Operating instructions

14
pumps from receiving high voltage through the common
wiring if it is turned off at the circuit breaker for service.
Power is supplied to the thermostat by connecting the R
and X terminals to the heat pump terminal strip. The Y
terminal energizes the compressor. The unit is put into
the cooling mode when the thermostat energizes the O
terminal, which operates the 4-way reversing valve. The
L terminal is used to power the lockout LED on a
thermostat, which indicates a compressor lockout. The
pump relay is connected to the circulation pump's 3 pole,
high voltage terminal block (BP). The hydronic side
circulation pump receives power from BP, which is
energized by the pump relay.
A simple, single stage heating aquastat on a storage tank
or wall mounted thermostat may be all that is required for
simple heat only systems. This aquastat closes and passes
power to the Y terminal, energizing the compressor and
circulation pumps in the heating mode. When mounting
an aquastat inside a storage tank, always use a
submersible type aquastat. The aquastat should be
installed approximately 1/3 of the way down into the tank.
Set the aquastat differential to 15
o
F to avoid short cycling
A cooling aquastat can be mounted on the water supply
line, as shown in Figure 4. This aquastat acts as a low
limit, which shuts the heat pump down when the cooling
water reaches a minimum (e.g. 35
o
F).
Changeover from heating to cooling can be achieved in
two ways:
1) A manual toggle switch to select the control
aquastat (heating or cooling)
2) A cooling thermostat which powers the coil of a
single pole/double throw relay which selects the
heating aquastat (normally closed contact) or
cooling aquastat (normally open contact) shown
in Figure 4.
)Note: Always wire the system to shut down (Anti-
short-cycle) between a heating and cooling mode
changeover. Nuisance trip-outs could occur from
changing modes “on the fly”.
Any number or types of thermostats, aquastats, or
switches can be used with an independent power supply
(typically a 24-volt transformer) to activate specific zone
controls. These zone controls are normally either a zone
pump (Figure 4) or zone valves (Figures 3 and 6). End
switches on the zone valves can be used to pass a signal to
a pump relay when the zone valve is open. The pump
relay then activates a common pump, which supplies any
number of zones. Example: the fan coil in Figure 4 could
be supplied by the same pump as the radiant floor system
if zone valves were used instead of two pumps.
)Note: A common maximum aquastat setpoint is 115
o
F
(with a 15
o
F differential). The tank will then shut down
when it reaches 115
o
F, however, the leaving water
temperature from the heat pump is actually 130
o
F (the
maximum operating temperature). The aquastat
maximum setpoint should limit the head pressure of the
heat pump to 325 psi.
If a thermostat is equipped with an anticipator it should be
set to its maximum setting to avoid interfering with heat
pump operation. The anticipator is a resistor in the
thermostat that heats up as current is drawn through and
satisfies the thermostat prematurely. This reduces system
capacity by restricting run time.
C. Controller
The controller receives a signal from the thermostat and
initiates the correct sequence of operations for the heat
pump. The controller performs the following functions:
1) Earth Loop Pump Initiation
2) Compressor Operation
3) 4-Way Valve Control
4) Compressor Lockouts
5) Compressor Anti-Short-Cycle
6) System Diagnostics
1. Earth Loop Pump Initiation
If a PumpPAK is used, it should be wired directly to the
contactor of the compressor. If a PumpPAK is not
used, a separate pump can be used which is energized
with a pump relay (Note: electrical code will require a
fused disconnect for pumps other than PumpPAKs).
When there is a call for an M1 output from the controller,
the contactor will energize, starting the compressor and
earth loop pump.
2. Compressor Operation
A Y1 signal from the thermostat will ask the controller to
initiate heating or cooling. The controller then decides,
based on lockout and anti-short-cycle periods, when to
bring the compressor on. The M1 output of the controller
energizes the compressor. This compressor stays on until
on the thermostat is satisfied.
3. 4-Way Valve Control
The controller energizes the 4-way reversing valve to
direct the flow of refrigerant. When the thermostat calls
for cooling on the O terminal, the controller energizes its
O output to send control power to the reversing valve
(VR), to switch the refrigerant circuit to the cooling
mode.
4. Compressor Lockouts
A compressor lockout occurs if the high-pressure, low
pressure, or freeze protection pressure switches open.
The controller blocks the signal from the thermostat to the
contactor that normally would energize the compressor. In