The vehicle is a 2005 F250 Lariat.

My first question is, when you hit the AUTO button on your auto climate control, does the AC light always light? The service writer was telling me it shouldn't, but regardless of temperature, when I hit my AUTO button, the AC immediately lights up on the control panel and will never turn off. If I want it off, I have to manually turn it off. For example, even if it 60-degrees inside & outside of the truck... if I set the Climate Control to 75 and then hit the AUTO button, my AC will activate. Is this normal?

The next question... the dealership is telling me that if you turn the climate control to AUTO and set the temperature, it will make the truck that temperature. Then if you hit the AC button (supposely to turn it ON) then the temperature will drop 10 degrees... even though AUTO is on. Is this correct? Sounds like B.S. to me. For the first 2 months I've had this truck, I hit AUTO and set the temp (so like I mentioned above the AC light has already come on) and the temp goes to the correct temperature. Now they're trying to tell me it should be blowing 10 degrees colder than you've set it. Doesn't make sense to me!

All of a sudden yesterday I started it up and saw that the EXT TEMP was reading 20+ degrees low. It took about 10 minutes for this to correct itself. But starting at that same time the Climate control wasn't behaving right. Even after the truck figured out the true outside temp (which was 80) it wouldn't cool down the cab (which I had set to 72). ... then this morning it was about 50 outside, so I set it to AUTO 72... but I had to crank it up over 80 degrees for it to heat the cab. The dealer is trying to tell me this is normal.... but it hasn't been the norm for the first 2 months I've had this truck.

 

When I hit the auto button the ac lights up. In the mornings I turn off the ac but leave it on auto. Seems to warm up faster that way. I like the climate control much better than the manual. Just set the temp and forget about it.

 

My Lexus does the same thing... and this is normal I was told.

In "auto mode" the climate control will do just that... maintain that climate. The AC runs in order to reduce moisture and will activate and remove humidity as needed based upon the temperature set.

I to turn off the A/C mode light and have not seen a difference (good or bad) that changing it really does anything except make me feel better by doing it????

Dealer is full of "hooey".

Enjoy the nice cool air and hot heat!!

Jeff

 

Iwas wondering the same thing when I first got my 05 with the auto climate. But mine does the same thing with the AC light on all the time. I just leave it, it has been working awesome. Gets plenty warm when its cold and it really cools down the cab when its hot. I like that setting the temp and forgetting it.

 

Speaking of AC.. I have not seen a MPG diff with it on or off. Anyone else?

 

My truck's auto climate does this and AC on helps the defroster work faster because of the dehumidifying of the AC.

A lot of newer vehicles will always start with the AC on and that is the reason.
You can manually turn off the AC but you will find that for comfort and quicker clearing of fog from windows, the heating system knows best. I like the climate control on my new truck. It is the first vehicle I have never had to keep adjusting heat and cold.

 

RUN RUN from your service manager, yes this is normal! The only time I have seen my A/C not lit was when it was 15 deg. outside. The system lites it but then will cycle the A/C on and off as it needs it to help with moisture and everything. Even a manual system when you turn the defrost on will run the A/C to help defog the windshield.

Doesn't make sense to me either and I've never seen that happen with my truck.

Were you moving when it took 10 minutes for the system to correct the tempature? There was a thread a few months ago that the ext temp only adjusts itself a few degrees every 30-45 seconds, or something like that, if you are sitting still. But if you are moving then it adjusts the temp reading every few seconds. That make sense since the ext temp probe is next to the radiator and can be affected by the radiator temp if you are not moving.

The system does use the ext temp does affect how the system works so if the ext temp is off you need to have it fixed or the system won't work right. In general like you have done for the last couple of months I set the temp and forget it.

 

Yeah, I was on the freeway for some of the time. The EXT TEMP was slowly but surely creeping up towards the true temperature at a constant rate. I didn't count how many seconds it took in-between each degree it changed... but I was convinced the one of the computers was only allowing it to change 1-degree for a certain amount of time... which is a computer programming trick to keep random felonious inputs from sensors from making your system freak out. (similar to how many vehicles won't let the fuel gauge change very fast... so keep drivers from freaking out when you're either going up or down a steep incline and your gauge sudden shows much fuller or much emptier.)

When I was driving home from work this morning everything seemed back to normal. I set it for 72, and that’s what it gave me the whole way home.

 

I had all kinds of problems (now fixed) with the A/C and auto climate control. My service rep finally found out that the Ext. Temp indicator ha no bearing on the functioning of the auto climate control (we thought that if the Ext. Temp was reading too low, the A/C would not work right). Anyway, the Ext. temp is programmed to increment UP in temperature 1 degree per HOUR when you are driving under 20mph. Over 30, it will increment 1 degre per minute until it is accurate. This is to avoid ambient heat from the radiator influencing the temp. Interestingly, if the actual temp is below the reading on the ext. temp readout, it will update rapidly even if the speed of the truck is low. All computer controlled -- geez -- all this just to get the external temp!)

Hope this helps.

 

With summer in full swing now, my ext temp is now reading 20+ deg low on start up after sitting for 8 hours. Ambient is 88F, ext temp reads 64F. It takes 5-10 miles of 55 mph driving for it to catch up to ambient (20 min.). Strange programming.

In the winter, ext temp is usually right on.

 

when it gets below 20f the ac lite will go off. when ac is on at all lite will be on. 40 outside with your temp set at 72 ac lite will still be on with auto. colder than a well diggers *** and lite will go off. this system when working properly is way smarter then u or me. yours is working properly. u lucky people that live in mild climites will never see your ac lite go off. just the nature of the beast.

 

You won't. On a vehicle this big, the load that the a/c system puts on it is quite small in comparison. On a smaller vehicle you would see an impact. I lost a few MPG with my saturn. But you figure that it takes 5 hp or so to run the compressor, that's a big deal to a 127hp engine, but not a 300 hp engine (or a torquey motor like a diesel). Years ago you would see an impact on bigger motors and cars because the A/C compressors took so much power to drive them. Much more efficient systems today.

 

The biggest issue I had with my EATC on the SHO I owned for almost 16 yrs was that it went from 65 to 60 on the temp scale. I often wanted the ability to blow cool air sometimes when it was cool out if I was hot from working hard or working out. Your choice was Ice blast or heat. Now that I have the 05 F250 with the EATC I see it is the same. Ah well...

It always took time for the ext temp to stabilize as it was mounted in front of the radiator in the SHO. Needed airflow to become accurate. Sitting in the sun made it look hotter than it really was, but after a couple mintutes driving it was good. But it wasn't a 1 deg/ min rate by any means. My new 250 seems similar in that regards, as best I can tell.

FWIW

 

My 2007 does the same. Boy, that answers alot of questions.