Any way to turn AC off when in defrost mode?

[OrdnanceMarine]

I'm fairly new to the 4Runner and to this site and after scouring threads via the search function for hours I still haven't found a solution. Is there any way to disable the AC compressor while in one of the defrost modes?

I know why it engages automatically but I want a way to disable it myself as 95% of the time I don't need the compressor running to take care of a little condensation. Additionally, my ScanGaugeII shows about a .3 gallon-per-hour increase in fuel consumption (about 40% of idle fuel consumption) with the AC running. This equates to about an extra $1/hour to run something I don't need.

Does anyone have a fix for this? My Hondas have either just allowed me to hit the AC button to disable the compressor or I had to enter a series of buttons to make this possible. Any chance this is a CBEST option?

 

[THEROK]

my ScanGaugeII shows about a .3 gallon-per-hour increase in fuel consumption (about 40% of idle fuel consumption) with the AC running. This equates to about an extra $1/hour to run something I don't need.

you sound like KIT here. awesome.

 

[OrdnanceMarine]

you sound like KIT here. awesome.

Love of numbers, I guess. As an engineer it helps out at work and as a DIY'er geek who's installed his own solar panel system it helps out at home!

 

[thirstyturtle]

I have a 2006 Sport V8 4x4 and my AC doesn't kick in when the defroster is selected. I don't know if the previous owner did something to make this happen or not. On my 2002 Acura RSX-S there was a sequence I performed with the knobs and the ignition to enable me to turn off the AC while using the defroster, maybe there's something similar for the T4R?

 

[scottm]

On most (all?) modern vehicles the AC kicks in to dry the air in defrost mode. On my '03 the AC doesn't kick in for the defrost and foot heat mode, but is latched on for defrost. You could pull the fuse for the AC, but then wouldn't get the extra-dry air for defog, which really does help.

I agree I don't like running the AC when it doesn't seem necessary, wear and tear as well as mileage. On my Land Cruiser I have to deselect it or it runs almost all the time, even in snowy weather. It's a luxury thing, de-humidifying the air.

 

[JB.]

Is there any way to disable the AC compressor while in one of the defrost modes?

So, with A/C off and the fan blowing manually, you select defrost. Are you saying that the A/C light comes on at that point, or that it stays off but the ScanGuage reports compressor operation?

 

[OrdnanceMarine]

I missed posting this last night. Forgot to submit it after previewing.



I went ahead and bought the electronic version of the factory service manual for reference. In section "E.W.D. 2007::2007 4Runner: Air Conditioning"
On page 365 under "System Outline" it states:

6. Air Conditioning Operation
The A/C control assembly receives various signals, I.E., the engine RPM from the engine control module, out side air
temperature signal from the A/C ambient temp. sensor and coolant temperature from the engine control module, etc.
When the engine is started and the A/C SW (A/C control assembly) is on, a signal is input to the A/C control assembly.
As a result, turning the MG CLT relay on, so that the magnetic clutch is on and the A/C compressor operates.If the A/C control assembly detects the following conditions, it stops the air conditioning:
∗ Evaporator outlet air is too low.
∗ There is a marked difference between the compressor speed and the engine speed.
∗ The refrigerant pressure is abnormally high or abnormally low.
∗ The engine speed is too low.
∗ Rapid acceleration occurs.

This makes me wonder if I could install an override switch for the clutch and only enable it when I want the AC to run. Other options would be to look in to how the system determines if any of the 5 criteria to stop the air conditioning have been met and manipulate one of these.

Anyone messed with any of this?

 

[obxfishn]

This is what I did when I had my Tacoma, The 4Runner should have the same diagram but should you decide to do it, do so at your own risk. This mod worked on my Tacoma nd I plan to do it to my 4Runner soon.

A/C on with Defrost - Tacoma World Forums

 

[obxfishn]

Since the Tacoma and 4Runner are so similar as far as engines and wiring, here is a linky to a website that has a lot of great ideas for mods. When you getr to the link, scroll down to the "Mods" section for a wholw hoat of mods for your SUV.

