AC not kicking on

Hey longshot here…I’m an electrician, so you can be detailed in your response. I have a 1999 Payne model furnace. I have 2 exact models in my duplex. The front unit has no working ac, the thermostat is fine but the condenser unit outside won’t even attempt to kick on. The unit that corresponds to the non working AC is showing a steady red light in the window, while the working unit has a bright orange light. Don’t know much about residential ac. Before I attempt to change the contactor/capacitor in the condenser, can anyone tell me what the red light means? Customer service wouldn’t help me because I’m not a certified tech. Any help is appreciated, thanks.

I have an HVAC contractor that I call when mine doesn’t work.

Ditto. I pay the appropriate professional to provide the service they are trained for.

Look on the inside of the cover. The codes are usually listed right there.