Confusing AC fault code repair/reset
Thread Starter
Zen Vet Master Level VII
Joined: Mar 2016
Posts: 5,218
Likes: 1,174
From: Southlake, TX
Confusing AC fault code repair/reset
My AC on my 91 is working intermittently.
When I run the diagnostic on the computer I get a "09" or low Freon reading. I had the system professionally checked and they said the pressure readings are all in specifications. The system has been 134 converted.
I follow the FSM and reset the system and the AC comes on as it should. It works immediately and I get about 42 degrees out the vent which I'm happy with. I can hear the compressor and/or the fan coming on/off which (I believe?) is normal. The system will work fine after the reset.
However after a couple of on/off cycles of the car, the system jumps back to fault mode and shows low Freon reading again. I know that if I reset the system it will go back to working.
Is there a possibility that an AC pressure switch is reading faulty? Is there a way to test them on the car or is it best to swap it out?
If I swap it out, does the whole system need to be evacuated and recharged or is this something that I can just replace by screwing in and out?
Or is it something different all together?
Thanks!
When I run the diagnostic on the computer I get a "09" or low Freon reading. I had the system professionally checked and they said the pressure readings are all in specifications. The system has been 134 converted.
I follow the FSM and reset the system and the AC comes on as it should. It works immediately and I get about 42 degrees out the vent which I'm happy with. I can hear the compressor and/or the fan coming on/off which (I believe?) is normal. The system will work fine after the reset.
However after a couple of on/off cycles of the car, the system jumps back to fault mode and shows low Freon reading again. I know that if I reset the system it will go back to working.
Is there a possibility that an AC pressure switch is reading faulty? Is there a way to test them on the car or is it best to swap it out?
If I swap it out, does the whole system need to be evacuated and recharged or is this something that I can just replace by screwing in and out?
Or is it something different all together?
Thanks!
Melting Slicks
Joined: Dec 2008
Posts: 2,772
Likes: 64
From: Mystic CT
R134 and r12 run at different pressures and need pressure switches set for the gas being run. The dealer switched mine to R134 without asking and caused a pile of problems and has never cooled as good as it used to. On top of that cost a pile of money that could have been avoided. He said swapped it because could not get R12. Sat down with service manager and told him to Google R12 and there was all the R12 a guy could ever need for around $50 a pound.
I believe the switches have a Schrader valve under them and can be easily change but check with FSM or real AC that does cars
I believe the switches have a Schrader valve under them and can be easily change but check with FSM or real AC that does cars
Thread Starter
Zen Vet Master Level VII
Joined: Mar 2016
Posts: 5,218
Likes: 1,174
From: Southlake, TX
It also makes sense that when doing the 134, they just filled it with freon and some PAG and sent her on the way.
My guess is that I need to get '96 model pressure sensors as that is 134 sensitive?
Melting Slicks
Joined: Dec 2008
Posts: 2,772
Likes: 64
From: Mystic CT
Thanks- this is what i was hoping for as that makes sense. I'll do a bit of checking on the valve.
It also makes sense that when doing the 134, they just filled it with freon and some PAG and sent her on the way.
My guess is that I need to get '96 model pressure sensors as that is 134 sensitive?
It also makes sense that when doing the 134, they just filled it with freon and some PAG and sent her on the way.
My guess is that I need to get '96 model pressure sensors as that is 134 sensitive?
Team Owner
Joined: Sep 2003
Posts: 25,393
Likes: 2,741
Thanks- this is what i was hoping for as that makes sense. I'll do a bit of checking on the valve.
It also makes sense that when doing the 134, they just filled it with freon and some PAG and sent her on the way.
My guess is that I need to get '96 model pressure sensors as that is 134 sensitive?
It also makes sense that when doing the 134, they just filled it with freon and some PAG and sent her on the way.
My guess is that I need to get '96 model pressure sensors as that is 134 sensitive?
https://www.corvetteforum.com/forums...ubleshoot.html
Thread Starter
Zen Vet Master Level VII
Joined: Mar 2016
Posts: 5,218
Likes: 1,174
From: Southlake, TX
It seems you've likely NOT returned the car to him for the diagnostics! Maybe it's time? Maybe a reason you've decided NOT to? Did you and he offeredd up no reasonable solution?
https://www.corvetteforum.com/forums...ubleshoot.html
https://www.corvetteforum.com/forums...ubleshoot.html
He said to loosen the adjustment screw 1/2 turn which should compensate for the difference between R12 and 134.
