HP - B 4
Control Boards
The switch is wired directly to plug J4 (LPCO) (Figure
7&8) on the Integrated Control Board.
Typical causes of low system pressure include under
charging, refrigerant leaks, lack of air volume, and
refrigerant restrictions in the system.
Figure 6
Figure 7
Cool Mode LPCO Logic
The integrated control board will monitor system pres-
sure and will monitor the LPCO. If it senses an open
LPCO event, it will start a 5 minute wait period where
the compressor is shut off. The Comfort Control will
display Wait and the Integrated Control Board Fault
LED will flash 7 times.
If the LPCO switch closes, the system will re-start the
compressor. This cycle will occur for up to two times.
If the LPCO opens for a 3th time during the call, the
system will lock out and power will need to be cycled
for the system to reset.
When the system locks out on the 3rd event, ERR 79
is displayed on the Comfort Control and a 7 flash is
displayed on the Integrated Control Board (See Figure
5.) Fault LED. If a TAM is enabled, the TAM will dial
out an error message.
Low Temp Lockout in Cool Mode
If the LPCO opens and the Outdoor air temperature is
below 50F, the unit will remain locked out of cooling
operation until the outdoor air temperature reaches 60F.
The Comfort Control will display ERR 79 and the Inte-
grated Control Board Fault LED will flash 7 times. The
TAM will dial out if enabled.
Timing Logic for LPCO Open Events
Graph 2
Graph 1
Figure 8
Low pressure monitor A/C trip points
Low pressure monitor
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