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R134 & A/C Service Light, 91 Reatta

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I have only owned the 91 Reatta for two weeks but at freeway speeds with A/C on the system shuts down & A/C service yellow light comes on. Removing the + battery cable resets the A/C service light. After a reconnect of cable, this allows me to use the system at neighborhood speeds. This has probably been covered before but does anyone have any ideas?? (System has been checked by mechanic and good pressure and quantity of R134).

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Since you did not list what was changed when you converted your R12 system to R134a, the technician probably did not take into account the fact that the computer on a Reatta monitors the A/C system, including the freon pressure. This is a feature found on very few cars, the Reatta being one of them. <P>Your system operates at a higher pressure on R-134a than it did on R12. For example, the high pressure side of the compressor probably ran at 225-275 PSI under high temperature conditions. An R134a system might operate as high as 325-425 PSI, and would be considered normal. <P>Because of that, the pressure sensor is reading a pressure that is too high. If your R12 system operated at that pressure, it would probably mean the fan wasn't working and excess heat was building up in the system. The light and loss of cooling is probably due to the BCM (Body Control Module) reading the high pressure as a failed system, and it cuts the A/C compressor clutch current off to prevent damage to the system. Disconnecting the power clears the code out of the computer until it happens again. <P>Best bet is to talk to a knowledgable A/C tech and see if he can modify the system to not read the high pressure as an error. This may mean having the computer reprogrammed, or 'flashed' with updated programming or other modifications. Make sure you go to someone who is knowledgable about GM/Fridgidaire systems or has a Mitchell computer system. Either way, they will know if there is a program they can load into your car's computer.<P>DO NOT experiment with this yourself if you don't know what you are doing. Fooling around with a system that operates under this kind of pressure is dangerous to you, and could get expensive if you damage a system component.<P>Good luck!

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I have a 91 too, and I noticed a similar problem when I lived in Maryland. I now live in SC and I rarely, if ever see it any more. What happened to me, was on cold days, I would see the indicator CHECK AC. I had my freon changed out twice while I lived in MD, and it was because I got the CHECK AC light each time winter or fall approached. The third straight fall, it happened again, and this time, I was pretty hacked off. While I was driving, I began to fiddle with the controls. I had nothing to lose.<BR>I turned my thermostat down as far as it would go, and put my AC on, and the problem went away. I've been doing that ever since. I'm not sure what I did by doing that (technically), but it did clear the problem each time. Now that I live in SC, it rarely gets cold enough for the situation to present itself like it did in MD. Incidentally, I've lived in SC now going on two years, and I haven't changed my freon in about 3 years now. I probably didn't need to change it the two times I did, but I did it because I saw the indicator. So...don't take those indicators too literally before you have tried about everything possible with the controls you have.<BR>Hope this helps.<BR>Jim Houston<BR>Charleston, SC

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