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2005 Sienna AC Evaporator Temperature Sensor

3379 Views 41 Replies 13 Participants Last post by  3Wheelerguy
Hey guys, first time question. I took my 2005 Toyota Sienna into the local trusted mechanic and got a high quote to fix my ac. They determined that the evaporator temperature sensor is faulty and said that the only way to get to it is to remove the dash. Anyone out there that can point me in the right direction to where this part is located? I am going to do the work myself, and want to remove as few parts as possible to do it.
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It could be this part. Not sure, ok?
Yes, from what I have seen online that is the part. Any additional images about where this is located relative to the glove box?
I wish I could say where it is located but let me ask you this. What is happening to the ac system? You are the first with this problem that I know of since I have been on this 2ng gen forum
Great question. Currently the AC runs cold, but it cycles in and out. When it starts to run warmer I can still tell the AC is running by feel (air does not feel humid) then cycles back to cold again. This happens randomly and does not appear to be repeatable with anything I do. I am not sure how a tech would determine that this is the issue. His notes do state that the ac system otherwise was running well with good pressures.
How much was the quote to fix this? And I'd check with them on how exactly they determined it's the sensor before they start, if you go with them.

You can look at the actual evaporator temp sensor info with the Intelligent Sensor, which I unfortunately do not have (at least yet). If that temp sensor info is giving wacky temps, then yeah it's probably bad, or at least the wiring to it is. But the only way to know for sure is to pull the sensor and check it directly. That's outlined here: Toyota Sienna Service Manual: Evaporator temperature sensor - Air conditioning
So I just called them to learn a little more about how they know that this is the failure, and the tech explained that after checking everything else related to the ac, he was able to "wiggle" or somehow move the part in question and the system returned to normal when he did. So to be clear they are saying the failure is either the sensor, pigtails going to it, the plug, etc. They only way they feel confident is to pull the entire evaporator which is why the price tag is so high.
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Yes, the probe extends into the evaporator core but I’m 99.44% sure the sensor is accessible without splitting the air handler.

Here’s a picture from the passenger footwell of our ‘04 LE with basic AC after removing the inner kick panel. Hold the outer ring of the clip while turning the center counterclockwise with a Philips screwdriver. Once the head lifts the slightest bit, you can pull off the panel sending the clip flying.

View attachment 57464

The yellow and green wires go into a connector off screen then emerge as black wires in the blue sheath. They go into the evaporator housing through that u-shaped thingy that conveniently fits in a 10mm spanner/open wrench. The scuff marks are from the wrench slipping but it seems a counterclockwise turn releases the sensor. I’d have to see a replacement sensor to guess how it’s held.

‘04 LE FWD 198K miles

This is exactly what I was looking for! They said they were able to wiggle the wire and eliminate the issue, so having easy access to this makes complete sense. I have not tired to do the counterclockwise turn yet, today I was gathering more data. I can say at least that for whatever reason the issue is not presenting itself as obviously right now. I tried wiggling and pulling on the wires myself with the car on, but could not create a direct correlation. If I can replace the part as easily as turning this counterclockwise I think I will just order the part and do it, its $16.
Next time on the road while the system is on and cooling report back what the temperatures out of the drivers side and passenger side vents feel like . I'm talking about the vents by the radio. Is one warmer/cooler than the other? Which, if so?
By the way , what level trim ? CE , LE, XLE?

With your question and some time during lunch today I hooked up 4 thermocouples to all the vents on the dash (driver left and right, passenger left and right) and plotted the data for about 30 min. No major failure was noticed while I was driving but I did notice smaller fluctuations. You can see in the plot below that during these smaller fluctuation whatever it was affected all the vents. To have something to compare it against I did unplug the sensor around 8-9 min into the test, then plug it back in. That is the major spike in the middle.

The pattern of failure times is very cyclical, every 30-40 seconds. It is as if the ac seems to fail but before it becomes more noticeable it recovers. I did try and wiggle the wires but cannot remember exactly when so its hard to attribute any small change to that. I will do a better job next time correlating the time when I am doing something different.
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When it happens, how long does it stay warm for? My AC will slightly warm up every so often, especially noticeable when it’s really hot and humid out, but it only lasts a minute or two and then is right back to ice cold. I think this is normal and part of a “defrost” cycle to keep the AC from icing up.


