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• Upon defrost initiation, reversing valve shifts to Cooling
Mode with outdoor fan Off, indoor blower and optional
electric heat (if available) On. Hot gas from compressor
melts frost and ice on outdoor coil and electric heat
tempers indoor air, until outdoor coil sensor reaches
60ºF (15.5ºC) or 10 minutes has elapsed. System
reverts to normal heat pump operation. Defrost times
vary depending on outdoor temperature, wind, and
moisture conditions.
• In Cooling Mode reversing valve is energized at all
times. When air handler calls for cooling, if compressor
is not in ASCT, it will start softly then increase speed as
necessary to balance indoor cooling load with outdoor
ambient, while minimizing number of compressor
starts and stops. Actual compressor speed is based on
room temperature differential, indoor fan speed, and
compressor rated frequency parameters. Minimum
compressor run times and indoor coil freeze protection
are in place whenever compressor runs in Cooling Mode.
Condenser mounted Electronic Expansion Valve (EXV)
continuously adjusts refrigerant fl ow to maintain 15ºF
(8.3ºC) superheat at compressor. Expanded refrigerant
vapor travels through small diameter tube of line set to
air handler where heat is transferred into refrigerant.
Once refrigerant evaporates, super-heated vapor returns
to condenser via large diameter tube. Refrigerant
expansion occurs in outdoor unit, both tubes in line set
require insulation.
• As temperature of indoor space moves closer to set
point compressor, indoor, and outdoor motors adjust
speeds to reduce rate of indoor temperature change
and avoid passing set point. As temperature of indoor
space moves farther from set point compressor, indoor,
and outdoor motors adjust to increase rate of indoor
temperature change and remain close to set point.
System tries to remain running, minimizing the number
of start / stop cycles. This provides the most uniform
space conditioning comfort levels and best overall
system effi ciency.
• In Heating Mode reversing valve is de-energized, except
during defrost. When air handler calls for heating,
if compressor is not in ASCT, it will start softly then
increase in speed as necessary to balance indoor
heating load with outdoor ambient, while minimizing
compressor starts and stops. Actual compressor speed
is based on room temperature differential, indoor fan
speed, and compressor rated frequency parameters.
Minimum compressor run times and outdoor coil defrost
are in place whenever compressor runs in Heating
Mode. Condenser mounted Electronic Expansion Valve
(EXV) continuously adjusts refrigerant fl ow to maintain
15ºF (8.3ºC) superheat at compressor. Refrigerant
vapor travels through large diameter tube of line set
to air handler where heat is transferred into air. Once
refrigerant is condensed, sub-cooled liquid returns to
condenser via small diameter tube.
SINGLE-ZONE CONDENSER SEQUENCE OF OPERATION
• As temperature of indoor space moves closer to set
point compressor, indoor, and outdoor motors adjust
speeds to reduce rate of indoor temperature change
and avoid passing set point. As temperature of indoor
space moves farther from set point compressor, indoor,
and outdoor motors adjust to increase rate of indoor
temperature change and remain close to set point. If
system has optional electric heat, and heat pump alone
(stage 1) can not reduce set point differential, optional
electric heat energizes (stage 2) of heat. System tries
to remain running, minimizing number of start / stop
cycles. Providing uniform space conditioning levels and
best overall system effi ciency.
Defrost Controls With Short Cycle Protection
(Heat Pumps Only)
Unit is equipped with logic control circuit designed to keep
system operating at peak effi ciency.
24v circuit provides control to indoor and outdoor systems
including three minute, anti-short cycle timer (ASCT)
compressor protection.
Defrost control circuit is designed to keep condenser
coil free from frost and ice during heating mode. This
is accomplished through precise switching sequence of
outdoor fan, reversing valve and optional indoor electric
heater.
Defrost Initiation
1.
Defrost-sensor is located on end plate or return bend
of condenser coil.
2.
Defrost cycle initiates after sensor closes
(approximately 30°F) and remains closed for 90
minutes of compressor run time.
3.
At start of defrost cycle
A. Reversing valve changes from heating to cooling
mode. Condenser fan switches Off allowing
pressure and temperature to rise within condenser
coil to melt any ice build-up.
B. At same time unit switches On optional indoor
electric strip heater to temper cold air being
discharged from air handler.
C. Continues until defrost-sensor opens
(approximately 60°F) or 10 minute maximum cycle
time has elapsed.
D. Defrost times vary depending on outdoor
temperature and moisture conditions.
4.
When defrost cycle is complete unit returns to normal
heating operation.
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