Hey y’all. I have a real head scratcher of an AC problem here. I was hoping this was covered in a previous thread and did my best to search, but came up empty. If I’ve overlooked anything, my apologies and please point me in the right direction.

I’ve had my 02 GS300 for a few years now and the AC has always been spotty but this summer is different. As it got hotter outside, the AC was less likely to work. Sometimes it would be lukewarm, sometimes it blew straight up hot air through the vents. On cooler mornings or if parked in the shade, it was more likely to blow cold. But that wasn’t a sure thing. Finally as we hit mid July, it cut out altogether - hot air only. Seemingly, the hotter the car is allowed to get inside the cabin (which can be really hot here in Tennessee), the hotter the air coming out of the vents. The fan speed and mode buttons work great, but the temp control has no effect on the driver or passenger side.

I took it to my mechanic and he found it was out of Freon. He gave it a recharge, put in some dye, and told me to come back in 2 days to find where the leak is. It was blowing ice cold in their garage after the recharge. I take it home and park it in the driveway overnight. The next morning, it’s already noticeably weaker. I run an errand with it, after which I start it up in the parking lot and find the A/C is ice cold once again. But by the end of the next day, it’s back to hot air (like a blow dryer!) while I’m on the interstate.

I drop it back off with my mechanic the next morning. At around 5:00 pm he calls to tell me that not only is there no leak that he can see, but when he pulled it back into the shade of the garage, the compressor kicked back on and it started blowing cold again. He said he can’t figure it out and doesn’t want to do anything that involves getting behind the dash because it’s expensive + time consuming, and things often break in the process on an old car. But he suspects it’s something electrical. He is sure that it’s not the compressor.

Now the car is back in my possession and I’m not sure what to do. We need to drive it a fairly long distance in a few weeks and I’d rather not do it with no AC. Does anyone have any idea what could be causing this issue?

One more piece of info: whenever the AC starts to weaken while driving it, all of a sudden the air coming through the vents becomes more humid and carries a damp smell. When that happens, you have about 5-10 minutes before the air ceases to be cold at all. Sometimes pulling over to turn the car off and on will revive it.

 

So this is a pure guess but my guess is that it's one of the temp sensors are bad and hot temps is causing it to send bad data. It might be the inside temp sensor but I know there is an outside temp sensor too.

My thinking with this is that over a certain temperature the sensor just doesn't work at all or is sending bad data so the computer is just shutting itself down.

The other thing it could be is the pressure sensor for the system is bad and it's shutting off because it's reading the pressure is too high.

 

Thank you, this definitely all seems plausible. I think the outside/ambient air temp sensor is okay because the reading of the outside temp displayed on the dash is accurate. But maybe I'm off the mark there.

Do you know if the inside temp sensor is the little slatted box beneath the ignition? Or is it the black dome near the passenger side windshield?

 

so a couple things, if it was low on refrigerant, then it leaked out from somewhere. Did the shop say the pressure was still correct when you took it in the second time? Or did he just look start looking for signs of where the dye leaked out? The outside air temp can effect the refrigerant pressure , sovif got low again, that might explain why the compressor started engaging after the car had been sitting. There is a cabin temp sensor in the dash by the drivers right knee. The lower section of the dash comes off pretty easily. The sensor can get full of crap, and keep it from working. So start there. In my car the compressor started making some crunchy noises, and as it got older the noise got worse, and it performed about the way your describing yours. I had to replace the compressor cause the clutch was worn out and stopped engaging when the temp was hottest and the refrigerant pressure would be its highest, so the compressor wasn't able to cycle correctly.
Check the dash semsor and get the refrigerant pressure checked again, please keep this thread updated to help the next guy with the same problem. Good luck

 

Thanks dwoods, I really appreciate the advice. I have an update: after taking out the cabin temp sensor, cleaning it, and putting it back in, the AC is now working. Because of the intermittent nature of my problem, I'm hesitant to believe its fully fixed. But it would be amazing if this ends up being what it needed. Here's a more detailed explanation of my process for cleaning the sensor:

Taking the lower section off of the dash is indeed pretty easy. I only had to remove these 2 screws and depress the 2 tabs on the left side and in the center of the cover.


I just let the cover hang down in the footwell with the light and ODBII port still plugged in. There was enough slack and room for my head for this to feel safe.

Once that was off, I had to remove the ignition cover to reveal 3 of the necessary bolts to fully remove the lower dash cover. I used a stiff butter knife with a thin rag around it. There are 2 clips on the top and 1 on the bottom. I had to be careful, but it came off pretty easily.


Once that was off, it was easy to see all the 10mm bolts I needed to remove in order to take the lower dash off completely (6 in total). The sensor was really easy to access after that, as its connected to the lower dash cover via 1 phillips screw. I unattached it from the cover and then gingerly removed the hose and wire harness.



Once I had the sensor out of the car, it was easy to see that it was indeed extremely dirty. I took a vacuum cleaner to it and then sprayed some D5 contact cleaner inside. Using a q-tip, I got all the debris out until the thermistor at the opening looked nice and shiny.




Now here's why I'm a little reticent to claim victory: After getting everything put back together, I started the car up and drove it around. It wasn't blowing hot but it definitely wasn't 65 degrees. I parked it back in the driveway and put the sun visor up. About 30 minutes later, I got back in the car to take it to the shop and get the refrigerant pressure checked again. Started it up - blowing cold. I drove it to the gas station to refuel - still cold. I drove it to the grocery store and parked it in the hot sun while I went inside - still cold. It's promising, but I guess time will tell. I'll make sure to update the thread when I know more. Thanks again

 

Let me know if you need additional info.