Operating instructions

Electrical Check Out
CAUTION
Electrical power must be applied to the compressor crankcase heaters
24 hours before starting unit to drive off refrigerant from the
oil or compressor damage can occur.
1. Open all electrical disconnects and check all power wiring connections. Start at the power block
and check all connections through all components to and including the compressor terminals.
These should be checked again after 3 months of operation and at least annually thereafter.
2. Check all control wiring by pulling on the wire at the spade connections and tighten all screw
connections. Check plug-in relays for proper seating and that retaining clips are installed.
3. Put System Switch (S1) to the Emergency Stop position.
4. Put both circuit #1 & #2 switches to the Pumpdown and Stop position.
5. Apply power to the unit. The panel Alarm Light will stay on until S1 is closed. Ignore the
Alarm Light for the checkout period. If you have the optional Alarm Bell, you can disconnect it.
6. Check at the power block or disconnect for the proper voltage and for the proper voltage
between phases. Check power for proper phasing using a phase sequence meter before starting
unit.
7. Check for 120Vac at the control transformer and at TB-2 terminal #1 and the neutral block (NB).
8. Check between TB-2 terminal #7 and NB for 120Vac supply for transformer #2.
9. Check between TB-2 terminal #2 and NB for 120Vac control voltage. This supplies the
compressor crank case heaters.
10. Check between TB-3 terminal #17 and #27 for 24Vac control voltage.
Operation
Hot Gas Bypass (Optional)
This option allows the system to operate at lower loads without excessive on/off compressor cycling.
The hot gas bypass option is required to be on both refrigerant circuits because of the lead / lag
feature of the controller.
This option allows passage of discharge gas into the evaporator inlet (between the TX valve and the
evaporator) which generates a false load to supplement the actual chilled water or air handler load.
Note: The hot gas bypass valve cannot generate a 100% false load.
The valve that is supplied can provide a load of approximately 10 tons. The system load added to the
ten tons of the hot gas bypass valve has to exceed the compressor capacity for stage 1 compressors to
produce stable system operation. This requires 3-6 tons of system load.
The MicroTech II controls solenoid valves in the hot gas bypass lines that are energized whenever
their circuit is operating with only one compressor running. The hot gas valve is regulated by the
evaporator pressure and the remote adjustable bulb. The pressure regulating valve is factory set to
begin opening at 58 psig (32°F for R-22).
WARNING
The hot gas line can become hot enough to cause injury.
Be careful during valve checkout.
IMM ACZ/AGZ-4 ACZ / AGZ-BM 61