Emerson 20/20 service manual Cool Compression Control

Section 25 • Cool Compression Control

operational differences that are mostly associated with the compressor safeties:

1.The Cool Compression program ignores,

•Low Oil Separator Alarm / Trip at start

•High Filter Differential at start

•Prelube Oil Pressure Alarm and Trip

•Run Oil Pressure Alarm and Trip (Pressure Ratios are monitored instead).

•High Discharge Temp Alarm and Trip (Discharge Temp Superheat is monitored)

•Low Suction Temp Alarm and Trip

•Low Oil Injection Temp Alarm and Trip

•High Oil Injection Temp Alarm and Trip

2.SOI solenoid is forced on for first 60 seconds of run- ning and 10 minutes after compressor is stopped.

3.Auto Load Enabled: When Auto Load is engaged at start, it then maintains the position of capacity slide to the Auto Load limit (approx : 30 %, but less than 50 %). It displays status message “Cool Compression Capacity Hold” when it is running. Unless Auto load is disengaged compressor will run at auto load limit position. Auto load disengages if enough Pressure Ratio is built (typically more than 2.04) or setpoints are achieved.

4.SOI Solenoid: During normal operation if pressure ra- tio drops to a lower value (typically below 2.00) then it energizes SOI solenoid and maintains the position of ca- pacity slide to the SOI Load limit (approx : 30 %, less than

50%). It also displays status message “Cool Compression Capacity Hold”. If enough Pressure Ratio is built across the compressor (typically more than 2.04), it again re- sumes the run mode and control normally.

5.It performs Cool Compression specific checks periodi- cally like:

•Controlling the liquid level positioning valve as liquid ammonia level changes .

•Low / high Pressure Oil Injection ports control as Pressure Ratio and Superheat temperature changes.

Supplemental Oil Cooling Solenoids

•Some cool compression units will have supplemental oil cooling solenoids. One is called the suction liquid injection solenoid and is controlled via discharge su- perheat. When the discharge superheat reaches 5°F, the solenoid is turned on. When it falls back to below 4°F, the solenoid is turned off. An additional solenoid (referenced as SV4 – as called the High Press Ratio solenoid) provides supplemental oil cooling based on pressure ratio. When the pressure ratio rises above

5.0, the solenoid is turned on. When the pressure ra- tio falls back to below 4.8, the solenoid is turned off.

Level Switches

•There are two level switches in the oil separator, a “high” and a “low”. During normal running opera- tion, the oil level is above both switches. When the oil level starts to drop and opens the high level switch, a 10 minute timer starts. When the timer elapses a flashing “add oil to middle of sight glass” message ap- pears on the main screen. When the operator adds enough oil to close the high level switch, the mes- sage disappears.

NOTICE

If oil is not added and the oil level continues to drop thereby opening the “low” oil level switch, a 10 minute timer starts again. When the timer elapses, the com- pressor shutdowns immediately and displays “Low Oil Level” failure. If enough oil is added to close the low level switch, then this will allow the opeator to press the reset button and clear the “Low Oil Level” failure and “Add Oil” message.

Oil Level Messaging After Compressor Stops

•The low level switch is monitored after the compres- sor stops. If the switch opens after the compressor stops, a two minute timer starts. If the switch stays open, and the timer expires, a failure is generated called “Lo Oil Level Fail after Stop” and the compres- sor is disabled from restarting until oil is added to close the low level switch. Note that this failure is generated ONLY when the low level switch opens af- ter the compressor stops.

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