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I Recently did a a/c job on my 2009 F-150, I replace the evaporator core and the expansion valve, I did a vacuum decay test before charging and it hold @30in of vacuum for over a hour. I went and charge the system with 24oz of Freon as per spec. Everything look good but know I can hear a HISSING NOISE FROM THE HVAC DUCT, it looks like is coming from the expansion valve. I put my ear next to the evaperater box and you can hear the hissing sound all the time, it sounds like the gas interning the evaperater core. But every 30 or 45 sec its get a little louder enough where you can hear it from the cab, it last about 3-5 sec then its goes away. I think it might be the expansion valve, or maybey the after market evaporater its louder . Don't really know right now. I bought all the parts from out local auto parts. Everything work fine, temp drops down to mid 40 .What do you think?
I'm sad to say I've had a couple vehicle where if you use aftermarket evaporator you can get noise. I always go OE if the part is that far in to replace. ☹️ Only other cause I've had is a low charge which I'd assume you don't have.
I have experienced the same kind of "hissing" noise, especially with Fords. This hissing noise is normal. It is caused by the pressures in the system equalizing. Anytime the clutch on the compressor shuts off or the engine is turned off, after the a/c has been operated, the high side will bleed down to the low side until the pressures equalize. This noise is fine. My guess is that due to the usage of aftermarket parts, it may be a little more noticeable!
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