A/C Performance during Highway Cruise

UR right. Very odd!

 

One option is a water hose set to mist. Spray the condenser and that will take the efficiency well north of what you would see at 80mph. You can go a step further with a shop fan set to blow through the radiator as well, but the mist from the hose should be enough. If you have gauges, you should see the pressures drop as a result, at least the high side will drop since the condenser gets ultra-efficient when wet.

 

@will.carroll7 , hoping everything is still 'cool' for you after the fix.......... Had it on the open road yet?

 

After Toyota's fix the A/C does work better and works better but it still freezes up on the highway. I've talked to my local dealer on the phone and they agree that it's probably the evap thermistor that's gone bad. It's a $9 part and I'm hoping I can fix it myself as it would be anywhere from $200-$400 in labor at the dealer.

I've posted more details in this thread:
https://www.tacomaworld.com/threads/2013-evap-thermistor-replacement.447561/#post-13091996

I'm hoping to get some insight on how difficult it is to get to that part before I do it. I figure worst case scenario, if I get everything apart and get stuck, I'll drive it up to the dealer and have them finish it and I've saved them some time.

 

I thought you were still under warranty? No?

 

Warranty runs out Monday. I'll have to see if I can get an appointment then.

 

If Monday is a problem for you (or them) talk to the mgr. about the 'date' and warranty honoring; they have the power to 'extend' the time as it was a reported problem.

They worked on and did not completely fix. If they'd done their job, you'd have rolled out all squared away.

It's not your fault you have to return.

 

I'll call and ask this afternoon. Hopefully you're right. I'll keep this updated when I find out.

 

I just heard back from the dealership. They identified the problem as the evap thermistor (+1 to @Clearwater Bill) and have ordered another one, the whole issue will be fixed under warranty as soon as the part comes in.

 

Final update: Dealership completed replacement of the Evaporator Thermistor No. 1 under warranty and the problem is solved. A/C works great in all conditions now. Thanks everyone!

 

@Clearwater Bill

Old thread but I have this same exact issue with freeze ups and after checking the resistance of the sensor to Toyota specs it confirms it is bad.

I have a sensor on order however I am trying to find someone with knowledge of how I can get to it without taking the dash apart. If the dash has to come out has anyone done that before? I have searched for hours and can’t find video or answers.

 

I thankfully have not had to go digging for mine, so I have no idea how difficult it may or may not be to get to. The last one I changed was on an 80's Honda. Manual called for dash disassembly and all that to access the evap. However that car had a 'split case' that I was able to unbolt the face of the case partially, use some wedges to hold it open and reach / replace the sensor with a few contortions and a really long set of needle nose. It was not bolted in, it was clipped to the face of the evap. When you get your new part, you'll quickly figure out how it's mounted.

How did you check the sensor resistance if you haven't located it? Or is the connection outside the case?

Let's summon @CurtB and @Jimmyh and see if they can offer you any guidance.

 

@Clearwater Bill - the sensor has a connection behind the glove box. I am reading 250-350 ohms when ac is cold, the Toyota charts show it should be in the 2-3k range at colder temps. I think mine is showing warm hence it not shutting off compressor and letting it freeze on long drives. Wish there was a way I could hook up to the computer and see what it’s actually reporting.

I am going to take the radio out today and see if I can get the case open just like you did, maybe I can get it out without removing the dash.

 

I have no clue how to get to that sensor.

 

Until you get it fixed, just shut off the AC periodically and let the fan defrost the evap. Rinse and repeat. It's not ideal but it will get you by til you get it fixed.

 

@CurtB - I have been doing that. I bought the truck used a few weeks ago and on the drive home I noticed it, of course the guy said he never had an issue with it.... my plan is I'm going to give the truck to my son in a year so right now its parked. I have been doing the defrost method on the few trips I made, wife doesn't like it!

I am a refrigeration tech by trade and also work with electronic controls, I know a little bit about whats going on but no means an expert on car a/c's! I started with verifying the charge, I pulled all the gas out, pulled a vacuum to 400 microns, then weighed the charge back in just so I knew that was correct. After googling and thinking through the issue more I arrived at checking the thermistor.

I used the chart below to verify the sensor is bad, I will also measure the new sensor when i get it this week. My sensor is reading around 126 ohm sitting in my garage around 80 degrees. Its not completely bad as it does increase in resistance when the AC comes on.

I can't believe they didn't make this a slide in and out replacement!!! I have a trust issue with hiring anyone because there are so many people out there (any trade) that don't know what they are doing, I didn't want to take this to a dealer and have them charge me big $$$ and still not have it fixed.

 

I discussed this with him in this thread:
https://www.tacomaworld.com/threads/ac-evaporator-thermistor-replacement.668980/#post-23479097

The way it is put together I'm pretty sure it will need to be removed, but it is hard to tell from the videos of the evap replacements I have seen.

Hopefully the poster will let us know when he does the replacement.

 

@Jimmyh @CurtB Thanks for all the info and help so far, I spent a few hours last night looking at a bunch of different threads and looks like you guys are the experts!!

I did a little test today in the driveway...
-Fan on second lowest setting
-AC on Max with recirc
-Outside air - 81 degrees
-Idled the engine to 1300-1400

After idling for three minutes at 1300-1400 the discharge air out of the vent was 27 degrees, I shut the truck down and popped the hood to look at the suction line and it was already icing (expected if evap air temp is that low). From reading posts in this forum someone said that the thermistor is suppose to shut the compressor off at 36 degrees... that coupled with the resistance readings I took is how I am arriving at the bad thermistor. I have had a few people think its the expansion valve but I can't wrap my head around all the data and how it would produce these results even if it was overfeeding...

Looking for someone to confirm with me that its the thermistor causing the freeze ups.... helps me to have multiple minds that agree or disagree.

 

If only you had LP gauge readings. At 27f the LP would be ~15psi. The LP switch should shut off the compressor at ~28psi. I kinda think you have 2 problems, the thermistor and the LP switch. I don't think that LP switch is expensive, and definitely easier to change. I'd try that 1st.

I don't know about a Tacoma, but a lot of older vehicles had a schrader valve under the Lp switch, no need to recover the freon. Just unscrew the switch and screw the new one on. Maybe someone else knows for sure.