Question The mechanics at work say the temperature coming from the air vents only needs to be 15 degrees lower than ambient temperature (outside air temperature). I need proof to show the shop supervisor this is wrong. When it is 90 degrees outside, 75 degree vent air isn't cold enough.
Please help if you can - thanks!
Answer Hi Dave,
15 degree difference? Bah. That couldn't be more wrong. These guys are actual mechanics? All kidding aside, even poorly designed r-134a vehicles can maintain at least a 25 degree difference on a 100 degree 100% humidity day (the *hardest* day for an A/C system). Most cars can maintain a center outlet temperature in the low 40's on a 90 degree day, even in moderate humidity.
Take a look at this, it's from Mobile Air Conditioning Society. It's a little bit more than you need, but it's THE reference for MVAC. The figures in this document are more concerned with pressure relationships, but they also list the outlet temperature and ambient temperature -- which is the 2 things you're most concerned with. The average difference you see, based on those charts, is 35-45 degrees.
Now, I can't post a Temperature chart here for copyright purposes, and most all of the manufacturers charts are on their own sites, and you either can't access them, or you have to pay (even www.alldatadiy.com). However, this should prove your point. If it's not enough, then visit your local Volvo dealer, and I'm sure they could print out a A/C Performance Chart for you at no cost (if you're a customer!). Even independent shops will do this for you, since most have access to AllData or Mitchell.
You are absolutely correct in this instance. Good luck!
