AIR COOLED CHILLERS
TROUBLESHOOTING GUIDE
30
Compressorand UnloaderStaging
A one compressor unit has 2 stages, two compressor unit has 4 stages and a four compressor unit has 8 stages. The
odd numbered stages turn compressors #1 ON or OFF while the even numbered stages de-energized the unloader. The
staging of a standard unit is shown in the following chart:
Number of Compressors
Stage
1
2
3
4
5
6
7
8
1
1
*
1
2
1
*
1
1
*, 2
1
, 2
4
1
*
1
1
*, 2
1
, 2
1
*, 2, 3
1
, 2, 3
1
*, 2, 3, 4
1
, 2, 3, 4
*
Indicates that compressor #1 is unloaded
1) No LED display lit or erratic display behavior
a) Check serial cable integrity.
b) Check serial cable connections on both the User Interface Board and the Main Board.
c) Check correct and tight insertion of jumpers JU1 and JU2 on the Main Board.
d) Check correct and tight insertion of jumpers TU1 and TD1 on the User Interface Board and on the last board of the
network.
2) Controller does not respond to keypad
a) Check serial cable integrity.
b) Check serial cable connections on both the User Interface Board and the Main Board.
c) Check correct and tight insertion of jumpers TU1 and TD1 on the User Interface Board, main and/or auxiliary
board.
d) Check dip switches and integrity on the User Interface Board.
3) Several analog values reading incorrectly
a) Check correct and tight connection of the probes to the board.
b) Check the probe cable: test for short-circuit.
c) The pressure transducer probe is a 4-20mA transmitter check the polarity of the connection on the Board.
d) Check if the power supply voltage is into the specified limits: 24Vac +/- 10%.
e) The temperature probe is a PTC sensor disconnect it from the board and measure its resistance that is 1000 ohm
at 25
0
C or 1200 ohm at 50
0
C.
4) Digital input reading incorrectly
a) Check if the auxiliary 115 Vac voltage is present in the electrical box.
b) Check if the AC input on the Board is correctly connected to one of the 115 Vac terminals in the electrical box.
c) Check if A1/A14 inputs are correctly connected with respect to the cabling diagram of the electrical box.
5) No LCD display lit or erratic display behavior
a) Check serial cable integrity.
b) Check serial cable connections on both the User Interface Board and the Main Board.
c) Check correct and tight insertion of jumpers JU1 and JU2 on the Main Board.
d) Check correct and tight insertion of jumpers TU1 and TD1 on the User Interface Board, main and/or auxiliary
board.
e) Adjust display intensity by rotating trimmer RV1 counter-clockwise (from the back side of the board).
