Sequence Of Operation - Hussmann Proto-Aire EZ Manual Del Usuario

Proto-Aire EZ I/O Manual
1) General Overview of Sequence
A. System Inputs & Control
The BAS or system controller monitors system inputs, controls system outputs, and provides
alarm functionality, with electro-mechanical or electronic safety devices serving as back
up should the controller fail. The unit shall be configurable for the refrigerants of R404A,
R407A, R407F, R448A, and R449A.
B. Compressors
Compressor staging shall be achieved thru a control point (suction pressure setpoint)
located in the corresponding return suction header. Compressors are operated under the
direction of the rack controller, having outputs wired in series with individual compressor
safety devices – including a compressor high-pressure switch for high discharge pressure
protection, low pressure control for backup safety and/or low suction pressure protection,
and other electronic safeties for individual compressor oil differential pressure and/or oil-level
monitoring. The compressor safety devices provide emergency compressor shut-down and/or
backup to the unit controller.
C. Condenser
Condenser operation is based on a discharge pressure control strategy. The BAS or system
controller operates the condenser fans and will stage/cycle all the fans (#1, #2 & #3) in order to
maintain head pressure.
Condenser fan #1 will be the first fan to turn on and the last to turn off.
Condenser fans #2 & #3 will cycle as required to maintain head pressure during low
ambient conditions. Condenser fans #2 & #3 will be programmed for "round robin"
equal run time.
2) Compressor Safeties
A. Oil Level Failures
Each scroll compressor features the OMC optical oil level control which shall monitor and
maintain proper oil level at the compressor. In the event of low oil level conditions, following a
two-minute internal delay, the oil control shall signal an oil failure condition, and de-energize
the compressor control circuit.
B. High Pressure Lockout Switch
Each compressor includes an automatic reset high pressure switch that, in the event of an
overpressure event at the individual compressor, shall disable the compressor control circuit.
The high-pressure switch will automatically reset when the pressure has dropped below the
switch differential (cut-in) setpoint.

Sequence of Operation

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