Hissing noise, heat only blows out vents...

Welp before I left this morning I started my wagon up, but only a few moments after there is a hissing noise from inside somewhere...

I also tried to turn my defroster on and it did blow, but only out the vents.

Anyone have any ideas?

Thanks in advanced as always!

My wagon makes a hissing noise in floor or off positions only. I'm wondering if either a vacuum hose came off under the dash or one of the piston seals failed.

My hissing is from when I turn it on until I turn it off...

I tried looking under the dash with no luck, I'm assuming I have to take the whole dash apart?

You can't locate the hissing noise? Use a 3-foot length of clear 3/8" tubing from a hardware store as a directional microphone - stick one end in your ear, then poke around under the dash with the other end. I've used that to pinpoint noise sources.

Boomhauers_93Wagon wrote:

My hissing is from when I turn it on until I turn it off...

I tried looking under the dash with no luck, I'm assuming I have to take the whole dash apart?

You have a vacuum leak somewhere. A hose could have popped off, but more likely than not, one or more of the vacuum hoses has finally degraded and is now leaking. There's also a vacuum reserve tank under there somewhere.

Going from memory...you have to take the dash trim off. That's probably the easiest part. A few screws, careful removal (as the assembly is fragile) and you're free. To get at the climate control head requires removing the ashtray and cup holder (four screws, wiring harness). Actually removing the climate control head requires that you first disconnect the linkage operating the cold/hot blend door. GM says that if you don't, you will break the cable off at the blend door.

There is a repair for this mentioned in the service manual if it does happen, but it sounds tedious and probably requires taking even more stuff apart...so I'd highly recommend not breaking it. You're supposed to be able to press in a retaining clip to let the control cable come loose (you can see it from underneath). I ended up breaking the retaining clip, but that seems far less serious, as the cable is held in place by other means and isn't too "inclined" to move around.

Then you can remove the climate control head and inspect those vacuum lines. There are two sets...one large set that governs all of the main climate control air directing operations and another, smaller set that controls the recirculation mode. The vacuum reserve tank is supposedly somewhere around the A/C evaporator (not sure if you have to remove it--but I hope not!). At the end of the vacuum lines furthest from the climate control head, you will find a plastic block that all of them run to.

My wagon has a vacuum leak somewhere in the dash. While the controls still work fine, I can hear the leak and vacuum loss when I shut the key off. I haven't looked into this yet.