My 2007 F150 Supercrew makes an annoying hissing noise about every 10 seconds that comes from inside the dash on the passenger side when the AC is running. The best way to describe the sound is like having Darth Vader riding shot gun. I've seen a number of posts for this issue, but no solutions other than turn up your radio. The previous 3 F150s I have had did not make this noise and as I understand it most do not but some do. I took it to the dealership and they said it was low on freon and charged it. This did not fix the sound. When I pointed it out do the service advisor he tried to sell me the "This is a normal sound" story which is a bunch of BS. I've got 800 miles left on my warranty and I'm not sure what to do. Has anyone solved this issue? Help.

 

Well after several iterations of working with my dealer and Ford it has come down to this from Ford. Yes we hear the noise, no they all don't do it, but we consdier it to be "normal" and we are not going to fix it. This was the verdict from the Ford Engineer. So basically I'm stuck with this defect and so are a lot of other people. Be thankful if yours does not. My previous 4 F150s did not and I'm pretty sure my next Toyota will not. Buyer beware.

 

I'm an air conditioning man when I'm not fixing up my truck. I don't do many car a/c's but I think I know what your hearing. While your driving your a/c will cycle on and off. I other words the compressor is kicking on and off regularly when the temperature you set at the t-stat is satisfied. When it cycles off your hearing the pressures in the lines equalizing. This is normal and very common. It happens many times while your driving. As far as the dealership telling you its low, sounds like bull****. You should never have to add anything assuming that you never have a leak. On an 07 I really doubt you do. There is no accurate way to tell if a car a/c is low. The pressures that they are reading are affected by the temperature outside, inside, humidity. On a cooler day your pressures may show that your low and on a warmer day it might seem like it has too much. They only way to be sure you have the right amount of "freon" is to recover it all and add the specified amount according to your label by weight. Usually ounces. Hope this clears it up a bit.

 

Mine is doing this as well I have not brought it to ford yet but am planning to it drives me crazy somtimes it is louder.

 

Sounds to me like you have condensables in the system, which is just a fancy word for either water or other type of fluid that is not freon. That fluid could be flushing agent, too much oil, or dye. The hissing sound has to inevitably be the O-tube as syarrison suggested. The O-tube could have a manufacturing defect or a simple piece of trash stuck in it. They are simple to replace and cheap insurance. My suggestion for this is a complete removal of the freon, then flush the system, replae the O-tube, then a long vacuum and a re-charge.