Sites abound describing types of heaters and coolers and how each work, yet I cannot easily finding the answer to what should be a very very simple question:

For a roof packaged Gas/Electric A/C unit here in central CA (temps don't get below 32 very often) is Freon used for heating?

I've read heat pumps with low freon can ice up and then shutdown the condenser so the symptom is intermittent blow of hot/cold air yet running continuously. This is the symptom I'm having at the moment and there was a low freon condition earlier this year that was recharged. However, I'm hoping the answer will be Gas only heating units work differently and the problem is "likely" something else.

I would provide you with the model/SN off my American Standard 2.5 unit but the placard is external and the sun has baked it off completely. I couldn't even get an impression using paper and pencil shading. A quote to replace my 2.5t unit with a 3.5t was for 2YCC2042A1064A