Hissing sound when A/C is on
 

Hello everyone I have a problem with my 2000 Expedition 4x4 XLT. When I have the A/C on theres this hissing sound comming from the rear, I think on the drivers side. Any ideas?
Also my truck have rear air.
Thanks ~Gage~

Usually a hissing sound would be a vacuum leak, but I know of no vacuum lines going to the rear unless there is a line in the console.

Maybe the rear blend door is stuck. Just a thought.

Thanks for the info, weird thing is that it only makes that hissing noise when in A/C mode.
I didnt know there was a blend door in the rear.
~Gage~

From what I've read the rear blend door uses an electric motor instead of vacuum as in the front.

You're hearing refrigerant flow through the orifice at the rear evaporator core. It echoes through the overhead ductwork, and is rythmic with the cycling of the compressor. You'll hear the same "hissing" noise from every '97-'03 Expy/Navi with rear A/C. It's more pronounced when the vehicle is a bit low on refrigerant.
JL

There are two blend doors in the rear, both are electirc. They are on the p/s not the driver side. Typically what breaks is the gear on the blend door actuator, not the door itself. When they break you get a clicking / thumping noise, not a hiss. In the front the axle on the door tends to break.

I have the same problem in my '03..but I think mine is due to a leak somewhere. I've shot it with refridgerant and still have the hissing sound that is only coming from the rear. The shot only lasts a day at most..any ideas? It's getting steamy here in Virginia Beach and having a Black Expo with black leather seats isn't any fun with no a/c

So I still having problems with my A/C when its on its not cold at all front and rear. Does this sound like it needs to be recharged? So I bring it to the dealer?
Thanks ~Gage~

i have the same exact problem with my 2000 expy 4.6
i will recharge my a/c system this weekend. i will keep you updated.

I was going to try this stuff, what do you think? IDQ - Auto A/C Products & Sealing Solutions

It may work if the leak is coming from a loose hose crimp or o ring, but most A/C leaks come from the compressor shaft front seal, and the comp needs to be replaced, if you dont have the tools to change just the comp seal, and changing the comp seal is a hard job, its better to just r&r the entire comp and clutch assy. look for oil around the front of the a/c comp clutch area, anywhere you find oil at on a/c parts, you will have a a/c leak, dish soap and water in a spray bottle will help to find a/c leaks, fords love to leak freon at the evaporator area, inside the cab.

the a/c service ports have a shrader valve in them, and love to leak, when removing the caps, if the valve area is wet with oil, replace the shrader valves, hope that helps, Chellie

Hi :) JL is right, if you are not loosing freon, and your ac is cold, your hearing the liquid freon being sprayed into the evaporator tube inside the evaporator, thats what causes the evaporator to get cold, liquid changing into a gas, three devices cause the freon to get cold, #1. orfice #2. expansion valve #3 capillary tube, all 3 cause a liquid freon to change to a gas inside a evaporator to cause it to get cold. hope that helps, Chellie

Thanks for the info CHELLIE, my A/C hasn't worked in a few years it just blows warm air front and rear so I hoping that all it needs is a recharge.
~Gage~