What is a Volt Free Contact?
A Volt Free Contact (VFC) is a simple electrical contact that allows an ATC chiller to provide an alarm or status signal to external equipment.
It is called “volt free” because the contact itself does not supply a voltage. Instead, it acts as an isolated switch, allowing the customer’s own control circuit to detect a change in the chiller’s status.
Volt Free Contacts are standard on many current ATC chillers, making them a straightforward way to integrate chiller status into a wider process or controlled system.
How does a Volt Free Contact work?
The VFC operates like a switch within an external electrical circuit.
The customer provides the control voltage for their circuit, while the chiller changes the state of the contact according to its operating or alarm status.
On applicable ATC chillers, the contact opens when the chiller enters an alarm condition.
The customer’s external equipment can detect this change and respond accordingly.
Because the contact is electrically isolated, the chiller does not need to provide the operating voltage for the customer’s monitoring circuit.
What can I connect a VFC to?
A Volt Free Contact can be connected to compatible external monitoring or control equipment, such as a:
- PLC
- Building Management System (BMS)
- Machine control system
- Test system
- External alarm or monitoring circuit
The exact integration will depend on the customer’s equipment and control system.
Always refer to the model-specific product manual for connection and electrical information before wiring the VFC.
Why are Volt Free Contacts useful?
Many process cooling applications form part of a larger machine, test system, or production process.
A VFC allows that wider system to recognise when the chiller has entered an alarm condition without requiring an operator to continually monitor the chiller itself.
Depending on how the customer’s control system is designed, the signal could be used to alert an operator or trigger an appropriate response elsewhere in the process.
This can be particularly useful where the chiller is:
- Integrated into OEM equipment
- Supporting an automated process
- Installed away from the main operator
- Part of laboratory or test equipment
- Providing cooling to a process where an alarm needs to be recognised by a wider control system
Is a Volt Free Contact the same as RS485
Volt Free Contacts and RS485 provide different types of communication.
A VFC provides a simple change of contact state that external equipment can monitor. It is useful when the customer primarily needs an alarm/status indication.
RS485 provides digital communication with the chiller controller and can be used to read or write controller information, including remote adjustment of the temperature setpoint.
On current MG, G, and H series chillers, RS485 and Volt Free Contacts are both provided as standard.
Can a Volt Free Contact remotely start or stop my chiller?
The standard Volt Free Contact is intended to provide an alarm/signal status to external equipment; it is not the Remote Stop/Start function.
Where remote control of the chiller’s operation is required, ATC offers a separate Remote Stop/Start Option Pack (OP00005) on compatible models.
The Remote Stop/Start function requires a customer-provided +24V signal through the appropriate connection.
Similarly, standard RS485 communication should not be assumed to provide remote stop/start functionality.
How do I connect the VFC on my chiller?
On current MG, G, and H series chillers, RS485 and Volt Free Contacts are provided through a 9-pin D-sub connection.
The customer supplies the control voltage used by the VFC circuit.
Always refer to the manual supplied with your specific chiller for the correct pin-out, electrical requirements, and connection instructions before integrating the chiller with external equipment.
If you’re unsure how the VFC should be incorporated into your system, contact ATC.
