How's it going? I have a '97 Expedition 4x4 4.6. Everything's been working perfectly since the day that I got it. Now all of a sudden my AC isn't blowing cold air and this loud hissing noise is coming from the inside of my truck. I believe the two are related, but I don't know what the thing that is making the hissing sound is called. It only hisses when the AC is on. Also the check engine light will flash on for a second a few times while on the road and the truck begins to hesitate. If you open the back of the truck, there is a panel on the left. Once you get it open, there's a few metal hoses in there and they are very very cold to the touch. If I figure out what this is I might be able to find out what's going on by searching around this site more before bringing it in to the dealer. Thanks.

 

You have a vacuum leak. You will have to poke your nose under the dash and locate it.

 

with the hoses being cold to the touch that means the refrigerent system is working fine. do not open up those hoses. it sounds like you have a huge vacuum leak.

 

Hey thanks for the help guys. I dropped by a shop and the guy said that the rear AC evaporator (I think it was the rear, unless there is only one for the whole AC system) was leaking freon. I might take it in this weekend. Before then, I'm gonna look around here and see if I'll be able to fix it, although I doubt it. Thanks again.

Oh and I don't believe that my check engine light going on and off has anything to do with my AC problem. It might just be a coincidence. I've noticed that everytime it shifts into gear, the light will flash on and off and the engine will stumble. That could be a clogged fuel filter or one of my spark plugs, I'm might check my codes tonight.

 

if the evaporator is leaking that much it would all be gone in a matter of minutes. i think you need a new shop to fix it. it sounds like a very serious vacuum leak. that would also explain the stumble and why the engine light pops on and off.

 

You might have kicked loose a vacuum line under the dash on your truck. Our company had a '99 F-350 that had vacuum lines that ran across the passenger foot-well, and got kicked loose. The dealer wanted $300 to fix it. I had it fixed in about 30 minutes of looking.

 

Alright, my dad took it to a shop and wanted to change the whole A/C assembly for $600. He asked them if they were sure that was the problem and they didnt give a straight answer. They decided to try some sort of "no leak" liquid or freon that would seal any leaks for $150 and see if it would work. The A/C is very cold now, and the hissing sound coming from the rear evaporator is gone. I'm not sure if this fixed it or if it's just a temporary fix until the freon is all gone. I'm thinking probably the latter.

The engine stumbling is still a problem. I was actually driving on the freeway at 65 on a curve and all of a sudden my engine died. It was a bit scary, I couldn't move my steering wheel, I turned my hazzards on and tried to get on the side. I started the engine again and everything seemed fine and went on to work slowly. I'm not sure if this is related to the leak, I'm going to post some this on the 4.6 Engine board. I'm definately checking my codes tonight. It's just frustrating because my truck has been perfect before all of this. I'll keep u updated.

 

damn 150.00. for 9.00 you could have done that yourself. when was the last time you changed the fuel filter?

 

Oh man. Oh well. Such is life. Let's see, I bought a new one at the start of the year. One from Autozone. I'm going to grab a Motorcraft one this weekend...

 

Update: Alright I went to Autozone and bought a set of Motorcraft Plugs and got my codes scanned. No codes at all. When I got home, I cleaned the MAF sensor and the stumbling went away, everything's fine now. Amazing how one sensor can make my truck ride so horrible and even make my engine die on the freeway. Since then I've changed my plugs and will buy a new motorcraft fuel filter and pcv valve from Ford on Monday. Thankfully all this is over.

Since they "sealed" the leak on Friday, my A/C is still bolwing cold and no hissing anywhere. Hopefully it stays this way. Thanks for all your help.