Need help with WiFi thermostat - no C terminal on AC unit

Ok, weird problem. I already installed a Honeywell WiFi thermostat at my house years ago, and had to run a C wire from my AC unit to the controller. Worked no problem.

Now, I’m installing one at my parents’ house. Weird thing… There’s no C “connector” on the AC unit, though there’s a place for one. What the hell do I do? Can I connect the wire to the “common” for the 24v instead? Can I ground it to the chassis?

For the record, using the 24v common worked. I found that piece of advice on another website, and was hoping to confirm here. As it was, I was very tired and really wanted to get home, so I tried it and it worked.

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The C wire is the common off the air handler transformer. In the future I would use the Honeywell prestige IAQ thermostat. Only need 2 wires to the the thermostat. There is a equipment integration module (EIM) that you install near the equipment that it remotely speaks to. Works a lot like the the Wi-Fi model but with more functionality and can be had for about the same price. I use them to integrate humidification control, condensation pan sensors, UV light control, etc