Why is the A/C temps rising


Well-Known Member
Thread starter #1
I just had a special run ti Idaho Falls. Normally I am out and back home daily. When driving the wife was microwaving some potato's for dinner and all of a sudden the a/c started blowing warmer. I keep a temp prob in the vent cuz I like to see what the temp is coming out. The temp is normally 42* it rose up to 60*. I clicked over to volts on dash and it dropped to 12.5v. I was running 1300 rpm then dropped down a gear ran it up to 1600 rpm and volts went back to 13.9v and the temps went back to 40ish. I will be putting in an amp gauge this weekend to actually see what is going on. Just wondering why the a/c temp would climb like that is it controlled by ecm and lowered it because of voltage drop? Normally only run the micro for a min or 2 to warm lunch so this doesn't really matter, just wondering WTH.


curmudgeon extraordinare
I'd have to go measure all the pulleys, but your a/c compressor just isn't turning fast enough at 1300 rpm.

While the lower rpm is great for economy, it's not so great for system efficiency like the AC and alternator.


Friendly Neighborhood Former Technician
Staff member
Yes guess I left that part out. 2016 Cascadia. That sounds like what it is. Like I said that shouldn't be a problem micro doesn't usually run more than a min or two.
True enough but it’s not about voltage you see on the gauge it’s about voltage at the sam_cab pin. Which could have a little resistance compared to what you see on the dash. And sometimes they hiccup and when the voltage pulls down it will leave that stuff off until you cycle the key. But it’s not uncommon for my 700 watt microwave with the truck at idle to pull it down to 12.5 get a little age on the batteries and it will dip a little lower.


Instigateur №166™
I wouldn't think 12.5 was low enough to cause problems, but it sounds like the lower voltage caused the blend door to move. A small drop in fan speed shouldn't have effected temp that much.


Well-Known Member
So basically don't nuke potatoes if you want cold AC. Your alternator can't keep up at cruising RPM.

Sounds normal, TBH. No different than charging your battery faster after a jumpstart by revving the engine.