You are currently viewing our boards as a guest which gives you limited access to view most discussions and access our other features. By joining our free community you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is fast, simple and absolutely free so please, join our community today!
If you have any problems with the registration process or your account login, please contact contact us.
TacomaGeneral discussion forum for the 2005 and later Toyota Tacoma.
This is a discussion thread titled "Defroster-linked Air Conditioning", within the Tacoma forum, part of the Truck Forums category.
Okay, I'm just going to put this out there as a good reference. I've mentioned this before in a different thread and got others arguing about the accuracy of this. Part of why I want to put this out there is because the owner's manual is wrong.
When running the heat setting to floor/defrost or defrost-only, the owner's manual says you can press the A/C button to run the compressor to help clear moisture out of the vehicle. This statement is wrong.
I always knew that the A/C compressor would come on at these settings with the fan turned on (as has been the case in all my previous Toyotas but the light usually came on), but I never tested whether there was a way to turn it off. Others in this forum think that the A/C light must be on for the compressor to run, but that's simply not true. I just spent some time seeing if turning the A/C light on or off had an impact.
After testing all scenarios, there is no way to turn off the A/C compressor when the heat setting is in either of these 2 positions (and the fan is turned on). I tried pushing the A/C button so the light was on...compressor still running. I then tried turning it back off...compressor still running.
End result, A/C is linked and will run regardless of what the owner's manual says. Also, this will impact gas mileage in the winter.
__________________
"It's not what you know. It's knowing where to find the answer."
'05 4x4 DC LB SR5 Tow Pkg BFG All-Terrain T/A KO, Leer Tonneau, Westin Platinum Nerf Bars, Fog Light Mod, Orig. Owner 12/3/04
Last edited by 05Moose; 12-20-2007 at 05:14 PM.
Reason: Forgot to add the impact to mpg
YO Moose: It's currently spitting rain and snow where I am and so I can't go out in the driveway and check your findings on my truck. As I mentioned in the last thread on this topic, I still have to figure out HOW do they do it....engineering wise. You are gonna make me dig out my texbook on the "Refrigeration Cycle" to see "WHAT" is going on. I can't remember where the book is, as it's been 40 years since I took thermodynamics.
In the old days when they used Freon 12 as the refrigerent, (No longer legal) the compresser compressed the Freon GAS into a Liquid. (Freon is a GAS at room temperature, and standard pressure.) Compressing any gas makes it very hot, so the heat has to be removed next. This is done via the radiator-like device in front of the engines radiator....if memory serves. Now the LIQUID Freon (still warm, but much cooler than before) is piped to the condensor (a little radiator in the A/C unit which is mounted on the firewall..usually, where the Liquid Freon is allowed to (flash) ...ie EXPAND Rapidly back into a gas which makes it very COLD. Outside Air, or cabin air, is passed through the little radiator which cools the air and is sent into the cabin. I hope I got this right.
NOW I have to figure out HOW Toyota "HEATS" the air for defrosting...and what would be the point of using the A/C to make heat when you can use engine heat...and it's FREE.
More later once I can go out and SEE the compressor actually "compressing", and not just "freewheeling". Is the clutch actually engaged??? Regards: TacoGuy
The cabin air runs over the condenser BEFORE passing through the heating coils (I know, it's another radiator-like thing) so the air can then be heated. All vehicles use this method because that way you can adjust the air temperature of the A/C in the summer so it's not so blazing cold.
The reason they link the A/C is because running air over the condenser inside the cabin dries out the air allowing more room in the atmosphere to store moisture. After heating the air with the A/C on, you can then quickly evaporate the moisture off the windows and from inside the whole cabin (since by running the A/C you've made more room in the air for it to hold the excess moisture). If the air were already completely saturated with moisture, you wouldn't be able to evaporate any of it from inside the cabin...thus the need for the A/C if the conditions are right.
Yes, I looked at the compressor. I tried changing the switch configurations and then checked to see if the clutch was engaged (engine has to be warm for this whole process to work otherwise the thermostat inside the cabin tells the A/C that it's already too cold and it won't kick on). I've always known it came on automatically because you can feel the engine pull when it engages the clutch at a stop light. What I didn't know was whether by hitting the A/C switch on or off whether it made a difference. The answer is no.
__________________
"It's not what you know. It's knowing where to find the answer."
'05 4x4 DC LB SR5 Tow Pkg BFG All-Terrain T/A KO, Leer Tonneau, Westin Platinum Nerf Bars, Fog Light Mod, Orig. Owner 12/3/04
There's a way to disable it by pulling the wire that switches to the defroster. I'll see if I can find it because I want to do this myself. I don't need the compressor cycling. Not like it's going to get the heat any warmer than it already is. It's for cold air only.
__________________
"You can't be afraid to reverse engineer something to see how it works." -Me
Last edited by The Phoenix; 12-20-2007 at 05:34 PM.
