The Code allows conductors of AC and DC circuits rated 600V, nominal, or less, to occupy the same equipment wiring enclosure, cable, or raceway [300.3(C)(1)]. However, all conductors must have an insulation rating equal to at least the maximum circuit voltage applied to any conductor within the enclosure, cable, or raceway. If the thermostat wiring for this A/C condensing unit was run in the same raceway as the power supply conductors, which I believe it was, then we have a Code violation.
The Fine Print Note (FPN) of 300.3(C)(1) refers us to Sec. 725.136(A) for Class 2 and Class 3 circuit conductors, which does not allow you to place Class 2 and Class 3 circuit conductors in the same raceway as Class 1, electric, light and power conductors.