The imfamous B1347 very low refigerant warning is back

[greg-sls]

I got this error code again and it shuts down the compressor. Thanks to all who directed me on to how to "reset" this error on the dash - it makes it much easier than disconnecting the battery. Anyway, I again checked the pressure at the low port side after a reset, and it is just fine (45 psi). I searched older threads and found that others have had this problem before too - a false or bad read from the sensor just after the evap coil near the firewall.

My question is this: Is the sensor "normally open" or "normally closed" for a good read? Also, if my sensor is going bad, do I need to evacuate the system to change it out? (97 SLS)

PS - I disconnected and reconnected the clip to it to be sure it has a good electrical contact to the sensor.

[Ranger]

I wouldn't swear to it, but I think the sensor is normally closed.

Yes. I believe you have to evacuate the system to R & R it.

[greg-sls]

Thanks Ranger - that would be helpful if I had to do a change-out. It would also allow me to "test" for a bad sensor by "jumpering" the clip to see if the error stays off. I don't like to do that in case a real drop in pressure should occur, but doing that for a week or so, it would confirm if it was a bad sensor.
I hope I'm making the right assumption that the sensor on the low side (larger aluminum tubing) would be the culprit for this error code.

[Ranger]

Yeah, that's the low pressure sensor.

[CadillacSTS2003]

are you sure its not in fact really air pressure and that it is infact low?

[greg-sls]

CadillacSTS2003, I couldn't be sure about that...I think the low pressure sensor just measures a threshold PSI, and if it's below a certain level, the sensor "opens" the circuit and thus the error is reported to the ACM. Once that happens, the compressor shuts down and the messages appear on the DIC. What would surprise me is if the sensor could actually "detect" the absence or presence of freon vs just line pressure. So is that a possibility?