Be careful any time you are trying to lay across the engine compartment...
I was doing that when the plastic "T" connector that goes to the heater core had to be replaced.
It never occurred to me, that the purge valve and other things sit under the pretty Vortec engine cover.
When it came time to replace the purge valve, I saw where it was and realized... Dang! I am glad I didn't snap that thing off when I was sprawled across the top of the engine working on the heater fitting!
I made a mental note to be more careful when trying to reach things at the back or deep down below.