2005 Sienna AC Evaporator Temperature Sensor

thescot14 · 2022-07-23

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.

J

jseyfert3

· #21 · 10 mo ago

sixto said:
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.

Sixto
‘04 LE FWD 198K miles

thescot14 said:
Paul,

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.

Hmm. Well if it can be reached from that plug, that's great news. According to the images at tsienna.net 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.

thescot14 said:
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?

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.

thescot14 said:
Paul,

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.
View attachment 57475

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:

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.

Top Contributors this Month