I am really not sure, you might be right. I just posted some data so you can see how often this happens. I have been in plenty of cars that never have these fluctuations, so I am thinking that something is wrong. These small fluctuations are also not the main issue I am dealing with. There have been other times where the AC stopped blowing cold for hours.
I always thought cycling A/C like this was either a slipping belt or a failing A/C clutch? An additional thought is, do you happen to have a loaded van with the digital temperature controls? Lastly, is it possible that maybe one of the common failure points (i.e. blend door servo) is the cause? It's not that ultra-rare failures don't happen in a 17 year-old van, but I think I'd actually take the van to a Toyota dealer and have them investigate the problem (without telling them the proposed solution) and see what they come up with.
We are driving around without it being loaded up, and this is happening. The belt door is also a thought I have had. I had to replace one already (the one that is accessible from the driver side). I believe there is another blend door that is accessible from the passenger side, but I have not replaced that one yet. Do you know what the passenger side blend door does? The driverside if memory serves changed the mode of the van's ac (blowing at feet, or face, or both) does the passenger side combine warm and cold air when the car is set to anything other than HI or LOW?
The wires for the sensor do come out the side of the box. The sensor itself is pushed into the core via a holder. Only way to get it out without spliting it all down would be to cut a hole in the side and fish it out. Glue it back together.
Is there anyway you can give more information on what the holder looks like? I have no problem saving the money by doing exactly what your talking about (or something similar). I wonder if anyone out there has one of these in a wrecking yard so I could get a look at exactly what is holding it in place.
Hmm. Well if it can be reached from that plug, that's great news. According to the images at it looks like there's just a little plastic prong that shoves into the evaporator fins. Still seems unlikely you could reach to remove/replace it through that tiny hole. But I suppose another way, if that isn't possible, is to carefully cut a big hole in that plastic for more room, then just patch the hole up later.

I think by "loaded" he meant do you have a trim with digital temp controls and split zones vs the simpler single zone with simple analog dial temp control.

Ohh, data! I love data. I'm a Test Engineer, and sometimes people will be talking about this or that could be the issue, and I just go and hook up a scope or something else and be like "here's what it's actually doing.

So, you've got the temp data. But we've got more data:
View attachment 57476
It's just a thermister. It says to remove it to test, but if you just run your vents with the AC off and you have the temp of the air blowing through the system, you could measure the sensor with it installed, since accessing the plug is easy.

Also, I'm pretty certain the purpose of this sensor is to shut off the AC if the evaporator starts icing. So you could do another test by sticking a resistor in the mating plug of the temp sensor (the side running to the control unit) to "fake out" the sensor and see if your AC runs without turning off. If so, it's definitely the sensor or wires to the sensor. If it continues turning on and off, and the resistance measurement of the sensor was good, then the issue is wiring downstream from the sensor.

I'd use something like a 2 kΩ resistor for this test, which will tell the car the evaporator temp is ~70 °F so the AC should not shut off (for this reason) with the resistor connected in place of the thermistor. And yes, I've totally used regular resistors to fake a temp to test things at work in place of termistors before to feed the sensor a temp I want it to see without needing to get the actual thermistor to a specific temp.

If you don't have access to a resistor easily, well, you said the new thermister is $16 so alternatively you could just order a new thermister, hook it up and leave it dangling in midair for the same sort of test.
More data...

I overlayed the previous test with the 2k resistor in place, and here is what I got. A lot less on/off cycles it looked like to me. It felt more consistent too. There are still some fluctuations in there but I am assuming that is just part of the system. What do you think? I did try to measure the resistance with the AC running but the temps are moving so quickly up on this 110F day that the values just move right along with it. I did not see any glitches at least. Is it possible that its just doing its job? During all of these tests I have the AC as low as it will go.

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Some more questions. What was the cabin air temp when you took these AC readings? And how fast were the fans running? If you were running the fans at a low speed, does running them on high cause a change in the frequency of the temp spikes? Your shop said wiggling it fixed it, so it sounds like a bad connection (which the resistor/new thermister not installed test I mentioned above can rule out), but if the spikes reduce in frequency or go away with fans on high but not with fans on low, then it may be actually getting too cold (or the thermister has drifted and is not reporting the correct temp anymore so it's constantly hitting the cutoff temp repeatedly).

If fans on low vs high doesn't change the rate of frequency spikes, then definitely a flaky connection I'd say.
I have always had the AC on high, and the fan blowing on high. Cabin air temperature is right at 74 degrees F, and I am pulling from inside.

The latest test with just a 2k resistor in place of the sensor did take the spikes away. Feels like I should just replace it and see if it improves, what do you think?
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