Emerson DH, VH, DE, VE manual Control Circuit Board

Advanced Microprocessor with Graphics Control Setup

4.13.3Compressor Sequencing Control

The lead compressor is the first one to be turned on when compressor operation is required. The lag compressor is turned on second if both compressors are required. The control monitors the operating time of both compressors and will automatically switch lead/lag compressor operation to maintain less than eight hours difference between the running times of two compressors.

When the operating hours on the lead compressor become eight hours greater than on the lag com- pressor, the lead/lag operation is automatically switched. If the lead compressor is operating by itself at that time, it will be turned off, the lead/lag operation will be changed, and the new lead compressor will be turned on.

NOTE

If the hot gas reheat option has been selected, compressor 2 is always the lead compressor.

4.14Control Circuit Board

The control circuit board is located inside the unit behind the LCD display and control key panel. Open the front panel for access to the board.

The control board includes an adjustment for LCD display contrast, nonvolatile memory, DIP switches (which should not require customer changes), control output LEDs and jumpers for board configuration.

The jumpers should be placed as follows:

P5—removed

P12—removed P19—installed, Pins 1 and 2 P47—installed, Pins 1 and 2 P48—installed, Pins 1 and 2

P50—all jumpers installed for 4-20 mA analog inputs. See Table 14 for other configurations P51—removed

4.14.1LCD Display Contrast

The level of contrast due to the viewing angle of the LCD display can be adjusted using a small thumb wheel at the upper left of the control board just under the cable going to the display. The control is labeled R6.

NOTE

The LCD backlighting will turn on when any key is pressed and will go off 5 minutes after the last key is pressed.

4.14.2Nonvolatile Memory

All critical information is stored in nonvolatile memory. Setpoints, setup parameters, and component run hours are kept inside the microcontroller in EEPROM. Information retained for data logging, 24 hour component run hour graphs, alarm history, and the water detection floor plan is kept in non-vol- atile RAM.

4.14.3DIP Switches

Equipment options are selected and enabled using DIP switches 1 to 7. These are located at the upper left of the control board and are labeled SW1. Switch 1 is at the top. These switches are factory set and should not require any user changes. The setting and function of the switches can be read from the LCD display and are also described in more detail in 4.8.4 - DIP Switches.

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