Bi4 And Bi5: High/Low Pressure Cutout; Compressor Contactor Monitoring - Trane Tracer ZN511 Installation And Operation Manual

Chapter 4 Applications for the heat pump configuration
16

BI4 and BI5: High/low pressure cutout

The function of high- and low-pressure cutout is to protect the refrigerant
circuit from abnormal pressure conditions by locking out (disabling) the
compressor operation. Binary input 4 (terminals BI4 and V4) is used to
lock out the first compressor and binary input 5 (terminals BI5 and V5) is
used to lock out the second compressor. Upon an enable-compressor
request, the controller waits 4 seconds before checking the status of BI4
or BI5. After that, the input must close (sense 24 Vac) to operate nor-
mally. If the input opens for more than 200 ms, a High/Low Pressure Cut-
out diagnostic will be generated for that compressor, and it will be locked
out.
Note:
BI4 and BI5 must have 24 Vac applied to them for the control-
ler to allow heat pump operation. For this reason, an electrical
jumper is factory installed between BI4 and V4, and between
BI5 and V5. Terminals V4 and V5 supply 24 Vac for inputs BI4
and BI5, respectively. If either compressor contactor monitoring
or line-voltage monitoring are used, the jumpers must be
removed from the terminal strip. If neither is used, the jumpers
must remain in the terminal strip for proper operation. If jump-
ers are used, no High/Low Pressure Cutout diagnostics will be
generated. However, units with a safety circuit containing high-
and low-pressure switches will continue to protect against
abnormal pressure conditions.
These inputs can be used in one of three ways:
To monitor the compressor contactor
•
To monitor compressor line-voltage
•
To directly monitor the high and low pressure switches
•

Compressor contactor monitoring

By connecting BI4 to the first compressor contactor (see Figure 5 on
page 17), the controller will monitor (indirectly) the high/low pressure
safeties by monitoring the state of the compressor contactor. When the
refrigerant circuit experiences an abnormal pressure condition, the high-
or low-pressure cutout switch will trip the lockout relay, causing the com-
pressor contactor to de-energize. This will result in the controller generat-
ing a High/Low Pressure Cutout diagnostic. BI5 will perform the same
function for the safety circuit of the second compressor.
Note:
With the compressor contactor monitoring option, the controller
will generate a High/Low Pressure Cutout diagnostic when any
safeties, including the freeze-protection switch and the conden-
sate overflow switch remaining in the safety circuit, trip the
lockout relay.
CNT-SVX06B-EN