When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
With the defrost on, the fan at '1', lowest, and stopped at a light or at idle, when the A/C cycles on, there's a 'puff' or kind-of a 'breath' the blower seems to take. Is this normal?
I can't hear it if the blower is on 2 or higher and when driving since the fan noise/road noise covers it up.
I don't own one, I work on them.... If your def is on, your compressor will be cycling on/off. When it goes off, the 2 unequal pressures in your AC system will try to equalize thus causing a hissing sound through the orifice tube. Don't take my word for it though, take it to the dealer.
It could also be your compressor lowering the idle thus taking more voltage from the system as it locks up(until the idle picks back up). This could cause a slight change in fan speed and could be interpretted as a breath like sound.
Thank you for your input. I don't notice any change in the RPM--I did try to watch for that. I'm just surprised to see/hear this much with such a large motor. I came from a 2.4 liter inline 5 and with that one, the RPM changed when the A/C cycled, but there were no other noises, etc.
Where is the orafice tube located, anyhow? Is it close to the cab? I did stop at a dealer several weeks ago and asked about it. The service tech felt it was normal as well, and he owns one!!
The orifice tube is inside the A/C high pressure line near where the line goes into the firewall/evaporator. You can't see it without disconnecting the line(you have to recover the refrigerant first and vacuum the system though to disconnect lines).