AC code 09
Thread Starter
Racer
Joined: Sep 2017
Posts: 452
Likes: 55
From: Marianna Fl
AC code 09
Working on a 1990 coupe with C68 system.
I have been getting a seemingly random HVAC code 09 this summer. Last year I converted over to R134A and the system worked great all year. 3 times so far I have been out with the wife and the AC cuts out with a flashing indicator. Check the code and its always 09. I test the off pressure and its about 140psi both sides. When running I see about 225psi and 35psi with the compressor running. I have tested the high and low pressure cut off switches and both are working fine. The system works like usual most of the time and only takes a reset by pulling the ctsy fuse or the battery. I am wondering if it is from the high temps because its Florida and someone forgot to tell it we are in fall now, or if I have a bad pressure sensor. I can not read the digital sensor so I'm not sure if it is falling out of its limits. Any suggestions would be appreciated, also I cant find a part number for the digital sensor or if you have to recharge the system when you replace it.
I have been getting a seemingly random HVAC code 09 this summer. Last year I converted over to R134A and the system worked great all year. 3 times so far I have been out with the wife and the AC cuts out with a flashing indicator. Check the code and its always 09. I test the off pressure and its about 140psi both sides. When running I see about 225psi and 35psi with the compressor running. I have tested the high and low pressure cut off switches and both are working fine. The system works like usual most of the time and only takes a reset by pulling the ctsy fuse or the battery. I am wondering if it is from the high temps because its Florida and someone forgot to tell it we are in fall now, or if I have a bad pressure sensor. I can not read the digital sensor so I'm not sure if it is falling out of its limits. Any suggestions would be appreciated, also I cant find a part number for the digital sensor or if you have to recharge the system when you replace it.
Le Mans Master
Joined: Jan 2006
Posts: 5,620
Likes: 206
From: Orlando FL
The 09 error code is a low Freon error as you know. But the programmer is not measuring pressure, it's measuring cycling time. If the cycles are too short and it cycles to many times in a minute it will then throw the code.
AC systems operate much different while driving compared to standing still in the driveway. Most of the time on the driveway fan speeds are set to high which translates to longer cycling times or possible none at all depending on RPM, Freon charge and ambient temperature.
When driving, after the car is cooled down, fans are usually on low fan speed and you have a lot more air being pushed thru the condenser. All of this relates to shorter cycling times which may cause a code to appear.
You also need to check what pressure the cycling switch opens. Should be around 22.5 psi for R134. (Put fan on low speed to check). If the switch is to high, it may cause to much cycling. Also if you converted from R12, the cycling switch that screws on the evaporator is for R12. You can't screw on a 134 switch because the threads are different. Many of the R12 cycling switches are adjustable with a screw. It could be out of adjustment or possibly defective. There are also YouTube videos on how to adjust the cycling switches.
AC systems operate much different while driving compared to standing still in the driveway. Most of the time on the driveway fan speeds are set to high which translates to longer cycling times or possible none at all depending on RPM, Freon charge and ambient temperature.
When driving, after the car is cooled down, fans are usually on low fan speed and you have a lot more air being pushed thru the condenser. All of this relates to shorter cycling times which may cause a code to appear.
You also need to check what pressure the cycling switch opens. Should be around 22.5 psi for R134. (Put fan on low speed to check). If the switch is to high, it may cause to much cycling. Also if you converted from R12, the cycling switch that screws on the evaporator is for R12. You can't screw on a 134 switch because the threads are different. Many of the R12 cycling switches are adjustable with a screw. It could be out of adjustment or possibly defective. There are also YouTube videos on how to adjust the cycling switches.
Last edited by pcolt94; Oct 2, 2019 at 10:12 AM.
