York PHG6A24 Installation Manual page 19

HEAT PUMP HEATING SEQUENCE OF OPERATION
1. On a call for heating, the thermostat sends 24 volts to "Y1" or
"Y1"+"Y2" on the defrost control board. After the anti-short cycle
period is complete, the 24 volt signal from "Y1" energizes contactor
coil "M" to supply power for the compressor and outdoor fan motor.
The indoor blower control operates the indoor blower motor at the
"LOW COOL" speed. If the 24 volt signal from "Y2" is present, the
defrost control board energizes the 2nd stage compressor solenoid
and signals the indoor blower control to operate the indoor blower
motor at the "HIGH COOL" speed. The reversing valve remains in
the heating position. Indoor blower speeds are selected by the
"COOL" jumper on the ignition control board.
2. If the heat pump cannot meet the heating demand using mechanical
(compressor) heating, the indoor thermostat locks out the heat pump
and energizes the secondary gas heating. The room thermostat
sends a 24 VAC signal on "W1" or "W1"+"W2." This brings on
inducer and starts the ignition cycle. The "W1" (or the "W1" + "W2")
signal activates the "LOW HEAT" (or the "HIGH HEAT") airflow speed
on the indoor blower motor.
3. When the heating demand is satisfied, the 24 volt "W1" (or the "W1"
+ "W2") or the "Y1" (or "Y1" + "Y2") is de-energized depending on
whether heating was satisfied using primary or secondary heating
mode.
When the fan switch 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.
Hot Heat Pump Mode
The Hot Heat Pump mode is an optional mode that slows the circulating
air blower in order to provide higher air temperatures at the register and
better comfort. In Hot Heat Pump mode, the compressor runs at HIGH
HEAT speed while the circulating air blower runs at LOW HEAT speed.
To operate the unit in Hot Heat Pump mode, move the "Hot Heat Pump"
jumper on the defrost control board to the ON position. See Figure 9.
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
FIGURE 9: Demand Defrost Control
Heat Pump Safety Switch Operation
Johnson Controls Unitary Products
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.
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. Defrost curve selection maybe switched to pin 4 if a more
aggressive defrost cycle is necessary.
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" or "W1OUT" +
"W2OUT" based on the defrost supplemental heat selection jumper
located on the defrost control board to energize gas heat.
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 15: Demand Defrost Selection
Unit
024 — 060
024 — 060
*
For extreme environments as necessary only.
5322625-UIM-A-0417
Pin Position
2
4*
19