I offered to bring him the car and pay him for his time but he refused saying that it would take me less than 5 minutes. He said if I mess it up, to bring it to him and he would make the adjustment.
I'd say that was pretty fair and pretty honest.
Melting Slicks
Joined: Dec 2008
Posts: 2,772
Likes: 64
From: Mystic CT
Actually, I called him today (Ricky at AA Automotive Air in Haltom City, Texas) and he gave me a fix to try. I explained the situation and what I uncovered by myself and he told me to take the connector off the pressure gauge on the "fat" line and look deep in the connection socket for a small adjustment screw.
He said to loosen the adjustment screw 1/2 turn which should compensate for the difference between R12 and 134.
I offered to bring him the car and pay him for his time but he refused saying that it would take me less than 5 minutes. He said if I mess it up, to bring it to him and he would make the adjustment.
I'd say that was pretty fair and pretty honest.
He said to loosen the adjustment screw 1/2 turn which should compensate for the difference between R12 and 134.
I offered to bring him the car and pay him for his time but he refused saying that it would take me less than 5 minutes. He said if I mess it up, to bring it to him and he would make the adjustment.
I'd say that was pretty fair and pretty honest.
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Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
Gut Feeling
Yes the pressures are different between R12 and R134. But if you look at the charts there is not much difference but a few pounds at operating pressures. R12 pressure switch cutout is 25 and R134 is 22.5 psi. & most of these switches are not that accurate when new and do change over time somewhat not causing any noticeable effect to the driver.
Aside from technical icing, there is some leeway in these systems till they really stop working.
Don’t know if the orifice tube might have some affect on the symptom of the problem. But I think the pressure has to be really low before a genuine error code is generated.
I might look at the high pressure sensor (sensor in the high side) because this is where system pressure is actually measured by the ECM. It may be defective, just a suggestion.
Yes the pressures are different between R12 and R134. But if you look at the charts there is not much difference but a few pounds at operating pressures. R12 pressure switch cutout is 25 and R134 is 22.5 psi. & most of these switches are not that accurate when new and do change over time somewhat not causing any noticeable effect to the driver.
Aside from technical icing, there is some leeway in these systems till they really stop working.
Don’t know if the orifice tube might have some affect on the symptom of the problem. But I think the pressure has to be really low before a genuine error code is generated.
I might look at the high pressure sensor (sensor in the high side) because this is where system pressure is actually measured by the ECM. It may be defective, just a suggestion.
Thread Starter
Zen Vet Master Level VII
Joined: Mar 2016
Posts: 5,218
Likes: 1,174
From: Southlake, TX
So, I made my AC "repair" but it actually felt like an adjustment.
I took off the connector, put a flash light on the inside (it is super small) and saw the standard screw head. I gently dropped in my small screw driver and let it seat, then I spun it half a turn. It took all of 5 minutes (as told to me).
I started the car and the AC worked as before.
It seems the adjustment did not do any damage and I'll see over the next few days if this did the trick on a more permanent level. Gotta love a free fix!
I'll keep you posted!
I took off the connector, put a flash light on the inside (it is super small) and saw the standard screw head. I gently dropped in my small screw driver and let it seat, then I spun it half a turn. It took all of 5 minutes (as told to me).
I started the car and the AC worked as before.
It seems the adjustment did not do any damage and I'll see over the next few days if this did the trick on a more permanent level. Gotta love a free fix!
I'll keep you posted!
Thread Starter
Zen Vet Master Level VII
Joined: Mar 2016
Posts: 5,218
Likes: 1,174
From: Southlake, TX
Not sure yet, I made the adjustment, the AC worked but with TG going on I have not had a chance to run the car today. Tomorrow for sure and I'll post my results.
BTW... I picked up another regulator at Auto Zone to swap just in case this one (or my fix) does not work.
BTW... I picked up another regulator at Auto Zone to swap just in case this one (or my fix) does not work.