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IMPORT NT: The compressor has an internal overload protector. Under some condi-
tions, it can take up to 2 hours for this overload to reset. Make sure overload has had
time to reset before condemning the compressor.
Some units are equipped with a time delay control (TDC1). The control allows the blower
to operate for up to 90 seconds after the thermostat is satisfied.
XVIII. AUXILIARY HEAT
The amount of auxiliary heat required depends on the heat loss of the structure to be
heated and the capacity of the heat pump. It is good practice to install strip heat to main-
tain at least 60ºF indoor temperatures in case of compressor failure. The auxiliary heat
is energized by the second stage of the thermostat. The amount of electric heat that is
allowed to come on, as determined by the output of the heat pump, may be controlled by
an outdoor thermostat.
WARNING
ONLY ELECTRIC HEATER KITS SUPPLIED BY THIS MANUFACTURER AS
DESCRIBED IN THIS PUBLICATION HAVE BEEN DESIGNED, TESTED, AND
EVALUATED BY A NATIONALLY RECOGNIZED SAFETY TESTING AGENCY
FOR USE WITH THIS UNIT. USE OF ANY OTHER MANUFACTURED ELECTRIC
HEATERS INSTALLED WITHIN THIS UNIT MAY CAUSE HAZARDOUS CONDI-
TIONS RESULTING IN PROPERTY DAMAGE, FIRE, BODILY INJURY OR
DEATH.
A. CONTROL SYSTEM OPERATION
1. In the cooling mode, the thermostat will, on a call for cooling, energize the com-
pressor contactor and the indoor blower relay. The indoor blower can be operated
continuously by setting the thermostat fan switch at the "ON" position. The revers-
ing valve coil is de-energized.
2. In the heating mode, the first heat stage of the thermostat will energize the com-
pressor contactor and the indoor blower relay. The second heat stage will turn on
one or more supplementary resistance heaters. The reversing valve is energized
except in defrost. If required or considered desirable, the resistance heat may
also be controlled by outdoor thermostats.
XIX. DEMAND DEFROST CONTROL AND
HIGH/LOW PRESSURE CONTROLS
The demand defrost control is a printed circuit board assembly consisting of solid
state control devices with electro-mechanical outputs. The demand defrost control
monitors the outdoor ambient temperature, outdoor coil temperature, and the com-
pressor run-time to determine when a defrost cycle is required.
Enhanced Feature Demand Defrost Control: Has high and low pressure control
inputs with unique pressure switch logic built into the microprocessor to provide
compressor and system protection without nuisance lock-outs. Cycles the compres-
sor off for 30 seconds at the beginning and end of the defrost cycle to eliminate the
increased compressor noise caused by rapidly changing system pressures when
the reversing valve switches. See the end of this section for diagnostic flash codes
for the two diagnostic LED's provided on the control.
DEFROST INITIATION
A defrost will be initiated when the three conditions below are satisfied:
1) The outdoor coil temperature is below 35°F.
2) The compressor has operated for at least 34 minutes with the outdoor coil tem-
perature below 35°F.
3) The measured difference between the ambient temperature and the outdoor
coil temperature is greater than the calculated delta T.
Additionally, a defrost will be initiated if six hours of accumulated compressor run-
time has elapsed without a defrost with the outdoor coil temperature below 35°F.
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