Service manual

6 – 11

Vission 20/20 • Operation and Service Manual •Vilter/Emerson • 35391SC 2.0

Section 6 • Compressor Control

Figure 6-10. Compressor Control Screen - Misc. 1 (Control Mode)

Control Mode

This drop down box gives the operator the ability to

change the type of control mode such as suction pres-

sure control or process temperature control. The opera-

tor can also switch from setpoint 1 and setpoint 2 for

each control method. What is available in this dropdown

box is dependent on the number and type of control se-

lected in the conﬁ guration screen, see Figure 6-10.

Stop Load and Force Unload

The stop load and force unload feature’s primary pur-

pose is to attempt to prevent the compressor from

tripping off due to particular instrument reading. For

example, if the suction pressure drops too low, the com-

pressor will trip off for safety reasons. However, the stop

load & force unload algorithm recognizes a potential trip

and either stops the compressor from loading up or even

unloads the compressor to prevent the trip.

Stop load:

• When this value is reached, the capacity slide will not

advance in any condition.

Force Unload:

• When this value is reached, the capacity slide posi-

tion will decrease until the variable reading is below

this value.

High Motor Amps:

• Motor current values for stop load and force unload.

High Discharge Pressure:

• Discharge pressure value for stop load and force

unload.

Low Suction Pressure:

• Suction pressure values for stop load and force unload

High Discharge Superheat:

• Discharge temperature superheat values for stop

load and force unload. This is only used for Cool

Compression.