APC ACRD101 User Manual

Cooling unit does not 
shut down on 
command

• Drive voltage

• Verify that there is a drive voltage entering the input of the 

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

• Verify Customer Input Contact settings. See “Contacts” on 

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 100-ohm resistor (a 
terminating resistor of 100 to 120 ohms).

Cooling units are not 
communicating with 
each other

• A-Link failure

• Verify 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.