APC ACSC100 User Manual

Local display is not 
operational, but 
cooling unit 
operates

• Local display not connected 

properly

• Verify that the local display cable is connected properly.

Incorrect air 
pressure

• False filter clogs

• Verify that the ends of the clear plastic air tubes are not 

obstructed.

• Verify that the clear plastic air tubes are connected to the 

controller.

• Verify that the clear plastic air tubes are not pinched.

Alarms do not 
display on 
monitoring 
equipment 
(Customer Output 
Contact)

• External monitoring 

equipment is not receiving 
power or is not functioning 
properly

• Confirm that power, if required, is being supplied to the 

external equipment.

• If the cooling unit is providing power (+12 V or +24 V) to 

the external equipment, verify that the external equipment 
is <20 mA.

• Test the external equipment by bypassing the customer 

output contact.

Cooling unit does 
not shutdown on 
command

• Drive voltage

• Verify that there is a drive voltage entering the cooling unit. 

You may use the available +12 V or +24 V power located 
near the cooling unit. You must then also use the ground.

No communication 
with building 
management system 
(BMS) port

• Improper connection

• Confirm that the cooling unit is connected to the BMS port 

and not to the Control port.

• Make sure that the wire polarity is correct. 

Using a DC voltmeter, test the signal with no transmissions 
in progress: Pin 2 should be greater than Pin 1 by at least 
200 mV. Measure the cooling unit with the cable 
disconnected, and then measure it again with the cable 
connected. If the signal is less than 200 mV, the cooling unit 
may be reverse-wired.

• Make sure that every cooling unit has either two sets of 

wires in its connector OR one set of wires and a 150–ohm 
resistor.

Cooling units are 
not communicating 
with each other

• A-Link failure

• Verify that the actual number of cooling units in the group 

matches the group number setting.

• Verify that the A-Link ports of every cooling unit have 

either two cables or one cable and a terminator.

• Confirm that the A-Link cables are connected to the A-Link 

ports and that a network cable is connected to the network 
port.

Output air is 17°C 
(62°F) and fans are 
running at a very 
high rate of speed.

• Upper or lower supply air 

sensor fault

• Either the upper or lower supply air temperature sensor has 

a fault. Verify that both supply air temperature sensors are 
installed and working properly.