Rev 3.1 01/11/23 - 24 - Model 600 User Guide
6.10 HVAC Mode
Holding register 106 is used to enumerate the current control mode of the HVAC systems. For example,
a value of 4 equals econ 1 mode. Writing to this register will override the current control mode and
force the HVAC units to a specific control mode. Writing to this register requires two pieces of
information. The high byte is the number of minutes for the bypass and the low byte is the desired
mode. For example, if you want to bypass to cool 2 mode for 60 minutes then you would write the
value 15366, which is calculated as follows:
High byte Hex value of minutes + low byte Hex value of mode = The register value in Hex. Then convert
the value to decimal.
60 minutes = 3c hex + 06 for Cool 2 mode = 3c06 hex which equals decimal 15366.
Tip: you can use the built-in Windows calculator in programmer mode to do the calculations.
The Model 600 will countdown and return to automatic mode at the end of the bypass time.
Alternatively, you can write a 0 to the register to clear the bypass.
6.11 Remote Alarm Monitoring
The Model 600 has built-in alarm monitoring functions to determine when an alarm condition is present
and will display the alarm on the front panel as well as making the corresponding register have a value
of 1. Registers 200-210 contain the available alarm status points. Writing any value to the register will
clear the alarm condition which will change the register value to 0 and clear the message from the
display. The alarm will not occur again until the problem clears and occurs again.
7 Troubleshooting
LCD Screen is dark and no characters are
displayed
Verify power is present from each HVAC unit between the R
and C terminals. Also verify the DC power input if being
used.
Controlling Sensor reads OER or SER
The zone sensor(s) used for controlling the HVAC unit are
either shorted to ground (SER) or are open (OER). Check the
wiring and terminations for possible shorts or broken
connections. Note if no sensor is terminated to Zone 2 (the
remote sensor) then it is normal for the reading to be OER
for the input. If the controlling sensor reads OER then make
sure Z2 is not chosen as the sensor for control when it is not
physically present.
Model 600 mode says Cool1, but the
compressor does not engage
Verify the connection to HVAC unit. Ensure the short-cycle
timer is not inhibiting the unit.
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