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Hello - new to the forum - bought an '11 F350KR 6.7L DRW a week ago (23Kmi) - with a/c on i hear a hissing noise periodically...is that normal? - it kind of sounds like something actuating - is that the a/c compressor going on/off?
listen down by the passenger side. it may be a vacuum hose off or broken,...(down by heater). another neat way is to get some 1/4" or 1/8" hose or tubeing, 3ft or so long, hold one end @ your ear, then move the other end around where you think the sound is coming from....J
Turn up the radio! Seriously it might be the blend door actuator(s). Do you have single or dual zone heat/AC controls?
Turn the key forward to power everything up but not turning the engine over. Turn down the fan speed or off completely. Actuate the temp control and see if that’s the noise you hear? If it’s erratic you may not need to work the hot cold **** as it will actuate or flutter on its own if you do have a bad actuator. When they go bad another symptom is you can’t maintain temperature either with cold or heat.
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