McQuay AGR 070AS User Manual

86 AGR 070A through 100A IOMM AGR-1
Test Procedures
Status LED Diagnostics
The MCB status LED indications can aid in controller diagnostics. If the status LEDs do not operate
normally there is a problem with the MCB. Following are troubleshooting procedures for the various
symptoms.
Red LED Remains On
If the red LED remains on after the 5-second self-test period, it is likely that the MCB is defective.
However, this can also occur in some instances if there is a power supply problem. Refer to
“Troubleshooting Power Problems” below.
Red and Green LEDs Off
If the red and green LEDs do not turn on after power is applied to the controller, there is likely a
defective component or a problem in the controller’s power distribution circuits. Refer to
“Troubleshooting Power Problems” below.
Troubleshooting Power Problems
The MCB receives 18 Vac, center-tapped power from transformer T4. It then distributes both 5 Vdc
and 13 Vdc power to various MicroTech components. A problem that exists in any of these
components can affect the MCB and thus the entire control system. Power problems can be caused by
an external short, which can blow a fuse, or a defective component, which can either blow a fuse or
create an excessive load on the power supply. An excessive load can lower the power supply voltages
to unacceptable levels. Use the following procedure to isolate the problem. Note that this procedure
may require two or three spare MCB fuses. Refer to the panel wiring diagram.
1.
Verify that circuit breaker CB1 is closed.
2.
Remove the MCB Power In connector and check for 9 Vac between the terminals on the plug
corresponding to terminals 2 and 3 on the board. Then check for 9 Vac between the terminals on
the plug corresponding to terminals 1 and 3 on the board. (Readings of 9–12 Vac are acceptable.)
If 9 Vac is present between both sets of terminals, go to step 3.
If 9 Vac is not present between both sets of terminals, check transformers T2 and T3 and all
wiring between the 115 Vac source and the Power In plug.
3.
Remove power from the controller by opening circuit breaker CB1. Check the MCB power
supply input fuses (F1 and F2) with an ohmmeter. A good fuse will have negligible resistance
through it (less than 2 ohms).
If either or both fuses are blown, replace them. Go to step 4.
If the fuses are intact, the MCB is defective.
4.
Reconnect the Power In connector and disconnect all other connectors on the MCB. Cycle
power to the controller (close and then open CB1) and check the power fuses.
If both fuses are intact, go to step 5.
If either fuse blows, the MCB is defective.
5.
Reconnect the keypad/display ribbon cable. Cycle power to the controller and check the power
fuses.
If both fuses are intact, go to step 6.
If either fuse blows, check the keypad/display and the connecting ribbon cable for shorts. Either
one may be defective.

McQuay AGR 070AS Specifications

General

Brand	McQuay
Model	AGR 070AS
Category	Chiller
Language	English