How Can We Help?
Print

How do I wire a PEARL to control a variable speed fan?

Note:

There is a detailed diagram for this installation in the PEARL’s installation guide.

Type of signal:

The PEARL can adjust a supply fan speed of an HVAC unit based on the active cycle the HVAC unit is in. The type of output from the PEARL is a modulating type; 0-10VDC. The VDC output is proportional to the desired fan speed. For example, if the PEARL outputs 2VDC, then the fan would be at 20% fan speed.

Wiring the PEARL to a Supply Fan Variable Frequency Drive (VFD):

There are a variety of different VFD manufacturers that have their own representative terminals that get wired to. For further assistance outside of this article. contact Pelican Technical Support.

When wiring a supply fan variable frequency drive to a PEARL, you will us the (A2) output from the PEARL to control the fan speed. 

  1. Use a standard 18G unshielded thermostat wire and wire the (A2) output from the PEARL to the 0-10VDC speed input at the variable frequency drive (VFD). 
  2. Use a second 18G unshielded thermostat wire and connect the common (C) terminal from the PEARL to the variable frequency drive’s speed input common (-) terminal.
  3. All variable frequency drives have a start/stop input. This is normally a 24VDC signal. Because the PEARL only outputs 24VAC, you will need to install a 24VAC normally-open relay at the VFD. Use a third 18G unshielded thermostat wire and connect the (G) terminal at the PEARL to one side of the relay’s 24VAC coil. Use a fourth 18G unshielded thermostat wire and connect the common (C) terminal at the PEARL to the other side of the relay’s 24VAC coil. Find the 24VDC power source at your variable frequency drive. Wire a new 18G unshielded thermostat wire from the 24VDC power source to one side of your normally-open relay’s contact pin. Find the 24VDC start/stop input terminal at your variable frequency drive. Wire a new 18G unshielded thermostat wire from the other side of your normally-open relay’s contact pin to the start/stop input terminal at the variable frequency drive. 

When wired correctly, when the PEARL wants to enable the supply fan the follow will occur:

  • The PEARL’s (G) output will enable, placing 24VAC onto the normally-open start/stop relay’s coil, closing the relay’s contact. When the relay is closed, 24VDC will be made to the 24VDC start/stop input at the variable frequency drive. This should place the variable frequency drive into RUN mode and the supply fan should run at a minimum at the variable frequency drive’s configured minimum fan speed.
  • The PEARL’s (A2) output will send a DC voltage to the 0-10VDC speed input of the variable frequency drive. The variable frequency drive should run the supply fan based on the voltage output of the PEARL. For example, if the PEARL outputs 8VDC, the supply fan should be at 80% speed.
If the above sequence does not occur, contact Pelican Technical Support for further assitance.

Example Diagram

Below is an example diagram for wiring a variable frequency drive to a Pelican PEARL. Note that this diagram only represents the required connections from the PEARL to the variable frequency drive. Many frequency drives require additional jumpers to be installed and dip switches to be set correctly at the drive. Please reference the variable frequency drive’s manufacturer’s installation documentation for more detail OR contact Pelican Technical Support for further assistance.