in any order
the unit will go into the Heating Mode as described below:
1. For example, if the unit is in Cooling Mode, Y1 energized, and
W1 becomes energized and remains energized, the following will occur:
l The compressor will be de-energized
l The reversing valve will energize 1 minute later (Heating
Mode position)
l The compressor will restart between 180 and 212
seconds (short-cycle timer)
2. If the unit is in Cooling Mode, Y1 energized, and W1 becomes
energized momentarily the controller will de-energize the
compressor for 180 to 212 seconds (short-cycle timer) and
then return to the cooling mode.
3. However, if the unit is in Heating Mode, W1 energized, and
Y1 becomes energized the unit will remain in Heating Mode.
The board will be in occupied
mode if the unoccupied terminal
(U) is de-energized.
3. The P control output is de-energized when the compressor
is energized
When the Y1 terminal is then de-energized, the following
will occur:
1. The compressor is de-energized immediately
2. The fan is de-energized immediately, unless the G terminal
is energized
3. The P control output is energized when the compressor is
de-energized
Compressor time delays may be longer than indicated above as
the short-cycle timer (180 to 212 seconds) will be used as
needed to prevent adverse compressor cycling.
Heating Mode
The W1 terminal controls occupied Heating Mode operation.
When the W1 terminal is energized the following will occur:
1. The reversing valve will be energized immediately
2. The fan will be energized immediately
3. The compressor will be energized after 0 to 32 seconds (start
delay timer)
4. The P control output is de-energized when the compressor
is energized
When the W1 terminal is then de-energized the following will
occur:
1. The compressor will be de-energized immediately
2. The fan will be de-energized immediately, unless the G
terminal is energized
3. The reversing valve de-energizes after 1-minute
4. The P control output is energized when the compressor is
de-energized
Compressor time delays may be longer than indicated above as
the short-cycle timer (180 to 212 seconds) will be used as
needed to prevent adverse compressor cycling.
Control Inputs (HP, LT, COF, U, L, E, O)
The control inputs are High / Low Pressure (HP), Low Temperature (LT), Condensate Overflow (COF), Unoccupied (U), Load
Shed (L), and Remote Shutdown (E). The control inputs will all
be in their normal states during occupied mode. The state of
each control in occupied mode during normal operation is as
follows:
l High / Low Pressure (HP): energized, switch is closed (no
fault)
l Low Temperature (LT): energized, switch is closed (no fault)
l Condensate Overflow (COF): sensing no condensate water
(no fault)
l Unoccupied (U): de-energized (no signal)
l Load Shed (L): de-energized (no signal)
l Remote Shutdown (E): de-energized (no signal)
l Tenant Override (O): has no effect in occupied mode
Control Outputs (A and P)
The control outputs are Alarm Fault (A) and Pump Request (P).
The operation of the control outputs during occupied mode is
as follows:
l Alarm Fault (A): energized (no fault)
l Pump Request (P): energized when the compressor is off,
and de-energized when the compressor is on.
Fan Operation
The G terminal controls Fan Only operation. The fan will start
when the G terminal is energized. De-energizing the G terminal
will cause the fan to stop unless the W1 or Y1 terminals are
energized.
Unoccupied Operation
Board LED Status
Yellow Green Red
On On Off
Thermostat Inputs (G, Y1, W1, and W2)
The only thermostat input used during unoccupied operation is
W2, which when energized will activate Heating Mode. Inputs
G, Y1, and W1 have no effect during unoccupied mode.
Control Inputs (HP, LT, COF, U, L, E, O)
The control inputs are High / Low Pressure (HP), Low Temperature (LT), Condensate Overflow (COF), Unoccupied (U), Load
Shed (L), and Remote Shutdown (E). The state of each control
input during unoccupied mode during normal operation is as
follows:
l High / Low Pressure (HP): energized, switch is closed (no fault)
l Low Temperature (LT): energized, switch is closed (no fault)
l Condensate Overflow (COF): sensing no condensate water
(no fault)
l Unoccupied (U): energized (signal provided)
l Load Shed (L): de-energized (no signal)
l Remote Shutdown (E): de-energized (no signal)
l Tenant Override (O): see section “Tenant Override Mode”
The board will be in unoccupied
mode if the unoccupied terminal
(U) is energized.
Cooling Mode
The Y1 terminal controls Cooling Mode operation. When the Y1
terminal is energized, the following will occur:
1. The fan will be energized immediately
2. The compressor will be energized after 0 to 32 seconds (start
delay timer)
Control Outputs (A and P)
The control outputs provided by the Mark IV/AC board are
Alarm Fault (A) and Pump Request (P). The operation of the
control outputs during unoccupied mode is the same as in
occupied mode. See occupied operation.
OM 120-2 / Page 3
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