What is this?

[quatin]

I'm replacing the valve cover gaskets and noticed this hose. Being a 21 year old car, I try to replace hoses whenever I can, this one feels rock hard. Part of the HVAC system?

Shared album - Jay Zee - Google Photos

 

[alumarine]

It's an air conditioning hose.
No need to replace unless it's leaking.

 

[HiLife]

Yup, low pressure ac hose.

 

[02_SE_Runner_DAD]

AC hose, probably want pro to do it but no need to replace if it doesn't leak.