York PHE6B36 Installation Manual page 15

3. When the heating demand is satisfied, the electric heat is de-ener-
gized when the 24 volt "W" signal is removed, and the "M" contactor
is de-energized when the 24 volt "Y" signal is removed.
When the fan switches on the thermostat is in the "ON" position, the
indoor blower continues to run. When the fan switch is in the
"AUTO" position, the indoor blower motor ramps down after the
blower off delay.
4. Refer to Table 13 for more information on electrical heat blower
OFF delay.
DEFROST OPERATION
The demand defrost control implements a temperature differential
("delta-T") demand defrost algorithm. The heat pump is allowed to oper-
ate in the heating mode until the combination of outdoor ambient and
outdoor coil temperatures indicate that defrosting is necessary. When
coil temperature is below the initiate point for the ambient temperature
continuously for 4-1/2 minutes, the heat pump is put into a defrost cycle.
This 4-1/2 minute timer eliminates unnecessary defrost cycles caused
by refrigeration surges such as those that occur at the start of a heating
cycle.
A timed inhibit feature prevents the system from responding to a call for
defrost less than 40 minutes after the initiation of the previous defrost.
After the 40 minute inhibit time has expired, temperature conditions
must call for defrost continuously for 4-1/2 minutes before a defrost
cycle is initiated. A temperature inhibit feature prohibits defrost if the coil
temperature is above 40°F.
FIGURE 8: Demand Defrost Control
Johnson Controls Unitary Products
A forced-defrost feature puts the system into a defrost period every 6
hours and 4 minutes of accumulated compressor run-time to recirculate
lubricants, unless the coil temperature is above 40°F and the ambient
temperature is above 50°F. All defrost timing occurs only while the com-
pressor is on.
During the defrost mode, the reversing valve is energized, the outdoor
fan is de-energized, the compressor is energized, and the defrost con-
trol provides a 24 volt signal from terminal "W1OUT" to energize electric
heat stage 1 if the unit is equipped with electric heat.
By selecting "LO" on the "DEFROST HEAT" jumper, "W1 OUT" is ener-
gized during defrost. By selecting "HI" on the "DEFROST HEAT"
jumper, "W1 OUT" and "W2 OUT" are energized during defrost.
For trouble shooting purposes, the defrost cycle can be manually initi-
ated by shorting the "TEST" pins together for 5 seconds while "Y" is
energized. After removing the short, defrost will terminate normally
during the "TEST" mode.
Table 17: Demand Defrost Selection
Unit
048, 060
036 — 042
036 — 060
*
For extreme environments as necessary only.
5285477-UIM-A-1016
Pin Position
2
3
*
4
15