Manual Heat Pump Model HHPM-V.2- SEP 2012
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5.5. Time Delay Relay
Time delay relay is provided in the heat pump electrical control circuit to prevent
compressor short cycling. Compressor short cycling is when the compressor attempts to start too
often in a short period of time. The result of this frequent starting will overheat the compressor
motor windings because of insufficient runtime. This function is accomplished by delaying the start
(on-delay) of the compressor for 5 minutes after the last compressor stop. After receiving an
aquastat run signal, the compressor will start promptly.
The factory settings should not be changed. Decreasing the time for the on-delay function will
adversely affect compressor operation.
5.6. Heat Pump Safety
Refrigerant system:
The refrigerant system has safety cutout sensor which will prevent the heat pump from
running In the following cases:
Low Pressure Cutout - Stops the heat pump when refrigerant suction pressure decreases to 20
Psig. The switches normally open contacts close to energize a latching relay. This relay de-
energizes the main contactor.
High Preasure Cutout - Stops the heat pump when refrigerant discharge pressure increases to
350 Psig. The switches normally open contacts close to energize a latching relay. This relay de-
energizes the main contactor.
Resetting the unit:
The above conditions generally indicate that the heat pump needs attention from a
qualified service technician.
Electrical:
Protection for under voltage, over voltage is provided in the control board.
5.7. Temperature control
Two-way modulating valve together with heat pump controller and temperature sensor are used to
adjust the outlet hot water temperature. Temperature sensor is connected to the hot water outlet piping and
send temperature signal to the controller. The controller is electronic temperature controller with PID
function. Two-way modulating valve installed at pump discharge will adjust the water flow rate as response
from the controller to make hot water at the setting temperature. The hot water outlet temperature will always
be at 55-65
o
C from the start of the unit, so hot water can be used quicker.
