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HVAC Anomaly


Rich

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I had this issue twice in the past six weeks with my 1997 Eldorado, both times on rather hot sunny days. While driving with the A/C on, the cold air stopped coming out of the A/C vents. As you can imagine, with the hot outside temp and the sunload, the cabin became quite hot within a minute or so. I fiddled with the HVAC controls and the problem corrected itself. Notably, when the cold air stopped coming from the vents, cold air was still being produced as I could feel a slight cold airflow from the side of the console where the carpeting is loose. The compressor was replaced three years ago and the blend door actuator was replaced about four years ago. Just as a test, I just set the temperature to 60 and the A/C works fine. I then set it to the highest setting (90?) and immediately got heat. Seems to be fine now. The only codes that are set are: PCM P0325H; ACM B1313H; PZM B0533H; PZM B1971H; PZM B1983H. The only one that seems to have any relevance is the B1313 fault code, but I'm not really sure. As I said, the problem seems to have corrected itself and all the codes are "History" codes. Has anyone else experienced similar events? BTW, the Eldorado has about 135,000 miles, all of which were put on by me. As always, thanks for your opinions and advice.

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P0325 PCM Knock Sensor Circuit
B1313 High Side Temp Sensor Short Circuit
B0533 Fuel Sensor Open/Shorted To B+
P0533 Air Conditioning (A/C) Refrigerant Pressure Sensor Circuit High Voltage
B1971 Inadvertent Power
B1983 Device Power Circuit Low

This is a pretty motley crew of codes. I added P0533 because I couldn't see the point of B0533 unless the fuel guage was glitching too, which you didn't mention, and P0533 looks a lot like B0533 on the DIC and that code *is* related to the A/C.

The B1983 code is a power seat code.

All of them look like wiring harness problems. I would think fuse except that all of them are HISTORY codes. The B1313 seems like a short circuit, but all the rest look like they can be caused by loose terminals in the connectors, or loose or dirty connectors. Short circuits are usually caused by something crushing part of the wiring harness and cutting through some insulation, which should be easy to find.

I suggest a thorough cleaning and inspection of the wiring followed by clearing the codes. You can run the codes while the problem is happening for areal picture of what is going on, and you can look for codes that come back anytime.

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-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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The high side temp. sensor short circuit sometimes will set due to a damaged sensor because someone installed the orifice tube backward, Is the code current or history?

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

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If no work was done on the A/C unit recently, my money would be on a plugged (restricted) orifice tube or screen.

Never underestimate the amount of a persons greed.

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If there was moisture in the system, it could freeze in the orifice tube - that would stop the cooling until the system warmed up enough to thaw the blockage. It wouldn't explain the shorted sensor code.

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

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All of the codes are "History", not current. What exactly is an orifice tube and where is it located? Is this the likely cause of the blockage of cold air flow through the A/C vents? What might cause the blockage and how involved is it to clear? Jim, I'm pretty sure the code was "B" 0533, not "P" 0533 but I will double check tomorrow. Is the wiring harness easy to access?

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All of the codes are "History", not current. What exactly is an orifice tube and where is it located? Is this the likely cause of the blockage of cold air flow through the A/C vents? What might cause the blockage and how involved is it to clear? Jim, I'm pretty sure the code was "B" 0533, not "P" 0533 but I will double check tomorrow. Is the wiring harness easy to access?

If it is a history code, I wouldn't worry too much about it yet. The orifice tube is an expansion device in the high pressure refrigerant line. The high pressure refrigerant passes through the orifice, expands, and cools, then it enters the evaporator where it cools the air for the cabin. It wouldn't be the direct cause of the blockage of the air through the vents.

If the evaporator freezes, that would block the airflow. It is possible that the actuator was off calibration and when you cycled it to 60 and then 90, it brought it back into calibration and fixed the problem.

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

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I ran the codes again this morning. Same results as yesterday. The 0533 code was definitely a "B" code, not a "P" code and all are still History, none Current. Everything is operating as it should so I'll just consider the events as aomalies for now. Thanks guys.

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Did you notice the fuel gauge glitch out when the problem happened?

These are all unrelated codes. Perhaps something momentarily shorted out things. I would reset all the codes and see which ones come back.

