I have no heat . return line is cold from h.core.
on 2000 Pontiac Firebird

there are no visible leaks.

Asked by for the 2000 Pontiac Firebird
Have the heater core itself flushed out! This needs to be done by a shop that knows how!! Air pressure + water.
thanks will give it a go
We have good luck with this at the shop! Check out youtube, enter your question on the search bar, you may be able to do something, if that dont work take it to the shop.