McQuay ACZ 045A, Installation, Operation And Maintenance Manual

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96 IOMM ACZ/AGZ-1
2. Remove power from the controller by placing CB1 to the OFF position. Disconnect at least one
wire from the power input terminals of the Output Board. The resistance should not be less than
3000 ohms.
If the resistance is greater than the acceptable value, go to step 3.
If the resistance is less than the acceptable value, the Output Board is defective.
3. Check the discrete wiring and connections between the Output board and the Controller.
Aux/Out terminal strip and the field wiring terminal strip.
Note: The MCB Aux/Out connector plug terminals displace wire insulation to make contact
with the conductor. If a faulty Aux/Out connection is suspected, try pressing down on the wire
in the terminals with a small screwdriver.
LED Lit, Output not Energized
If the LED of a suspect output is lit but the load connected to it is not energized, and everything is
intact between the MCB and the coil side of the relay, perform the following procedure to isolate the
problem:
1. Verify that 24 or 120Vac power is present at the suspect output’s screw terminal on the Output
Board.
2. Remove power from the controller by opening CB1. Pull the 5-amp fuse on the contact side of the
relay and check it for continuity with an ohmmeter.
If the fuse is not bad, reinstall it and go to step 3.
If the fuse is bad, replace it and inspect the load and associated wiring before restoring power.
Note that a fuse from an unused output can be substituted for the bad fuse.
3. Remove power from the controller by opening CB1. Swap the suspect relay with a known good
relay. Try to choose a relay that will not affect unit operation. Restore power by closing CB1.
If the output load energizes, the suspect relay is bad. Replace the relay.
If the output load does not energize (when LED is lit again), check the load circuit wiring and
components.
Output Energized, LED not Lit
If the LED of a suspect output is not lit, but the load connected to it is energized, either the Solid-State
relay or the MOV is bad. The Solid-State relay contacts and the MOV, which are in parallel, can both
fail closed. Perform the following procedure to isolate the problem:
1. Remove power from the controller by opening CB1. Pull the Solid-State relay from the suspect
output’s socket.
2. Restore power by closing CB1.
If the output load remains energized when there is no relay in the socket, the output’s MOV has
failed and the Output Board must be replaced.
If the output load de-energizes, the relay that was pulled is defective.
Contact Chatter
Contact chatter is very rapid opening and closing of contacts. It is usually caused by low voltage at
the electromechanical relay or contactor coil. If contact chatter is occurring on a relay or contactor
connected to one of the Output Board Solid-State relays, it is also possible that a faulty connection
exists on the power supply terminals of the Aux/Out plug connector on the MCB. In very rare
instances, contact chatter can be caused by a faulty Solid-State relay. Perform the following procedure
to isolate the problem.
1. Verify that the voltage at the load’s power supply and at the Solid-State relay contacts is
adequate.
2. Remove power from the controller by opening CB1. Swap the suspect relay with a known good
relay. Try to choose a relay that will not affect unit operation. Restore power by closing CB1.
If the chatter does not stop, go to step 3.
If the chatter stops, the suspect relay is defective. Replace the relay.