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2010 Focus A/C hiss in dash and does not cool the air

Car is approaching 100,000 miles. While driving today I noticed a rhythmic hiss coming from the dash when the AC ran. No temperature difference between AC and vent after a little while. Is there anything I can look for before I take it into the shop? I will take it in and have them put die in to find potential leak before we start with the more expensive repairs, but would like to save where I can.


I searched Ford Technical Service Bulletins to see if there’s a common problem, but no luck. I don’t want to just guess and lead you astray.

Sorry I can’t help much, but I’ll bump you up to the top, again. Somebody should weigh in here.

By the way, you’ve done a good job identifying the car and the specifics of the problem!

Well if I had to guess the blend doors are vacuum activated, so I might look for a disconnected or broken vacuum line. If vacuum lines do not control the blend doors my apology in advance.

I agree with Barkydog; sounds like a vacuum leak. I do not have the Helm electrical/vacuum manual so I can’t pinpoint the problem for you.

The hissing sound is from refrigerant gas passing through the expansion valve. There should be liquid refrigerant passing through the expansion valve, not gas, the system is nearly empty. Look for oil stains on the compressor, condenser and plumbing. Where there is a refrigerant leak there is usually refrigerant oil leaking also. You will likely need to have this diagnosed and repaired by a professional.