You can use a VAC, or a VSIN. The VAC is only for AC Analysis whereas the VSIN has SINE source parameters and an AC parameter for the AC magnitude, usually set to 1, so that you can use the same source for AC, or Transient analysis. A VAC will be "inactive" for Transient analysis.
You can use a VAC, or a VSIN. The VAC is only for AC Analysis whereas the VSIN has SINE source parameters and an AC parameter for the AC magnitude, usually set to 1, so that you can use the same source for AC, or Transient analysis. A VAC will be "inactive" for Transient analysis.