heard someone say that - I will be putting vintage air (under dash) in the next few weeks, should I wait till then as I may have to change the box or the heater and air might be on the new system??
If your putting in a vintage air system all of the original heater core, box and controls come out of the car. I have done a few and they do work great.
in the meantime , just cut the hose , close it off from the heter core...so no water goes thru it...you can put an inline shutoff valve on it...but since you intend to replace , you can just cut the hose , put a bolt os so in the hose , clamp it shut .