Ventilation System: AC compressor 'ON' conditions

[R Black]

"I have a theory, which is mine and I have it." - Monty Python

Recently I took a road trip between Chicago and Colo Sprgs. (2020 5.3 MAX towing, otherwise 'Stripper')

It was very hot this past July.

I usually don't use the AC, preferring to run with the drivers window all the way down and the pass. rr. partially down, using a cool cushion .... truck is glacier white etc yatta. I did this despite the temps hitting 111 degrees. Don't ask, I'm not skinny but it works fine for me. I averaged about 22.5 mpg (25mpg all the way down IL river to Hanibal)
NOTE; this is with the AC OFF and the auto temp control OFF

When I got to Colorado I noticed there was reasonably cold air coming out of a lower duct (I must have had the setting set to exit there). WTH?? The AC is off, the light is off ... When I hit the AC button the car slows down ... when I turn it off the engine says 'thank you', ala any 70's GM. What the hell? why is cold-ish air coming from the dash when the compressor is disengaged? It's impossible, It's over 100 degrees out there.

Eventually I pulled over and did a compressor clutch check.
(one of the reasons I bought this car is because you can SEE the compressor, all the spark plugs etc.)

Turns out the compressor clutch is engaged, as near as I can tell, under all control conditions, except ventilation controls in absolute OFF condition (Front Climate Control Power button OFF).

My theory is the AC compressor must have some kind of dual stage pressure state, with a lower pressure activated when the system is taking it's cue from the auto temperature setting. EVEN WHEN THE AUTO BUTTON is DEACTIVATED!?! This would make it nearly impossible to have the fan on at any speed and have the compressor be completely off, that is ..... if my theory is correct. Otherwise you'd have to make a perfect guess, with the outside temp gauge also considered, and set the inside temp the same in order to prevent a 'heat on' or 'AC on' condition.

I'm fairly certain there is no malfunction except perhaps in the brains of the engineers that designed the system, who probably sat next to the guys that designed the Fuel filler necks with no dust caps.

This is not scientific but my best estimate despite dropping elevation on the return trip is ...my gas mileage increased between 1 to 1.3 mpg with the Front Climate Control Power button OFF.

Does anyone have the tech knowledge of these systems to know if there is some kind of dual stage pressure system on these compressors? The old style OEM shop manuals back in the day would state that kind of thing at the beginning of the section but I'm loathe to look at my DVD version and I'm pretty sure it wouldn't be written up there anyway.


Button

 

[LordWayback]

I believe these things have a crossover between the 2 systems (1 system but easier to explain as 2) one is like ac in the older trucks one lets you control the ac to a precise temp so even if you turn the less precise dials/fans off if climate control is on it’ll try and regulate the temperature by leaving the compressor running and letting the air kinda seep out. my dads 4 cyl Silverado (new) does the same sort of thing ultimately it’s meant to be a creature comfort. the climate control precision temp lets the ac work like a house AC where it’s ambient cab temperature and doesn’t kick off until the ambient temperature reaches the climate control set temp. the hand controls let’s you have traditional blow in your face AC. One control panel acts like your houses thermostat and the other acts like a regular car ac system I was confused when my dads wouldn’t turn off either.

 

[LordWayback]

No dual stage pressure system here one button just acts like ambient temp the other like a normal car ac that’s why it lets you chose a temp.

 

[R Black]

No dual stage pressure system here one button just acts like ambient temp the other like a normal car ac that’s why it lets you chose a temp.

So .... from what your saying it sounds like maybe if I re-did the visual compressor test with the temp set higher than outside ambient, the clutch would maybe be disengaged even though the the system was in the ON position for fan use but still with the AC button off (??)
Thing is .... I noticed that even when the compressor clutch was engaged, it definitely created MORE drag when I hit the 'AC in earnest' button.
Also all of this occured with the 'Auto temp' control button de-activated.

I dunno ...... maybe I'm wrong here, maybe I should do another, more thorough test.

 

[LordWayback]

So .... from what your saying it sounds like maybe if I re-did the visual compressor test with the temp set higher than outside ambient, the clutch would maybe be disengaged even though the the system was in the ON position for fan use but still with the AC button off (??)
Thing is .... I noticed that even when the compressor clutch was engaged, it definitely created MORE drag when I hit the 'AC in earnest' button.
Also all of this occured with the 'Auto temp' control button de-activated.

I dunno ...... maybe I'm wrong here, maybe I should do another, more thorough test.

I don’t know what you’re going for but the system basically just does it’s thing

 

[BlaineBug]

I just about always use AUTO which engages AC indicator light, however occasionally if it's cooler out or in the winter or if I open the windows, I'll tap the AC button to disengage the AC indicator light. As far as I've felt it certainly feels like the AC fully disengages, the air isn't as ice cold for sure when the AC light isn't illuminated!

I normally have inside temperature set from 72-74. I never really adjust it further than that regardless if ambient temperature is 90 or 0. No need to go to LO otherwise you'll freeze!

 

[BlaineBug]

Just the other day I noticed my A/C condensate drain was dripping on the floor of my garage. I had the HVAC turned on, but not in AUTO mode and I had also disabled the A/C by pressing the A/C button which turns off the A/C indicator light. So apparently the only way to turn off the A/C entirely is to turn off the HVAC entirely to where you have zero display and no cabin fan. Mind you only the front A/C was draining. The rear A/C unit was dry.

 

[sealandsky]

Which air distribution button did you have pressed (lit up) while you were noticing the cold air issue?

 

[B-train]

I believe all the new stuff has cabin sensors for hot/cold and humidity. It will automatically make corrections if those thresholds are met. Kind of stupid in my book.......like, I KNOW when I need defogger. Maybe I'm just trying to hone my skills and don't need something trying to save my butt if the windshield isn't perfectly clear....LOL

Or, in your case just enjoying a good sauna event. Funny thing, I did the exact same thing while cruising out west this summer from WI. But, my 2008 Denali listens to me when I say NO A/C. The hot, dry air isn't hard to handle when burning down rhe road.

 

[BlaineBug]

I believe all the new stuff has cabin sensors for hot/cold and humidity. It will automatically make corrections if those thresholds are met. Kind of stupid in my book.......like, I KNOW when I need defogger. Maybe I'm just trying to hone my skills and don't need something trying to save my butt if the windshield isn't perfectly clear....LOL

Or, in your case just enjoying a good sauna event. Funny thing, I did the exact same thing while cruising out west this summer from WI. But, my 2008 Denali listens to me when I say NO A/C. The hot, dry air isn't hard to handle when burning down rhe road.

The annoying thing is, sometimes we like to have light HVAC fan ventilation when the windows and sunroof are open - but I can clearly tell that the air emanating from the vents is TOO COLD for it to simply be outdoor ambient air. Why does the A/C button and illumination light exist if it's going to be ignored regardless?