jallen9339

Hi all, I'm new to the forum/Jeep community (just bought a 98 XJ). I've already learned a lot from this forum, and I'm grateful for the pooled knowledge on this site.

I have a (hopefully) minor thing I've noticed, and haven't seen any other mention of it after nosing around the internet about it. I've noticed that when I do not have my air or heat running in the Jeep, I hear a small hissing sound. This is weird because most people would hear noises when your climate system is running, but I notice a slight hissing when I turn the climate control system off, even if I'm in park. As soon as I turn it to A/C, or the heat setting, the slight hiss goes away, and it's just the standard sound of the fan running, which is still quieter than when the system is off!

Just curious if anyone else has had this happen, or has heard of it happening. Maybe it's normal? I will add that my A/C is currently not working, planning to fix in the spring. Not sure why this might make a difference, but will mention it.

Thanks for any input!

exasemech

Turn the key to "run" but don't start the vehicle. You now should be able to turn on the fan etc (without the engine running) . Do you still hear the hiss when you turn the fan off after you wait a bit? If you do not, the hiss is likely a vacuum leak, probably under dash on right side somewhere.

jallen9339

Nope, I don’t hear a thing with the engine off. It very well could be a leak, it was throwing a p0171 code a few weeks ago, which can be caused by a vacuum leak. Now to track it down (looked previously for a leak with no luck). Thanks for the help!

robsjeep

Snakes.

RocketMouse

maybe someone knows if they make a kit for smoke. That would help find a vacuum leak.

exasemech

Actually a length of fuel line or vacuum line or similar works pretty well. Stick one end (carefully) in you ear and probe and listen for the hiss with the other end. Crude but it works .
Probably not OSHA approved
you are trying to locate the noise, not get your eardrum sucked out.

jallen9339

It’s near impossible to hear the hiss outside of the truck with the engine running, I can hear it best inside the cabin, it sounds like it’s coming from under my airbag panel, around the glove box

exasemech

You're getting close. Take out the glove compartment (easy 3 screws on the lower edge. You will see some colored lines and connector that sorta look like electrical stuff but they are vacuum lines . go from there
edit: found this old thread with some pics. Your leak has gotta be around there
https://www.cherokeeforum.com/f2/heater-vents-control-vacuum-pipe-configuration-85188/