Cheap/free mods - Tacoma World Forums

 

[810moto]

i just push the a/c button and turn it off and let the defrost run. works for me

 

[OrdnanceMarine]

i just push the a/c button and turn it off and let the defrost run. works for me

I have yet to find a way to keep defrost on without the AC cycling. I'm trying to see if auto will make me happier with the climate control system but when I select defrost it kicks it out of auto and turns the AC on. I'll toy with it a little more just to be absolutely sure but from what I've been reading it seems like another case of Toyota being my mom.

 

[OrdnanceMarine]

This is what I did when I had my Tacoma, The 4Runner should have the same diagram but should you decide to do it, do so at your own risk. This mod worked on my Tacoma nd I plan to do it to my 4Runner soon.

A/C on with Defrost - Tacoma World Forums

Looks like a small project to try over the next week or so. I'll do a little more looking around and I'll probably end up giving it a shot and if it works then I'll put a small switch somewhere in the dash. Thanks for the heads up!

 

[Larry77]

I thought with the newer cars the MPG loss when running the AC was very minuscule? 3mpg sounds like our old school cars...

 

[OrdnanceMarine]

I thought with the newer cars the MPG loss when running the AC was very minuscule? 3mpg sounds like our old school cars...

I'm seeing a .3 GPH increase at idle when the compressor is actually running, which is probably 2/3 of the time. I tend to average about 20 MPH in town, getting probably about 18 MPG during this time (the dash display reads about 10% more optimistic than my ScanGaugeII and the fill-drive-fill manual calculation show). I come up with a fuel burn of 1.1 GPH (20 MPH/18 MPG) of which a .2 GPH increase (2/3 * .3 GPH) is an 18% increase in fuel burn bringing 18 MPG down to 15.4 MPG. This situation represents what I've come across most often. If you use a highway situation where you're averaging 65 MPH, getting 23 MPG (2.8 GPH) a .2 GPH increase starts to drown out as a 7% increase or from 23 MPG down to 21.7 MPG.

I wonder if increases in system efficiency have been countered by decreases in the efficiencies of the refrigerants that EPA laws require.

 

[chaz]

i do what 810moto says, seems to work.

 

[TechWrench]

i just push the a/c button and turn it off and let the defrost run. works for me

Ditto, this works on my '03.

 

[Maritimer]

Just for interest's sake, on my 2001, when I put the window air on, even though the green A/C light doesn't come on, it seems to be taking water out of the air, as it drains out onto the driveway from a little spout near the exhaust outtake from the engine. Kind of between the front right wheel and the engine.

 

[OrdnanceMarine]

i do what 810moto says, seems to work.

Ditto, this works on my '03.

Tried it over and over today to validate and no matter what I do, the compressor still cycles if either of the defrost settings are selected. The fact that the AC light isn't on does not mean that the compressor isn't cycling.

Maritimer's observation seems to show that his version does this as well.

I don't mind Toyota programming the system to automatically turn the compressor on when you select defrost, I just wish they gave me the ability to turn it back off.

 

[TechWrench]

Tried it over and over today to validate and no matter what I do, the compressor still cycles if either of the defrost settings are selected. The fact that the AC light isn't on does not mean that the compressor isn't cycling.

Maritimer's observation seems to show that his version does this as well.

I don't mind Toyota programming the system to automatically turn the compressor on when you select defrost, I just wish they gave me the ability to turn it back off.

The A/C compressor cycling is a normal occurance, even if the A/C isn't selected. It is done, on most vehicles, in order to keep the compressor from seizing up from long periods of non-use. The slight extra cost to do this is a small price to pay to help prevent compressor failure and the cost to replace it.

 

[OrdnanceMarine]

The A/C compressor cycling is a normal occurance, even if the A/C isn't selected. It is done, on most vehicles, in order to keep the compressor from seizing up from long periods of non-use. The slight extra cost to do this is a small price to pay to help prevent compressor failure and the cost to replace it.

Can you show me something from Toyota that states this? TB or their service monthly, etc? I've never seen a vehicle that would just out of the blue start running the compressor as a means of self-preservation. I've seen plenty of owner's manuals that specifically request that you run the compressor for ~10 minutes each month to ensure the seals, etc. stay lubricated. Most of my cars go a month at a time without the compressor running for 7 months out of the year. The fact that the compressor cannot be turned off in the defrost mode has nothing to do with longevity of the system. In fact, spending all of that unnecessary time running can only hurt the longevity of the system.