2012 Yukon/HVAC drain sound from back?

[ABN45]

So had my heat on for the first time in my 2012 Yukon XL 5.3. After bout 15 minutes I pull into work, shut off the engine and I'm relaxing for abit and I can hear a draining sound from the back. Not really loud but enuf to hear it.

Is that normal? Went on for bout 5-7 minutes.

My 2015 Silverado doesn't do that. My first experience with this kind of GMC HVAC system.

 

[mikez71]

Weird, did it sound like it was pouring or dripping?

Rear HVAC is at the rear passenger side.
Coolant always flows to the heater core, heat on or off.
Was your AC on as well?

 

[ABN45]

Weird, did it sound like it was pouring or dripping?

Rear HVAC is at the rear passenger side.
Coolant always flows to the heater core, heat on or off.
Was your AC on as well?

If I could describe it, like when a bathtub drains.
And the air was on as I would trying to find a good in-between spot. So it went between hot and cool at times. And again it was in the rear.

 

[petethepug]

You’ll see the condensation drain behind the rear pass side wheel if you want to verify after you get out of the truck. Mine usually unloads at least a cup from the front & back on the ground when the humidity is high.

 

[mikez71]

Thinking it maybe the rear expansion valve you maybe hearing? Because 5 minutes is a lot if draining if it was fluid...

Maybe try no AC and see if it still makes noise..

Or some gas trickling back to gas tank through a bad check valve? IDK..