16 | Sequence of Operation LM Series Heat Pump
LM Series Heat Pump8 733 905 315 (2013/9) Subject to change without prior notice
DPS Water Flow Proving
The DPS water flow proving switch is a factory
installed option available for the LM series. The
DPS prevents compressor operation if there is
inadequate water flow through the water to
refrigerant heat exchanger in the heat pump.
The DPS operates by monitoring the water side
pressure drop across the water to the refrigerant
heat exchanger. When the pressure drop between
the water in and water out lines reaches a pre-set
value, compressor operation is enabled.
Valve End Switch
The leaving water valves are all equipped with
Valve End Switches (VES) and it is a factory
installed option available for the LM series.
The VES prevents compressor operation if the
valve is not fully open. This prevents short-cycling
due to low water through the water-to-refrigerant
heat exchanger in the heat pump.
The VES only closes once the leaving water valve is
fully open. The valve is activated by the
compressor call (Y1) signal.
Pump Relay
The factory installed pump relay can be used to
energize a supply pump or solenoid valve when
there is a call for compressor operation. This relay
can be used to switch either high or low voltage
power.
SEQUENCE OF OPERATION
Cooling Mode
Energizing the “O” terminal energizes the unit
reversing valve thus placing the unit into cooling
mode. The fan motor starts when the “G” terminal
is energized.
When the thermostat calls for first stage cooling
(Y1) the loop pump or solenoid valve if present is
energized and the first stage of compressor
capacity starts.
When the thermostat calls for second stage
cooling (Y2) the second stage (or full compressor
capacity) is initiated. The fan ramps up to full
cooling air flow.
Once the thermostat is satisfied, the compressor
shuts down and the fan ramps down to either fan
only mode or off over a span of 30 seconds.
Heating Mode
The first two stages of heating (Y1 & Y2) operate in
the same manner as cooling, but with the reversing
valve de-energized. On a call for auxiliary heat
(W1), the fan ramps up to auxiliary heat air fl ow
immediately and the electric heater package is
energized along with the compressor. As the
thermostat is satisfied, the heaters will shut off as
soon as W1 is de-energized, and the compressors
will remain on until the thermostat stages are
satisfied.
Once the thermostat is satisfied, the compressor
shuts down and the fan ramps down either fan only
mode or off over a span of 30 seconds. If
thermostat has two different output points one for
Auxiliary heat and a different one for Emergency
heat the two outputs must be terminated on W1
units equipped with one stage of Electric heat.
(Figure #14)
The fan motor will take 30 seconds to ramp up
to operating speed and will run at fan only rated
air flow, as long as there is no call for
compressor or heater operation.
Some options will have a built in delay, and
hence, compressor operation is not immediate.
See ‘Options’ section for more detail.
A fault condition initiating a lockout will de-
energize the compressor irrespective of which
stage is engaged.
If the unit compressor lock out for any reason at
this time, the electric heaters will continue to
function normally.
When using a 2-cool, 3-heat thermostat both the
W1 & W2 on the Heat Pump and W2 & EM on
the thermostat must be connected together via
a jumper. (See Figure#22)
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