HVAC vent temp not matching setting - is this normal?

[rocsteady]

My experience has been when I think I have the HVAC system off, A/C button not engaged, the truck will continue to blow air that is far too cold to be simply air vented in from the outside. My fiance and I agree that it is either going to make us too hot or too cold and the line between the two is very fine; moving the temp reading up or down a degree will make it change. Long way of saying we find it difficult to maintain a steady, cool/comfortable temp inside the cabin when it's particularly warm out.

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[moose33]

Electronic Windshield Anti-Fogging Sensor (EWAFS). Even if you turn the AC off, the computer can override your command.

 

[Jason B]

The AC in your vehicle is not like the AC in your house. The climate control will regulate both hot and cold air, at the same time, to get the truck to the desired temperature. Hence, the blend door in the system. When I get in my truck and it's 100F, the air will be ice cold. Once it get to set point (72F) the air isn't so cold.
Note that this is on those with Electronic Climate Control. It doesn't work that way on those with manual climate control, such as XL and STX.

 

[bigb]

Still don't know what to believe sounds like some are saying that, even when not in AUTO mode the temperature of the air vents still fluctuates to hit the temp setpoint?

That is what I am saying, I an never in AUTO since when I change the fan speed it kicks it out of AUTO. I'm going to put one of my AC duct thermometers in the vent and start watching it, although I am able to feel the temperature differences easily so I know it's happening, I just don't know how much it changes in numbers.

 

[alrashid2]

That is what I am saying, I an never in AUTO since when I change the fan speed it kicks it out of AUTO. I'm going to put one of my AC duct thermometers in the vent and start watching it, although I am able to feel the temperature differences easily so I know it's happening, I just don't know how much it changes in numbers.

Thank you, this seems to match up with what I'm seeing in mine too so sounds like it's normal!

I stuck a meat thermometer in briefly while idling but couldn't get it to stay still while driving and haven't had a chance to test more. Report back!

 

[bigb]

Thank you, this seems to match up with what I'm seeing in mine too so sounds like it's normal!

I stuck a meat thermometer in briefly while idling but couldn't get it to stay still while driving and haven't had a chance to test more. Report back!

Well today's test observations seem to point to what others are saying, that the system is just trying to reach the setpoint. I left my house with the truck having been parked in the garage so it was about 80F, outside it was full sun and about 90F. Set to 75 or 76 the output air dropped to just over 40F while cruising steady at around 45MPH measured from the center vent.. At stop lights it would rise to about 50F but as soon as I started moving it would drop again.

When I switched to 78F the air coming out of the vents increased in temperature right away to between 55 and 60F. I reached my destination and parked in the full sun. I came out 30 min later and started back up for the drive home leaving it set on 78F and I bumped the fan speed down one and back up to kick it out of auto. The cab was warm from sitting in the sun. This time it started putting out air close to 40F again and eventually it warmed to around 50 when I was nearly home. This tells me the system is just putting out what it determines is needed to reach the chosen setpoint as quickly as possible. I'm not sure where the thermistor or thermistors are located but I suspect there is one in the ceiling near the courtesy lights.

On older systems the temperature would adjust simply by mixing warm air with the refrigerated air which was somewhat inefficient as the compressor ran full out all the time but I believe, and I hope, that these systems are smarter and are using variable compressor outputs to regulate temperature.

One thing is for sure, this truck has the best AC of any vehicle I have ever owned. My Diesel Superduty was great but this is even better.

 

[alrashid2]

Thank you for reporting back with same data, brother! Yup it seems to confirm what you and others had said. Pretty cool! And glad to know my system is working properly too. Wish the owners manual just explained this at least - it doesnt even tell you what AUTO does!

 

[Jason B]

Well today's test observations seem to point to what others are saying, that the system is just trying to reach the setpoint. I left my house with the truck having been parked in the garage so it was about 80F, outside it was full sun and about 90F. Set to 75 or 76 the output air dropped to just over 40F while cruising steady at around 45MPH measured from the center vent.. At stop lights it would rise to about 50F but as soon as I started moving it would drop again.

When I switched to 78F the air coming out of the vents increased in temperature right away to between 55 and 60F. I reached my destination and parked in the full sun. I came out 30 min later and started back up for the drive home leaving it set on 78F and I bumped the fan speed down one and back up to kick it out of auto. The cab was warm from sitting in the sun. This time it started putting out air close to 40F again and eventually it warmed to around 50 when I was nearly home. This tells me the system is just putting out what it determines is needed to reach the chosen setpoint as quickly as possible. I'm not sure where the thermistor or thermistors are located but I suspect there is one in the ceiling near the courtesy lights.

On older systems the temperature would adjust simply by mixing warm air with the refrigerated air which was somewhat inefficient as the compressor ran full out all the time but I believe, and I hope, that these systems are smarter and are using variable compressor outputs to regulate temperature.

One thing is for sure, this truck has the best AC of any vehicle I have ever owned. My Diesel Superduty was great but this is even better.

I'm not exactly sure on that part. I think the AC compressor seems to be running most of the time, even with full heat. Mainly for humidity control.
On older vehicles, I could hear and feel when the compressor engaged, but not on these trucks.

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