Turn A/C Off When Knob Turned to Max...

mws4ua, The feature being discussed in this thread is unique to 2009 and 2010 model trucks. Your profile says you have an '06.

 

Oh... sorry... My truck isn't super-special... I'm just super-stupid.

Thanks.

 

It happens to everyone. Btw, I do enjoy your humor. In other threads I have busted out laughing at some of your posts.

 

LOL...surprised there's not a TSB out for the AC button yet...I will pull the button trick on the wife; it'll drive her nuts if she can't figure it out!

 

Does anybody just roll down the window anymore ?

OZ

 

Just because the light is on doesn't mean that the compressor is running. There is a whole slew of sensors that determine the load on the evaporator core and toggle the compressor on and off as needed. If it was running the whole time your evap core would trurn into a giant iceblock and you'ld get less air fow and, actually, less cooling.

BTW, what's the point of a Max A/C setting that only turns on the recirc? If you are selecting Max a/c doesn't that meant that you wanta/c?

 

That is all true. But according to a Toyota tech document it clearly states that the compressor is always on while the Air Mix Switch is set to Max A/C mode.

It also states that we should be able to control the compressor with the A/C switch. jmed99 has reported that pressing the A/C switch has no effect. My testing is inconclusive, but I can state the A/C switch stays illuminated when depressed while in Max A/C mode.

It turns on the compressor and enables recirc mode.

 

This is absolutely false! The compressor does NOT toggle on and off if the A/C light is on. Trust me on this...you are in full control of when the compressor is running. This is why leaving the A/C on but turning the temp a little less cool will result in worse gas millage than just toggling the button on and off every so often. The evaporator core (throttling valve) will NOT turn into a giant ice block if the compressor was running for a long period of time.

If you want Max A/C then yes it should turn on both recirc and A/C but give you the option to turn them both off. It does give you the option to turn off the recirc but not the A/C. You should have the option to turn them both off. Actually, having "max A/C" on the temp knob isn't the best design.

 

Now I see the problem clearly. You may be a mechanical HVAC engineer or whatever but you are being ignorant. What I mean by ignorant is uneducated about AUTOMOTIVE HVAC. You are trying to apply what you know about home or commercial HVAC to cars.

Most vehicles on the road today toggle the AC compressor. Even vehicles that use an H-block can still cycle the compressor when required. No input from engineers required.

 

This is funny. Man, I wasn't trying to be arrogant at all....sorry if it came across that way. There's no real right or wrong here as I just wish the knob wasn't tied to the button and I'm looking for a mod to untie them. Others on here wish we had the same mod. You may not want this mod...who cares...there's no right or wrong here.

Ignorant about Automotive HVAC????? lol I wont even go there. I don't know you and you don't know me so we probably shouldn't call each other ignorant. Thanks for the laugh though.

Even if our HVAC did toggle on and off (even though the toyota documentation says it doesn't ) it would be impossible for it to toggle on and off depending on our comfort level so it wouldn't be doing it in the most optimum way.

Not trying to argue here....I'm just looking for the mod and you don't want such mod so I'm not sure why you even care.

I bet it would be easy to untie the two but I know most people don't wanna try in case we screw something up. I sure don't but I thought it would be worth asking if this existed.

 

Didn't this thread start by someone asking how to just get fresh air, vented from the outside?

I have a 2010 and also found it strange that when I turned the temp knob all the way to the coldest setting (without touching any other button) that it forced the AC system on. It's almost like the Government these days. Giving us stuff that we didn't ask for nor do we want and which are going to cost us more $$.

So I guess the answer is to just turn the temp knob to one notch less than full if you just want fresh air vented from the outside, correct??

 

I was only being a little funny. There is a reason why just about every automotive HVAC system will cycle the clutch on the compressor. It is because they do not use (for the most part) a traditional sump type lubrication for the compressor. If the R134 gets low and the pressures drop it can starve the system of lubrication. So we cycle the system off. Many newer systems can also cycle the system off if the high side gets too high as well. Add to that the thermistor on the Evaporator and it can turn off the compressor to prevent ice formation. Heck, for years Cadillac would set a code and disable the AC compressor until the vehicle was checked and the code cleared. They would also not allow the compressor to even come on when the ambient temperature was below a certain point. EVEN with the system set at MAX and the AC button depressed. If you let the car warm up, it still would not run unless you commanded it with a scan tool. The data from the ambient temp sensor would not start to update until the vehicle was driving 25 MPH. The data would go live at 45 MPH. Once it saw the warmer temperature, VIOLA, the compressor would come on. To stay on topic with our vehicles, the compressor even has a speed sensor in the compressor. If the compressor RPM is not logical with engine speed, it assumes either a slipping belt or clutch and can disable the compressor to prevent additional damage.

My truck cycles the compressor on and off with the system set to MAX AC. It is a 2010. Now I guess you want a video to document it? You want documentation, I suggest you purchase the repair information for the system. Look at the schematics and the symptom based diagnostic charts. Then you will see how the system works.

Not trying to be mean, sir. Just pointing out the facts of the system and the differences between cars and buildings.

Yes, Pyriteship. jmed99 is the OP and he asked the question. He has made some assumptions about the system and that is what we are discussing. With respect and a little humor, I hope. It is the age old engineer and technician discussion.

Yes turning the knob back off the detent will get you button control. As far as a MOD would go, that would take me a little while to stare at and think about. The inputs are variable resistors, diodes and switches into what is basically a logic module. So knowing what to change or what value to prevent for the AUTO MAX AC mode would take some time to figure out. I bet a person that specializes in electronic control systems could look at the schematics and figure it out faster. In my job, I fix existing systems and run the tests as designed. The simplest way I can see to override the AC compressor coming on would be to put a toggle in the ground side control for the AC clutch relay. Then if you went to MAX position and the toggle switch was open the compressor would not come on. The potential problem with that would be the RPM sensor in the compressor. If the logic module thinks it commanded AC and then does not see any RPM from the compressor, it may set a code and get an attitude.

Fun stuff, eh?

 

hahaha you guys need to be "civil" engineers and technicians!
Did you ever see that commercial for the phone book and finding civil engineers?

If you figure it out let me know as I don't like the way it operates either. But I'm also one of those lazy guys who gained a few pounds by not reading the manual to find out I could just go one click back to vent!!!

 

I think we may be able to mod this pretty easily by bypassing the Max A/C position out of the system. We can make the mod to the Heater Control Panel Assembly. A detailed inspection of the Air Mix Switch would be in order first.

If your interested in the system diagram click here

 

I'm to skeered to try it....lol! Let me know what you find!

 

A/C MOD (search for it) Great one! Stops the Compressor from running all the time in defrost..proven quit arguing.

My A/C and compressor only comes on when I push the A/C button...mpg gains and no more confusion with the dam A/C button coming on when its cold out etc..

 

I have two minor mods ahead of this one but I promise I'll investigate it. I need to get the wiring diagram for a 2009 too.

Haha I've taken apart my taco before. The wife raised some eyebrows over this one.

On my dash on the driver side you can see the heater control panel assembly, the one we need to inspect.

 

I'm skeered too - For now, I just need to find my "detent"

 

Ummmm, now I see WHY I'm scared.

 

It looks more scary than it is. Those papers in the photo are the instructions for the dashboard assembly. I got them from TW and they worked great. I couldn't have done it with out them.