036-21342-002 Rev. E (0505)
2
Unitary Products Group
SYSTEM OPERATION
This heat pump model is equipped with both YorkGuard V
heat pump control and TS compressor control. The interface
control 6CF board is used to bypass the first stage of heat
when the outdoor temperature falls below certain tempera-
tures. The TS control board is used only to switch between 1
and 2 cylinder operation. The fault codes and pressure switch
on the TS control board are bypassed using the jumpers
between the test and "PS" pins.
1.
Anti-short Cycle Timer
The five-minute time delay on YorkGuard V will be used
to prevent the system from short cycling after the ther-
mostat off or power interrupt. This time delay can be
bypassed by temporarily shorting the test terminals on
YorkGuard V for 3 seconds. Since a jumper was factory
installed across the test pins on the TS control board, the
anti-short cycle timer on the TS control board is
bypassed.
2.
First Stage Cooling
This heat pump model is equipped with a Twin-Single
compressor. With a call for first stage cooling, the com-
pressor operates one cylinder. The run winding (R) is
connected through the upper left contactor (A) and to the
capacitor and the start winding (S) is connected to line
voltage. The system operates at low discharge pressure
and high suction pressure.
3.
Second Stage of Cooling
With a call for second stage cooling, the TS control will
shut the compressor off for two seconds then energize
relays R1 and R2 on the TS control board. This will de-
energize (open) the upper left contactor (A) and energize
(close) the lower right contactor (B), connecting the com-
pressor run winding (R) to the line voltage and start
winding (S) to the capacitor. The compressor runs in the
reverse direction with two cylinders compared to the first
stage. The system will operate with two cylinders until
both first and second stage are satisfied. The Y2OUT
signal from the relay board causes the indoor blower to
function at high speed.
If the room thermostat calls for second stage cooling
(Y2) on two consecutive cooling cycles, the next call for
cooling for either first or second stage will energize the
unit in second stage mode. The above mode will be reset
to permit start up on the first stage with only a Y1 call
when the second stage operation cycle runs less than 15
minutes or when 24V to the TS control board is discon-
nected.
4.
6K Relay on the 6CF Control Board
The 6K relay on the 6CF interface board operates as fol-
lows. See Figure 1:
a.
If the YorkGuard V defrost control balance point set-
ting is 45°F, the 6K relay will be:
• Energized if liquid temperature goes below 35°F.
• De-energized if the liquid temperature goes above
35°F AND the ambient is greater than 42°F for five
minutes AND the unit is not in defrost.
b.
If the YorkGuard V defrost control balance point set-
ting is at anything but 45°F, the 6K relay will be:
• Energized if liquid temperature goes below 45°F.
• De-energized if the liquid temperature goes above
45°F AND the ambient is greater than 55°F AND
the unit is not in defrost.
5.
Heating mode with the de-energized 6K relay
The TS compressor operates similar to the first and sec-
ond stage of cooling modes except there is no O input
from the thermostat, the reversing valve is not energized,
and the system operates in heating heat pump mode.
The YorkGuard V control and the liquid temperature will
not allow the system to go into the defrost mode.
6.
Heating mode with the energized 6K Relay
The energized 6K relay on the interface board (6CF) will
connect Y1 and Y2 and disconnect Y2OUT from the TS
control to the indoor blower if the J1 pin is not in the ON
position. The compressor will operate only in second
stage regardless of the first or second stage call from the
thermostat. The indoor blower will operate in low air
mode. The indoor discharge air temperature should be
about 10°F hotter than a normal heat pump. If high-
speed air is preferred, move J1 pin to the ON position at
the interface board (6CF). This will send the Y2OUT sig-
nal back to the indoor blower for the high speed air.
FIGURE 1 : 6CF Interface Board
Y2
Y2 OUT
6K
NC
6K
NC
J1
6K
NO
R
Y2
Y1
Y2 OUT
24V (R) FROM
YORKGUARD
