It probably doesn't have an expansion valve but it might. I was just saying that there could be other problems. It is probably an orifice or capillary tube system.

If you can find an expansion valve it should sense heat with a tube going to a bulb on the low side line leaving the evaporator. An expansion valve regulates heat in the low side line by releasing refrigerant into the evaporator. You could try to chill the bulb and heat the bulb to see if anything changes. It would be a long shot.

Do you have a make and model number?

BTW, I'm not an AC repair person. I have the certification from self-study but I just fix my own stuff. I have to learn as I go.