Claude Sonnet 4.0 didn't say "nope" to the same prompt but also didn't agree. It replied:

Actually, 24V control signals in HVAC are typically AC, not DC. Most residential and commercial HVAC systems use 24VAC for their control circuits. This 24VAC comes from a step-down transformer that reduces the standard line voltage (120V or 240V AC) down to 24VAC. The reasons for using AC include:

* Safety - Lower voltage reduces shock hazard

* Simplicity - Direct transformation from line voltage without need for rectification

* Cost - AC transformers are inexpensive and reliable

* Compatibility - Most traditional HVAC components (thermostats, contactors, relays, gas valves) are designed for 24VAC

However, you will find 24VDC in some applications:

* Modern digital/smart thermostats and controls

* Building automation systems (BAS)

* Some newer high-efficiency equipment

* Systems that need to interface with low-voltage DC electronics

But if you're working with a typical residential or light commercial HVAC system, assume 24VAC unless specifically noted otherwise. Always verify with a multimeter set to AC voltage when troubleshooting!