OMM 1087
AGZ 025D through 190D
39
Freezestat logic allows the circuit to run for varying times at low pressures. The lower the pressure,
the shorter the time the compressor can run. This time is calculated as follows:
Freeze error
= Low Evaporator Pressure Unload – Evaporator Pressure
Freeze time
=
For units equipped with 10 or more condenser fans (shell and tube type evaporator):
80 – freeze error, limited to a range of 40 to 80 seconds
For all other configurations (plate to plate type evaporator):
60 – freeze error, limited to a range of 20 to 60 seconds
When the evaporator pressure goes below the Low Evaporator Pressure Unload set point, a timer starts.
If this timer exceeds the freeze time, then a freezestat trip occurs. If the evaporator pressure rises to the
unload set point or higher, and the freeze time has not been exceeded, the timer will reset.
The alarm cannot trigger if the evaporator pressure sensor fault is active.
Action Taken:
Rapid stop circuit.
Reset:
This alarm can be cleared manually via the keypad if the evaporator pressure is above 137.9
KPA (20 PSI).
High Condenser Pressure
Trigger:
Condenser Pressure > High Condenser Pressure set point
Action Taken:
Rapid stop circuit
Reset:
This alarm can be cleared manually via the controller keypad
Mechanical High Pressure Switch
Trigger:
Mechanical High Pressure switch input is open, Motor Protection input is closed, and power
up start delay is not active.
Action Taken:
Rapid stop circuit.
Reset:
This alarm can be cleared manually via the controller keypad if the MHP switch input is closed.
Motor Protection Fault
Trigger:
Motor Protection input is open and power up start delay is not active.
Action Taken:
Rapid stop circuit.
Reset:
This alarm can be cleared manually via the controller keypad if the input is closed.
Low OAT Restart Fault
Trigger:
Circuit has failed three low OAT start attempts.
Action Taken:
Rapid stop circuit.
Reset:
This alarm can be cleared manually via the keypad or via BAS command.
Summary of Contents for McQuay AGZ-D
Page 12: ...12 AGZ 025D through 190D OMM 1087 Figure 2 Typical Field Control Wiring...
Page 71: ......
Page 79: ......
Page 81: ......