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A/C Problem Mechanic Can't Figure Out


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Hey all,

I wrote about a week or so ago about a code AO12 - Low Side Temperature Sensor that I was getting. When I ran diagnostics the code ran as an "open" so I disconnected the plug to the sensor, jumpered it, and the code reverted to a "short" - all of which points to a bad sensor.

Well, b/c the refrigerant has to be recovered and the system recharged I took it to a local mechanic that does pretty good work. He tested things and said that the system had twice the normal pressure and that he thought it was the filter or lines that needed cleaning instead of the sensor. He checked the filter and lines and said things were ok. He put air back into the system to test it...and here's where it gets weird.

He said the system (I guess the clutch/compressor) would kick on and off. It wouldn't stay on and when he tested it, the system had once again built up way too much pressure. He believes the sensor code is a symptom and didn't replace it. He can't figure out why the system would build pressure if the lines and filter are clear. He then referred me to other mechanics in town saying to let him know if and what someone else figures out. The good part is that he at least didn't charge me for anything b/c he couldn't fix it.

I changed the blower motor about 2 weeks before all of this started, but it worked fine after that. About 2 weeks later it would still blow air, but it wouldn't get cold. So that's where I'm at. Sorry for the long post, but does anyone have any ideas or suggestions before I take it to somebody I don't know or go to the dealer to pay top $$? What could be the problem? Thanks for any help or ideas.

Jonathan

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It sounds as though you've proved the low side temperature sensor bad. I'd like to have seen it replaced.

Further, if I understand correctly, you have high system pressure with the proper charge installed. That's a classic sign of a restriction. The most likely culprit is the orifice tube right next to the low side temperature sensor.

Until someone else chimes in, here is some A012 info from my 1995 FSM.

Text: http://i7.photobucket.com/albums/y299/WBucket/ACLow1.jpg (135KB)

Chart: http://i7.photobucket.com/albums/y299/WBucket/ACLow2.jpg (100KB)

Regards,

Warren

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There is no means of avoiding the final collapse of a boom brought about by credit expansion. The alternative is only whether the crisis should come sooner as the result of a voluntary abandonment of further credit expansion, or later as a final and total catastrophe of the currency system involved. - Ludwig von Mises

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Totally agree. High side High, low side low, plugged orfice. My only problem is why an AC mechanic can't see that.

BTW, what kind of contortionist do you need to be to change an orfice tube on this model?

Never underestimate the amount of a persons greed.

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Thanks...I have the manuals so that's how I came to the conclusions that I have. He didn't replace the sensor b/c he felt like it was a faulty code...that the system was saying the sensor is bad as a symptom of some other problem, most likely a restriction. At that time I didn't want to insist on replacing the sensor because, after all, he's the mechanic. :P He couldn't find a restriction, but I don't know if he checked the specific orifice tube you referred to.

I'll give the post another day or so to see who else concurs or offers any advice before I decide whether to give him another shot (I at least know him - that he's honest, has done good work before, and is fair in pricing) or take it to someone else. Thanks again for your input.

Jonathan

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Did he pull the orifice tube, or filter as you call it, and check to see if it was clogged? If it is, your in for a new compressor.

JonnhyG,

I believe the orifice tube is at the joint along the firewall on the passenger side. No contortions involved at all.

Kevin (KHE) is our resident A/C expert. See what he has to say when he chimes in.

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The test you did indicates that the sensor is bad (opened) - Since the system needs to be recovered anyway to replace the sensor, I would also check the orfice tube for any debris. It is in the line along the firewall.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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Here is a diagram of the AC system that should help (ignore the red circle)

post-2998-1147118839.jpg

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Did he pull the orifice tube, or filter as you call it, and check to see if it was clogged? If it is, your in for a new compressor.

A few lifetimes ago (car lifetimes, that is) I changed the orifice tube on my '83 Coupe D'Elegance. It got me through the remainder of the summer season. Barely. Yep, needed a compressor in the fall.

Regards,

Warren

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There is no means of avoiding the final collapse of a boom brought about by credit expansion. The alternative is only whether the crisis should come sooner as the result of a voluntary abandonment of further credit expansion, or later as a final and total catastrophe of the currency system involved. - Ludwig von Mises

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