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My AC was not working and when I ran a scan, I got an error from the high pressure switch (G65) saying "open or short to ground". So, off came the bumper to replace the switch. The switch was 8E0 859 126 and I replaced it with a Santech MT 1207 which says it is a replacement for that specific part number.
After clearing codes and starting the car back up, I still didn't have A/C and the compressor was not running. However, the error code had changed to the following:
I hooked up a can of Freon to the low side which showed no pressure. I was able to fill it so that the gauge showed in the green zone for full, but I'm concerned that without the compressor actually running that's not a credible indication.
So, if I can't figure it out I'm ok bringing to someone. However, I'm reluctant to put the front bumper back on if it might still be a high pressure switch issue (as in the replacement really isn't compatible).
The system is filled by weight, not by pressure, so you could have overfilled it. The only way to get the right amount in is to make sure the system is fully evacuated and add back in the necessary quantity. I'm not great with diagnosing the A/C system, so I can't be of much help beyond that.
If high pressure switch says lower limit exceeded per below, I would say it remains underfilled.
But I really would not fool around here with the can stuff, especially if you get beyond what seems like top up. "Seemed like a good idea at the time" can lead to blowing up the compressor and other bad outcomes if meaningfully overfilled. Getting compressor replaced on these labor wise is not fun, let alone $$.
FWIW, on my D3 W12, it finally pooped out on AC something like 7-8 years in. I owned it from one year old CPO so knew the whole history. The dealer evacuated it and refilled as mine tired and got more and more erratic, telling me its filled quantity had fallen to slightly under half the prescribed weight. They figure that out when they evacuate it. With green regs and such, modern AC systems are also designed for far less refrigerant than in the "old days," even if it is not the most destructive freon of yore. But that also means there is less tolerance for loss percentage wise. Obviously by half full or less, it could no longer work at all effectively. Dealer identified no leaks on mine and all was well once again post service.
BTW, realize the compressor does not have a conventional clutch if you are listening for that as an indicator whether it is "on" or not. It is still filled conventionally though from low pressure side with system running.
My net from that experience is almost to expect by the age these cars are now that it is likely to need a shop re do on the refrigerant refill, and it needs to be weighed to get it right. Some similar posts some years ago from various other hands on owners when mine was faltering reinforced that same conclusion--both that it loses refrigerant over time and then likely needs some attention by 7-10 years in.
+1. My system performance had been marginal at best in the TX heat from the day I bought it. And got to the point I was really soured on driving it in the summer and ready to sell her on. As a last effort, I went back to my buddy's shop and did a full purge, vac, and PRECISELY weighed recharge. Now its the best AC on any vehicle I've owned. Even at an ambient air temp of 105, I am cool and comfortable within 1 mile of leaving my office.
Evac and charge by weight...exact weight per the sticker under the hood...is the only way to do it right.
Thanks a lot for the feedback. I think the sensor is fixed and am going to button things up. Then it's off to a pro to do a full evac/purge and then refill it properly. Will let you know.
Hey everyone - it's fixed. The sensor was not only bad, but I believe leaking as well. Got it replaced and had a shop evacuate the A/C and refill it with the right weight. Everything working and error codes gone. Thanks for the help.
04-26-2017, 04:37 PM
A/C problem - G65