There's a way to disable it by pulling the wire that switches to the defroster. I'll see if I can find it because I want to do this myself. I don't need the compressor cycling. Not like it's going to get the heat any warmer than it already is. It's for cold air only.
What I'd like to see is someone finding a way to modify it so that it only comes on when the A/C button is pushed. That would be ideal. There are times when it's a must having the A/C compressor running to evaporate the moisture. But there are many times when it isn't necessary.
We could all use saving some money by getting better gas mileage and only using the A/C compressor when absolutely necessary.
__________________
"It's not what you know. It's knowing where to find the answer."
'05 4x4 DC LB SR5 Tow Pkg BFG All-Terrain T/A KO, Leer Tonneau, Westin Platinum Nerf Bars, Fog Light Mod, Orig. Owner 12/3/04
Last edited by 05Moose; 12-20-2007 at 05:49 PM.
Reason: Forgot something
It would be awesome if someone could figure this out, I know with my Civic, there was this crazy procedure with holding the defrost and the A/C button down while having the fan and temp on a specfic setting and then amazinlgy the A/C was no longer linked to the defrost. Honda did it the same way where even if you turn the A/C button off, the compressor still runs. I'd rather that car manufacturers didn't think owners are morons and make it "idiot proof."
Perhaps if a fault was detected that shuts down the A/C such as an abnormal HIGH or LOW in the refrigerant pressure.
I wonder if pulling or jumpering the refrigerant pressure sensor connector just in front of the power steering resvoir would do the trick? Would the heat/defrost still run? That was the original question wasn't it?
Then it would just be a matter of installing a switch to trick it into thinking there is a fault when you want.
Have to try this this weekend, see what happens.
__________________
Keezer
Silver '05 DC Short Bed 4x4 Auto w/Tow Package
Donahoe Coilovers & UCA's up front
Wheeler's Add-a-Leaf out back
Demello Rock Sliders
FJ Steel Wheels & Nitto P265 TerraGrapplers
This works. I just tried it. Pulled the connector to the refrigerant sensor and left it dangle. Heat came on on defrost but the compressor did not kick in.
So basically, if you want to control the compressor regardless of mode, run a switch up to the cabin from the refrigerant pressure switch and you can trick the system whenever you want.
__________________
Keezer
Silver '05 DC Short Bed 4x4 Auto w/Tow Package
Donahoe Coilovers & UCA's up front
Wheeler's Add-a-Leaf out back
Demello Rock Sliders
FJ Steel Wheels & Nitto P265 TerraGrapplers
This is very interesting and I have the utmost appreciation for the inputs here on this thread......including my own. BUT I almost always have to revert to this: Toyota Engineers didn't get THIS FAR ...over the years by designing superfluous systems...just for the sake of "an excersise in design"...... I HOPE.
Also: I am most likely not as smart as the guys who designed this system. THEY are Current. I am NOT.
This works. I just tried it. Pulled the connector to the refrigerant sensor and left it dangle. Heat came on on defrost but the compressor did not kick in.
So basically, if you want to control the compressor regardless of mode, run a switch up to the cabin from the refrigerant pressure switch and you can trick the system whenever you want.
How about disable REC override, too?
__________________
2005 Tacoma AC 2WD 2.7L 5M
Last edited by lelandstanford; 12-20-2007 at 09:06 PM.
Only the "passive occupant detection system" of the HVAC is Delphi. I'd bet the guts of the HVAC (e.g. compressor) are Denso parts and Toyota has owned the Denso company since at least the 1950's.
Only the "passive occupant detection system" of the HVAC is Delphi. I'd bet the guts of the HVAC (e.g. compressor) are Denso parts and Toyota has owned the Denso company since at least the 1950's.
In the old days you had a problem with the seals drying out during the winter due to the A/C not running, so they changed it to work when you had it in defrost position
This works. I just tried it. Pulled the connector to the refrigerant sensor and left it dangle. Heat came on on defrost but the compressor did not kick in.
So basically, if you want to control the compressor regardless of mode, run a switch up to the cabin from the refrigerant pressure switch and you can trick the system whenever you want.
Able to take a photo of this for everyone to see?
__________________
"You can't be afraid to reverse engineer something to see how it works." -Me
TundraSolutions.com is a registered trademark of Tundra Solutions, Inc.
Other trademarks and brands are the property of their respective owners. Use of this Web site constitutes acceptance of the TundraSolutions.com User Agreement and Privacy Policy.
Defroster-linked Air Conditioning
There are times when it's a must having the A/C compressor running to evaporate the moisture. But there are many times when it isn't necessary.
BUT I almost always have to revert to this: Toyota Engineers didn't get THIS FAR ...over the years by designing superfluous systems...just for the sake of "an excersise in design"...... I HOPE. 
TacoGuy
Linear Mode
