Hidden A/C feature to prevent engine overheat????

Here's something for you techies and those that like "hidden" features on the Tacoma. This one happened to me three times under the same conditions however on the third time it happened (today) I had a Scangauge and was watching things and found what I consider to be an undocumented feature of the A/C system that helps prevent overheating.

Today it was 107 degrees where I live so the A/C was in full force use. Normally the coolant temperature of the truck runs about 190 degrees consistently when the outside air temp is 90 or less. Today the coolant temp ran about 195. Unfortunately though I live in California in one of the worst commute areas and today of all days some yahoo decided to crash and block traffic for a couple miles on the freeway. That coupled with the fact that I ascend a 1000ft pass which is about 5% grade made things even more interesting since I was crawling at <5mph. Soo.. watching the coolant temperature out of curiosity I slowly watched it climb to 200+ but an interesting thing happened at 213degrees. At 213 I heard my A/C recirculate damper close and sure enough I looked down and the recirculate light was on. Pressing it would not allow me to turn it off but pushing the A/C button shut the whole system down. I turned it back on though because it was hotter than heck outside. It was still getting cold as well. At 220degrees though I noted that the A/C compressor cycled off and when it did the recirculate light turned off as well. Warm air started coming out of the vents as well but not for long. When the A/C compressor turned back on the recirculate light turned on again as well. This did this about 5 times before traffic strarted moving faster. Although I was still climbing the pass but now about 40mph the temp dropped back under 220 and the A/C no longer cycled. Once the coolant temperature dropped below 213 the recirculate light turned back off as well and everything started getting cold as normal and the button functioned fine as well.

Previously when I didn't have the Scangauge I automatically paniced and thought the A/C unit was malfunctioning and simply shut it off and opened the windows. Since I had the scangauge I was watching the coolant temp and the needle to see how far it would go before the needle rose up. It never really did move so I just left the A/C on to see what would happen.

Sorry for the long post but I thought some might find this interesting should you happened to be in really hot weather and find your A/C doing funny things. I personally think it's a great function so if you forget to turn off your A/C when climbing grades on hot days then the system will take care of itself. Don't have to worry about those signs that say "turn off air conditioner"

 

I dont have a scanguage, but my '01 actually runs a little COOLER with the AC on! One thing I notice on my truck is the clutchfan spins a little faster with AC on-you can hear it.

 

Good info thats a good thing for our trucks.

 

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It makes boatloads of sense....(imagine that - toyota engineers aren't bad afterall).

Thanks for the info!

 

Yeah,Glad i caught that.Around here,driving w/out a/c is not an option.So far i've seen 119 on the outside air temp.in the truck.

 

Ya my Mom lives in Laughlin - two seasons - Summer and Christmas!!!

 

lol,That's about right.

 

How can the clutch fan spin faster - it it nothing but a silicone clutch, and tied to the engine - Now, some have a temp sensor in them that do make the clutch slip less as the temp in the engine compartment gets higher.

 

" Today it was 107 degrees where I live so the A/C was in full force use."

But you don't normally recycle the inside air?? AC Works much better that way - I always do that around here.

 

I don't know-explain to me why I hear the fan "rushing" more air when the AC is on?

 

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A very simplified explanation of a viscous fan drive would be imagine a manual trans clutch and p/plate, but fill the enclosure full of oil. In the fan clutch the disc ius the shaft of the fan clutch, the p/plate is the inside front cover. With the two seperated by a .050 gap the fan will spin slower than the shaft speed due to the shearing of the fluid, move the two plates closer to each other, mabey .005 and the fan will spin almost (~85-95%) the same speed as the shaft due to the fluid. Most automotive fan clutches don't actually move the plates in and out, the bi-metalic spring that rotates the small pin in front of the fan clutch lets more fluid in to fill the space, or opens a passage to allow it to spin out by centrifical force into a cavity inside the outer perimeter of the clutch body. In the morning during a cold start; all the fluid has settled out and takes a few min for centrifical force to do it's job. I have seen cutaways before, but back in 1979, I replaced the fan clutch on a 64 GTO I had, and cut the old one open on a machine shop bandsaw about 1/3 across the face, and made my own cutaway where the shaft could still be rotated. That fan clutch was made the 49th week of 1963, but it looks, and works just like the ones made today.

EDIT: An easier to understand view might be obtained if you could find the old, really old pics that most books show to explain how a viscous coulpling works; the pic used to show to common electric fans facing each other; 1 on and 1 off. The operating fan will cause the non operating (off) to spin; move them apart a bit and the off fan will slow, move them closer together and the "off" fan will speed up, but never at the 100% level due to the inefficient design.

 

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Basically what I had stated earlier and changed my mind about it and deleted it; Why would anyone be running the system on outside air @ 107º?; The heat load off the condenser is probably why the engine coolant temp went up as high as it did. Toyota's are sold in most every hot, hostile desert regions of the world, and don't get close to overheating because the drivers know to change to recirculate, so the 60º+ output air can be 40-44º air, and at the same time allow compressor an occasional cycle off, be much easier for the engine to turn (once head pressure is down) thereby saving fuel, and lessen tremendesly, the heatload transfered to the radiator and the intank trans cooler.

 

When the AC compressor engauges the engine RPM's rise a bit. This is probably what you're hearing. The compressor takes power to turn and it needs to turn at about 1000 rpm to do much good. The truck's computer knows this a gives the engine a bit of gas when the compressor comes on.

 

Despite the mechanics which are obvious... for me personally I don't like to run on recirculate because for me the air gets stale. I'm one that may actually crack open a window with the A/C on just to get some fresh air inside. Most of the time I drive will my windows open until it gets too hot. Personal preference I guess.

 

Yeah I know about the throttle adjust and all...and I appreciate the huge effort from LRH...but this all doesnt change the fact that when I turn on the AC, there's more of a rushing of air thru my fan-like a school bus or bobtail makes. I usually have that sound when I coldstart for about 45 seconds then it goes away. Well anyway my original point was that my truck runs a little cooler on the gauge with AC on. I love whatever they did in this truck to achieve that!

 

Oh, ok. What you're experiencing is the fan coming on when the AC is turned on. A lot of vehicles do this. The water temps may not be high enough for the fan to come on, but the fan is programmed to turn on any time the AC is on. So you're hearing it come on when it was off before turning on the AC. Many fans will run initially on a cold start if the fan was running when the engine was shut off.

 

But I have a constant clutch fan on the engine-not an intermittent electric one-may as well forget this one-it's not important enough to beat around thanks though.

 

I'm not sure if this is related, but my 05 AC has not come on at all when I have started the truck. Twice I was in Houston in dead summer with 90+ humidity, the fan would not blow or do anything, my AC and Recirculate buttons were still lit. Then after a while the AC just kicked back on with out me doing anything.
Today it is easily 100 here in Fort Worth and my AC has done the same thing, except this time it will not come on for the life of me, I have parked it in the garage to cool off, but nothing. I have noticed that I still lose RPMs when I turn the knob, but nothing, no hot or cold air. I've checked fuses, any suggestions or help?

 

I've had this happen once during the first week that I've owned my truck. I had like 200 miles on it. I took the battery connections off during my CAI instal and after that is when it happened. The A/C button was lit and there was no cold air but there was hot air. It was a hot day so I left the the a/c button on and after 20 minutes of driving, it just turned on and have had no problem ever since.