Found problem, but have question and pics. 6th post on second page.



I have a 2004 5.4 with 65k on the clock. I have noticed that when I turn off the engine there is a hissing noise coming from the pass. side (area in pic). It goes for about 30 sec and quits. I am 99% sure it is a pressurized gas escaping form a small leak somewhere, but I can't find it. I also think this hissing is happening while the engine is running, but I can't tell because of engine noise. Is this hissing normal? If not, has anyone had/heard of this before to give me a pointer on where to look/what to do about it?

 

A/C related?

 

mine does it..ac on or off. ive heard a couple others do it too so if its not normal, then at least its not just mine.

 

A/C works fine if that's what you mean.

 

Sounds like you've been running the AC or defrost. Mine does it too.

 

Vacuum canister leaking down maybe..

 

I run defrost 90% of the time i drive lol.

What does that mean. Is it supposed to happen?

 

mine doesn't but I have a 99. Theres a vacuum canister that reserves vacuum to operate the 4 wheel drive and the HVAC vents. might be its leaking or who knows maybe on the 04+ its supposed to do that i dunno.. I do know its located by the battery on my truck.

 

Pressure in the AC lines equalizing the high side to low side. Next time you go out set the HVAC to the panel mode, no ac. If the noise goes away that is what was it.

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The noise happens when I have ac off and defrost on.

 

The A/C Compressor runs when the defrost is turned on. It is designed that way to remove humidity from the air

 

Ok, I'll drive home with ac and defrost off and report back!

 

The only positions of the switch that do NOT run the compressor are PANEL, FLOOR, and OFF.

 

So I have been using the floor and panel instead of defrost or ac and no more hissing. Thanks guys for all the help.

 

Gett'n any riding in with this good weather we finally are seeing in what.. mid june?