I originally posted asking what you see in the pictures due to me being 5 hours away from the person who needs some service. The responses were that it was an anti sweat mixing valve with an elbow which then later I got better photos to see that.
I've faild at attaching a link to a diagram of what is most likely inside but this is probably not the same brand. I assume it's similar with the check valves, springs and o-rings. The diagram is on home Depot website for" Legend 1/2" anti-sweat valve" under additional resources. I tried attaching the link to the PDF as well as just the link to the product and I can't figure out what you need to do because it's failing with an error message.
She says currently the water from the sink cold water supply and the toilet water feel the same temperature. I understand these can be service but my question is if it's never been opened will the rubber pieces be an issue. Could be 15 or 20 years old.