Scholar V VAIVA Maintenance & Service Manual 10/2017 Rev.2
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j. Forward
: Press once to go to the next screen.
k. Back
: Press once to go to the previous screen
l. Back to Main
: Press once to go back to Main Screen
8. SCREEN 8: Defrost Settings
(Changes require username/password)
All air source heat pumps require a defrost cycle in the heating mode. As the unit runs in
heating and extracts heat from the outside air, which may be well below 50°F, ice will often
accumulate on the outside coils. A defrost cycle is required to melt this ice periodically.
Thermocouples are embedded in the refrigeration distributor coils of the outside coil. These
tubes are essentially at the refrigerant temperature inside the tubes of the coil. When the
temperature of one of the thermocouples reaches a particular set point, the defrost cycle
in initiated. The reversing valve changes and allows hot gas to enter the outside coil which
removes the ice. During this cycle, the outdoor fan(s) or blower(s) turn off to maximize the heat
forced into the coil.
a. Defrost Run Time (min)
: This is the maximum time that the unit will run in a
defrost cycle.
b. Defrost Reinitiate time (min)
: This time must elapse before another defrost
cycle occurs. It is measured in the run time of the compressor since the end of the
previous defrost cycle.
c. Defrost On Temperature (°F)
: This is the temperature of either of the two outside
coil thermocouples (See Screen 2, Temperatures). A defrost cycle will begin when
either thermocouple reaches this value.
d. Defrost Off Temp (°F)
: This is the temperature at which the defrost cycle
terminates. If the run time expires before the off temperature is reached, the
defrost cycle will terminate. Another cycle will not be attempted until the Reinitate
Time expires.
e. Heat On Defrost
: Press this button once to enable electric resistance heat
operation during a defrost cycle to keep cold air from being introduced into the
room. It is indicated by a 1 in the box at the bottom of the screen.
