Operation; Unit Protection Module (Upm); General Description; Features And Safeties - Carrier Omnizone 50BV020-064 Installation, Start-Up, Service And Controls Operation And Troubleshooting

OPERATION

Unit Protection Module (UPM)

GENERAL DESCRIPTION

The Unit Protection Module (UPM) as shown in Fig. 36 is a
printed circuit board (PCB) included in all units, that interfaces
with the thermostat for constant volume units or the digital direct
controller on variable air volume units.
The main purpose of this device is to protect the compressors by
monitoring the different states of switches and sensors of each re-
frigerant circuit. This device provides time delays and protects the
unit against freezing of the water and refrigerant heat exchangers
as well as condensate overflow when the appropriate sensors are
installed.

FEATURES AND SAFETIES

Alarm output is Normally Open (NO) dry contact. If 24 vac output
is needed, R must be wired to the ALR-COM terminal; 24 vac will
be available on the ALR-OUT terminal when the unit is in alarm
condition. If pulse is selected, the alarm output will be pulsed.
Power Random Start-Up
This feature prevents multiple units sharing same electrical circuit
or network from starting at the same time. It assures that units
sharing the same electrical circuit do not demand high inrush cur-
rents simultaneously when starting back up after a power failure.
If the controller has been completely powered down for more than
28 milliseconds, a random delay is initiated. If the controller is set
to normal operation (test switch set to NO), then typically the unit
will start within the time range of 270 to 300 seconds.
In order for the random sequence to initiate the unit power must be
removed completely.
IMPORTANT: If the board is set to "TEST" mode through the
"TEST" DIP switch, SW1 delay will be 10 seconds.
Anti-Short Cycle Delay
This feature protects the compressor short cycling if the Y call is
set and removed. The anti-short cycle delay is 300 seconds on
break during normal operation.
NOTE: If the board is set to test mode through the "TEST" DIP
switch, the delay will be 5 seconds.
Fig. 36 — Two-Stage Unit Protection Module
50
High and Low Pressure Protection
The UPM monitors the state of the high and low pressure switch
inputs of each refrigerant circuit, HP1, LP1, HP2, and LP2. These
switches must be closed for the controller to energize the compres-
sor output (CC1 and CC2). The CC output will only be energized
when the switches are closed and the anti-short cycle (and/or ran-
dom start-up when applicable) has expired.
High Pressure Protection
If the HP1 or HP2 switches are open upon a Y1 or Y2 call, the
UPM will not energize the respective CC1 or CC2 outputs; the
corresponding compressor will remain off, the fault LED will
flash 1 time for the HP1 and 3 times for HP2, and the alarm con-
tact will remain off.
If a compressor is running in normal mode on a Y call (Y1 or Y2
or both) and the high pressure switch opens, the UPM will shut
down the compressor output and will keep it off until the switch
closes and the anti-short cycle has expired. The controller will
keep track of the number of times the switch opens; if, within a
1-hour period, the switch opens the number of times set via the
DIP switch, the controller will shut down the compressor and per-
form a hard lockout condition. Under this condition the alarm con-
tact will be energized.
The UPM allows the user to configure the counts that the HP will
be allowed to open within 1 hour before the UPM performs a hard
lockout on the compressor. The user can select either two or four
times by changing switch 4 on the DIP switch SW1 on the UPM
board.
Low Pressure Protection
If the LP1 or LP2 switches are open upon a Y1 or Y2 call (Y1 or
Y2 or both) the UPM will not energize the CC1 or CC2 outputs;
the corresponding compressor will remain off, the fault LED will
flash two times for the LP1 and 4 times for the LP2, and the alarm
contact will remain off.
If the compressor is running in normal mode on a Y call (Y1 or Y2
or both) and the low pressure switch opens, the UPM will keep the
compressor running for 2 minutes. If the condition remains after
this period of time, the compressor will shut down and the UPM
will start a soft lockout. The UPM will flash 2 times for the LP1
and 4 times for the LP2 and the alarm contact will remain off.
If the switches close, the UPM will start the compressor after the
anti-short cycle has expired and UPM will energize the compres-
sor output.