Help with a leak - 99 Exp 4.6L 4WD

[pourty]

I've recently replaced my radiator and flushed out the system (intercepted the heater hose with a garden hose and flushed it while running and heat on high). After I did that, I wondered how to get all the tap water out of the system. Basically I've just filled it up with distilled water a few times, let it run for 30 minutes with the heat on high, drain & repeat. I figure if nothing else, that will dilute it enough to not worry about it.

Anyhow, I haven't put actual coolant back in it yet, because I suspect I have a leak in the coolant system. Everytime I turn it off, I hear a hissing sound for about 30-45 seconds after the engine shuts down. I followed my ears but couldn't find the source. My only indication is that this cannister (see photo) had water all over it after I shut it off yesterday. It's either condensation or water from a leak, I can't figure out which. I have NOT run the air conditioner at all, just idling with the heat blasting.

Anyone give me a pointer as to what this part (in the photo) is? Could this be the source of the leak? I really don't want to fill it with coolant and find out I have to redo this all over again, rather waste more water...

 

[pourty]

One other detail, not sure if this is related, but sometimes the heat vents in the rear of the vehicle only put out cold air, it seems rather intermittent, not sure what would cause this?

 

[toms89]

Looks like your pointing at the front a/c accumulator.

Do you have defrost on? This will turn on a/c compressor.

Also if the a/c compressor has been running you may hear the pressure equalize in the lines after you first shutdown.

 

[pourty]

OK. I'm thinking there may not be a leak at this point. I filled it up with coolant and went for a 30 minute drive, then parked in the driveway with a sheet of cardboard underneath. Not even a drip after nearly an hour.

Thanks for the answer!