Mydax, Inc. 1M9W-S Water Cooled Chiller
Lawrence Berkeley Laboratory 8
DIAGNOSTIC DISPLAYS
Mydax chillers are provided with a computerized self-diagnostic capability. This system is equipped with 9 different
test panels, which are accessed by pressing the TEST key, followed by the test panel number. Diagnostic mode is
terminated by pressing the CLEAR key, and results in a display similar to that below:
MAIN DISPLAY
Diagnostic messages are displayed on the main 2 by 40-character LCD. Display #5 automatically appears when the
TEST key is first depressed. Once in diagnostic mode, other displays can be selected by depressing number keys 1
through 9. The following describes each of the test displays:
TEST PANEL #1:
Numbers represent the drive signals for the evaporator valve and tank heater. The range is 0 (minimum) to 20
(maximum drive). Each digit represents 5% of the available 24VDC drive voltage. Avg Valve shows a 32
second running average of the valve's drive, displayed above it.
TEST PANEL #2:
This display shows the refrigerant circuit RTD temperatures in °C. The display reads:
Limit = Max Evaporator Temp
Suct = Suction Temp
Psig = Suction Pressure
Sup.Ht = Superheat Temp
SHavg = Avg Super Ht Temp
Cond = Condenser Temp
The condenser reading is a direct indicator of condenser temperature and pressure. The microprocessor sends
the CONDENSER HOT error message if the condenser temperature e54°C.
TEST PANEL #3:
The first 3 sets of 4-digit numbers are hexadecimal. They represent correction values for the slow gain servos
for up to 3 reservoirs. The function of this servo is to dynamically adjust the main temperature control servo
to near zero error and thereby maintain temperature stability.
The first 2 digits in each set of 4 show the gain offset. Each increment equals 0.05°C, so 14 Hex = 20 decimal
= 1.0°C. This value is internally subtracted from the operator-entered temperature setpoint if the actual
temperature is above the setpoint, thus reducing the coolant temperature. When the actual coolant temperature
is below setpoint, the main servo is driving a heater and no adjustment is made to the setpoint. The setpoint
offset is continuously monitored by the controller and adjusted according to current conditions.
The second 2 digits in each set of 4 show the time prescaler. This is a counter which increments or decrements
once a second and times the next update of the setpoint offset. A typical value is 20 seconds per offset change.
When the count reaches "00", the offset may or may not be changed and the count resets to "0A" Hex (10
decimal). Together these numbers show that the controller is internally changing the control setpoint to
maintain temperature stability, and give the magnitude and timing of the change.
Output --- MYDAX --- Local Set
20.02°C 20.0°C
Valve 7
Htr 8
Avg Valve 5
Htr 6
4.0 -4.8 48.2 35.0
Limit
Suct Psig Sup.Ht SHavg Condr
302B 0000 091F Z 0.00 G 51.95 14.4
SS-1 SS-2 SS-3 RTD Reference SH Avg
