Trane ACONT900AC43UA Service Manual page 51

Figure 2
High Pressure Monitor Logic
All models are high pressure protected with a high
pressure cut off control during any stage of operation.
(HPCO) The HPCO switch (Figure 3.) opens at 650
PSIG and closes at 500 PSIG. The system has two
HPCO switches to monitor both compressor stages.
Figure 3
The switches are wired between the compressor
contactor low voltage solenoid and terminals 1 and 2
of plug J3 on the Integrated Control Board (Figure 4.)
Typical causes of high system pressure include over
charging, dirty condensing coil, lack of air volume in
heat mode, non condensing gasses in the system,
OD fan failure in cooling mode, or ID fan failure in heat-
ing mode.
Figure 4
Control Boards
The integrated control board will monitor system pres-
sure via the Liquid Pressure Transducer and will monitor
the HPCO. If it senses an open HPCO event, will start
a 5 minute wait period where the compressor is shut
off. If the HPCO switch closes, the system will re-
start the compressor. This cycle will continue for up
to 4 times during a call for heat or cool compressor
operation. If the HPCO opens for a 5th time during the
call, the system will lock out and power will need to
be cycle for the system to reset.
When the system locks out on the 5th event, ERR 80
is displayed on the Comfort Control and a 17 flash is
displayed on the Integrated Control Board Fault LED
(Figure 5.). If a TAM is enabled, the TAM will dial out
an error message.
If the HPCO control is defective due to a short or open
condition in the sensor, the High Pressure Monitor
Logic is ignored. A faulty sensor error ERR 113 will
be displayed on the Comfort Control and a 12 flash
will display on the Integrated Control Board Fault LED.
Figure 5
Low Pressure Monitor Logic
All models are low pressure protected with a low pres-
sure cut off control during any stage of operation.
(LPCO) The heat pump LPCO switch opens at 25
PSIG and closes at 45 PSIG. The A/C LPCO switch
opens at 50 PSIG and closes at 70 PSIG. The LPCO
switch (Figure 6.) is monitored during all stages of
operation. (If LPCO is open at power-up, the unit is
locked out of operation.)
HP - B 3