Sam Takoy wrote:
Hi,

Am I right that (at least in the HVAC context), a relay switch is a
switch that turned on by a passing current.

For example, in the compressor, there is a line voltage cable that's
always on, but the unit does not turn on until the thermostat
completes a circuit thereby flipping the relay switch on.

Is that correct?

Yes. Similar to the solenoid on a car starter. It enables a low-voltage (and
current) relay to supply higher voltage and current to the load. Imagine the
wiring necessary to snake two 60-amp wires to a thermostat!


Also, if a contact in the thermostat is labeled "Fan Relay", does the
word "Relay" refer to the relay switch in the fan? (In that case, why
not just say "Fan"?)


Because "Fan Relay" has more letters than simply "Fan."