Common Installation/Operation Mistakes
Ventilation Components Connected to the Wrong Relays
A common mistake is to connect the ventilation equipment to the wrong relay contacts. All
contacts are labeled as either “NO” or “NC” to designate their powered-off state. If connected
to the wrong terminal, equipment that is supposed to turn on when the setpoint is reached will
instead turn off. Similarly, equipment connected to the wrong numbered relay could activate at
undesirable setpoints and delays.
Relay Levels Set Incorrectly
Relay Level 1 is the most common level that will be used in most circumstances. However,
multi-speed fan setups often require the use of distinct relay levels. Equipment wired to the
“NC” terminal will activate once the setpoint has been exceeded or an error state has been
entered. Relay Levels 2-4 use the “NO” terminal to achieve this feat. Equipment wired to “NC”
at these relay levels will always be active during normal operation. Furthermore, higher relay
levels will disable lower relay levels when active. If ventilation components are running when
they should not be, or not running when they should be, check the relay levels and the wiring
connections at the terminal blocks.
Improper Communication Wiring
Improper communication wiring, or exceeding the number of nodes on a single bus, can cause
communication between the panel and transmitters to be inconsistent. The GDCP-Touch uses
Modbus RTU over RS-485 for communication. All standard guidelines apply for this type of
wiring. Ensure that a shielded, twisted pair cable is being used and that the cable is free from
interference. Cable lengths under 500 feet may use either a daisy chain or a star
configuration. Anything longer must be a straight daisy chain and a 120 Ω termination resistor
must be included at the farthest transmitter in the chain. If too many sensors are connected on
one bus line (e.g., 32 sensors connected to the control panel without any expansion packs),
communication between devices may be erratic. Be sure to include GDCP-ExpansionPacks
where necessary to repeat the original signal and create a new bus for more sensors. Also,
verify that the incoming communication enters the relay board at the isolated terminal block as
shown in figure 16 on page 57.
Setpoint Level Set at Wrong Concentration
A setpoint that is too low can cause frequent cycling of the ventilation system, leading to
excessive wear on components and increased cost of operation. Adjust the setpoint
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Rev 1.1 – May 18, 2021
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