Intermittent AC failure
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From: FL
Intermittent AC failure
AC has worked fine all along until...
I'm in South Florida. A few days ago it was well into the high 90s outside. I made a couple trips and had AC set to Low and it worked fine. Then midafternoon after it sat for about an hour I started the car and NO cooling whatsoever. Blower was strong but zero hint of cooling. I drove about 20 minutes to get home like that. My shirt was soaked.
(Dual was on; the passenger side was set to 75. I expect Dual had been on for months and the temp setting on the passenger side hadn’t been changed for months.)
After about an hour or two I started it up again and it worked fine. I took it directly to my mechanic (excellent mechanic and electric expert who is almost always in the shop working). Freon was fine. Scan looked fine. We replaced the "regulator" in the fuse box on the spot just out of prudence since it’s easy.
He told me the next time it happens I should leave it running, pop the hood, and see if the fan is blowing and the compressor shaft is turning.
It continued working fine the rest of the day and evening.
The next day, I started it up mid-afternoon for the first time that day (it was cloudy and not in the high 90s like the previous time) and again it blew hot air with ZERO hint of cooling. I drove about a quarter mile like that and, now certain it was in total failure again, I pulled over, left it running, popped the hood, and checked to see if the fan was running and the compressor shaft was turning. Both of them were apparently operating fine. I got curious and I raced back to the cabin to see if it was still blowing hot air and sure enough now it was blowing cold air!
I've had the car for 14 years. I know how it behaves. This was not just a normal delay in reaching an operating temperature to enable it to start blowing cold. It was in total failure during that first quarter-mile drive until I stopped and got out to check under the hood. Then it was functioning properly when I got back to the cabin a moment later.
I drove it on a couple errands and it continued to cool fine. Then I went to the mechanic again. All looked fine again -- freon, scan, fan, compressor turning. It kept blowing cold after turning the car off and on multiple times (and I turned off Dual so both sides would be set to the same temp).
The mechanic expressed how challenging it is to nail down something as intermittent as this, especially when it hasn't acted up while at his shop He looked up common causes but it was of course vague. He said it could be the flow controller (?),.. or ambient temperature sensor... or the magnet in the pulley that engages the compressor... or the compressor itself...
He said there is nothing else worth trying to replace without more information. He said the next thing to randomly replace would be the sensor at the bottom front of the compressor (ambient temp sensor??), or the flow controller (??), but both require dumping the freon and the total cost would be well into the hundreds of dollars and it could very well be in vain anyway.
He said all I can do is wait for it to happen a few more times, and then we'll run a scan again and hope something has registered.
It worked fine the next day also through a few trips. That was yesterday. I didn’t drive it today.
Any suggestions on what to try next that might be worth the money? (I don't have money to throw away but I don't want to have the same issue at an inopportune time like when I'm headed to a meeting or have an associate or lady friend with me, and unless something triggers a report in a scan it would still leave me at risk of it recurring again and again.)
Thanks so much!
I'm in South Florida. A few days ago it was well into the high 90s outside. I made a couple trips and had AC set to Low and it worked fine. Then midafternoon after it sat for about an hour I started the car and NO cooling whatsoever. Blower was strong but zero hint of cooling. I drove about 20 minutes to get home like that. My shirt was soaked.
(Dual was on; the passenger side was set to 75. I expect Dual had been on for months and the temp setting on the passenger side hadn’t been changed for months.)
After about an hour or two I started it up again and it worked fine. I took it directly to my mechanic (excellent mechanic and electric expert who is almost always in the shop working). Freon was fine. Scan looked fine. We replaced the "regulator" in the fuse box on the spot just out of prudence since it’s easy.
He told me the next time it happens I should leave it running, pop the hood, and see if the fan is blowing and the compressor shaft is turning.
It continued working fine the rest of the day and evening.
The next day, I started it up mid-afternoon for the first time that day (it was cloudy and not in the high 90s like the previous time) and again it blew hot air with ZERO hint of cooling. I drove about a quarter mile like that and, now certain it was in total failure again, I pulled over, left it running, popped the hood, and checked to see if the fan was running and the compressor shaft was turning. Both of them were apparently operating fine. I got curious and I raced back to the cabin to see if it was still blowing hot air and sure enough now it was blowing cold air!
I've had the car for 14 years. I know how it behaves. This was not just a normal delay in reaching an operating temperature to enable it to start blowing cold. It was in total failure during that first quarter-mile drive until I stopped and got out to check under the hood. Then it was functioning properly when I got back to the cabin a moment later.
I drove it on a couple errands and it continued to cool fine. Then I went to the mechanic again. All looked fine again -- freon, scan, fan, compressor turning. It kept blowing cold after turning the car off and on multiple times (and I turned off Dual so both sides would be set to the same temp).
The mechanic expressed how challenging it is to nail down something as intermittent as this, especially when it hasn't acted up while at his shop He looked up common causes but it was of course vague. He said it could be the flow controller (?),.. or ambient temperature sensor... or the magnet in the pulley that engages the compressor... or the compressor itself...
He said there is nothing else worth trying to replace without more information. He said the next thing to randomly replace would be the sensor at the bottom front of the compressor (ambient temp sensor??), or the flow controller (??), but both require dumping the freon and the total cost would be well into the hundreds of dollars and it could very well be in vain anyway.
He said all I can do is wait for it to happen a few more times, and then we'll run a scan again and hope something has registered.
It worked fine the next day also through a few trips. That was yesterday. I didn’t drive it today.
Any suggestions on what to try next that might be worth the money? (I don't have money to throw away but I don't want to have the same issue at an inopportune time like when I'm headed to a meeting or have an associate or lady friend with me, and unless something triggers a report in a scan it would still leave me at risk of it recurring again and again.)
Thanks so much!
Last edited by Silverman1; Aug 9, 2025 at 09:54 PM.
CL Community Team
Joined: May 2005
Posts: 7,136
Likes: 1,706
From: VA
It may be the infamous flow sensor on the compressor which loses its magnetism over time but it can be corrected by sticking a cheap magnet on it. This link explains everything.
The flow sensor attaches to the compressor. It is a separate part and is very difficult to remove and replace with the compressor in the vehicle.
As explained in the link below that discusses how to try the cheap magnet trick to get the flow sensor to turn on the compressor.
Around post 174 is a photo and explanation of where to put the magnet etc. also posts 142 & 114-119.
Someone claimed that after a thousand miles the magnet re-magnetized the sensor and it worked without the magnet.
https://www.clublexus.com/forums/rx-...lution-12.htm
The flow sensor attaches to the compressor. It is a separate part and is very difficult to remove and replace with the compressor in the vehicle.
As explained in the link below that discusses how to try the cheap magnet trick to get the flow sensor to turn on the compressor.
Around post 174 is a photo and explanation of where to put the magnet etc. also posts 142 & 114-119.
Someone claimed that after a thousand miles the magnet re-magnetized the sensor and it worked without the magnet.
https://www.clublexus.com/forums/rx-...lution-12.htm
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Klaus
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Sep 18, 2010 07:38 AM
