Now for the test. I followed the "24 - Heating and Air Conditioning/Diagnosis and Testing" section of the service manual that was posted here as closely as I could. I checked my ambient "feels like" temperature, the truck's coolant temp, and used meat thermometers that I just bought down here at the Walmarts. One thing I noticed the instructions say, that I didn't see echoed here on the forum, is that the engine is supposed to be revving at 1,000 RPMs. I kept that the best I could, within a hundred or two the entire time. The only thing I couldn't do that the instructions say is to check the evaporator temperature, as it needs to be over 55 degrees before beginning the test. I had just driven my truck, so I let it sit in the sun with the windows up for a half hour, until the inside temp read 100 degrees on the thermometers, so I'm sure it was within spec. Here's the ambient temp data when I let the truck sit at 4:24pm, a little over a half hour before I started. The "feels like" temp was 101 degrees, Sirius XM said 88, and the truck thought it was 98. I checked again at 5:07 when running the test, and the numbers were identical from the weather app on my phone (The Weather Channel). I will also note, I have the Panoramic sunroof, and I left the sunshade open all the way, with the sunroof itself completely closed.
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These are the instructions. The summary at the beginning is very interesting and definitely does a good job of setting expectations for the performance of the system, and also explains the role that humidity plays in the performance of the system, even noting that "an owner may expect too much from their A/C system on humid days". One thing I noticed that wasn't specified in the evaluation: time. There's no mention of how quickly the system is expected to reach temperature, which I think is left out due to the inability to accurately measure humidity and ambient air temperature in an area so localized (where the truck
actually is).
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Initially, I started the truck, and put the hvac unit on MAX A/C, per the directions in the service manual text. Very quickly, the vent temps, which started at 100 degrees, moved down to below 90 within seconds, then 80 after a minute, and kept falling. After six minutes sitting in the vents all read right around 60 degrees. I only had three thermometers, so I placed them in the drivers left and center vents, and the passenger center vent.
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After 15 minutes, all three vents were well below 60 degrees, with the passenger center being a little lower, almost at 50.
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This theme continued for another ten minutes, when I decided that's as cold as it's gonna get. I was curios if the thermometers were reading the same, so I swapped them in the vents and also tested two in the same vent. They were withing a degree of each other.
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I was also curious if the screen being on would affect the drivers side vents any, so I turned it off completely (I was listening to music and had the home screen set to XM Weather and the Climate Control screen). The temps did drop a bit, but they also didn't rise up again after turning the screen back on, so I assume they just hadn't reached rock bottom yet. After a half hour of sitting in the truck, I figured I was well within spec, even though the air from the vents never "felt" ice cold when I put my hand in front of it, the truck was cool and comfortable, and the numbers were making sense.
So, at least for my truck, following the procedure as closely as possible, with a warm engine, revving at 1,000 RPM, A/C on Max A/C setting, windows up, sunroof closed, starting with 100 degree cabin temperature, and using three thermometers that all read within a degree of each other, I am confident that the A/C in my truck is working as designed. Did it freeze me out of the truck on a 98 degree day with 60% humidity? No. But it's also not supposed to, as it's operating near the extremes of it's design intent.