Why is my electronic expansion valve not working

Hello, I am building a model of a heat pump air conditionerI am trying to use an electronic expansion valve for throttling, but my electronic expansion valve seems to be in a fully open state all the time, and there is no expected throttling effect, what is the reason? Below is a diagram of my model. T1 and T2 are the temperatures across the evaporator to measure the superheat, and constant 5 is my target superheat.

[Yifeng Tang]

Suggestion: set up a test harness model first.

Use a reservoir, at high pressure and some subcooling, as inlet to the valve; use another reservoir, at low pressure and some superheat, as outlet of the evaporator. Test your valve and algorithm in that model first.

Then make the inlet reservoir a controlled reservoir, vary pressure, maybe also subcooling, as a function of time, see if your expansion valve is able to maintain a superheat.

A smaller model may also help the community look at your model, if you'd like to share.