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-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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I didn't think to check the fuel gauge when the A/C glitched but will make it a point to do so if it happens again. The fuel gauge is presently working fine though. I thought the codes cleared themselves after a certain number of driving cycles. How would I clear them manually?

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When you read the codes from the DIC, the parade of codes ends with the prompt "PCM?" When you see that, press Fan Up (Yes), then Fan Down until you see "RESET CODES?" then Fan Up. Press OFF to back out to go to the next module. The modules will be in this order: PCM, IPC, ACM, SDM, TCS, RSS, PZM, IRC, RFA, CCP, MSM, MMM, and PHN (if you have a car phone or OnStar). Press Fan Down to skip a module, Fan Up to enter a module, Fan Down to skip options until you come to "RESET CODES?" in each module that threw a code, Fan Up to reply YES to the "RESET CODES?" prompt, and OFF to back out to the previous level. When in doubt about what you see, press OFF to back out of whatever is happening.

When you are done, press OFF a couple of times to read the codes again. If you see any that you haven't reset, press Fan Down to scroll to that module and clear its codes.

When you are done, press AUTO (the Temperature knob pushes in), INFO RESET, or turn off the key.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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  • 1 month later...

The A/C glitch occurred again this morning. I couldn't immediately check for codes as it happened on the parkway at speed. I was able to check the codes about ten minutes later and saw only two: PZM B 0533H and MMM B 2144H. The first indicates fuel sensor open, the second has to do with the D/S mirror, and both are History codes. Nothing HVAC related. As per the board's suggestion, I checked my fuel gauge during the issue which appeared to be fine, or reasonably accurate when compared with the DIC "Fuel Used" readout, although over the past few weeks, I did notice that the fuel gauge does vary in its accuracy. It sometimes will read accurately showing perhaps 3/4 of a tank, and then while driving will gradually creep forward to inaccurately reading almost full. It will then reset upon shutdown and startup and read fine. Hardly a huge problem but just mentioning it for additional information. Is it odd that the HVAC issue isn't setting a code?

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  • 5 months later...

Throughout the winter I've been fiddling with the HVAC controls redirecting the heat to come out of the A/C vents rather than from the floor vents where the standard AUTO setting would normally direct most of the hot air . I was trying to replicate the fault that manifested itself last summer with the air conditioning. Never did the hot air coming from the A/C vents redirect itself as it did with the air conditioning last summer. I sort of expected the issue to continue through the winter with hot air if the actuator was at fault. Does this sound odd?

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Not really. It was (is?) probably a sticking mix door or a vacuum leak, and those sometimes come and go. And, your codes look like an intermittent electrical problem, and intermittent problems sometimes don't show up for a long time. Stay with it, and we will look for it again when (if?) it shows up.

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-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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  • 1 month later...

Well, today was a nice warm sunny day. Was driving around and after a few hours the A/C stopped coming out of the A/C vents. I was approaching a traffic light at the time and was rolling along at perhaps 10 MPH off throttle. The temp was set to 68 degrees at the time. When the problem occurred, the HVAC panel still indicated that air flow was coming from the footwell area and the main A/C vents, even though there was no air flow from the upper vents. Not once did this issue arise over the winter with warm or hot air. It only seems to happen with cool or cold air. Very strange. I sure hope this isn't some random electrical glitch, or some impossible to find vacuum leak.

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This sounds like a stuck air door, or a vacuum line off the A/C controller. Read the codes and see what's up.

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-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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I cleared the codes a while ago and this morning the following codes were set:

PZM B 0533H Fuel Sensor Open/Shorted To B+

PZM B 1552H Keep Alive Memory (KAM) Error

PZM B 1558H BCM EPROM Checksum Error

PZM B 1983H Device Power Circuit Low

MMM B2144H Left Front Mirror Vertical Position Sensor Circuit Low (Haven't yet replaced the mirror)

These are the same codes that keep setting, fortunately all are "History codes". Not sure if any relate to HVAC functions. I had the blend door (actuator door) replaced twice, once on July 2, 2009 at 109,009 miles and once on September 27, 2010 at 123,255 miles. The car now has approx 136, 500 miles. Engine vacuum doesn't appear to be the issue as the problem has occurred at both low and high engine vacuum. Maybe the problem is electrical? Where is the wiring harness and is it easily accessible?

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None of the codes relates to the HVAC. I find B1558 a bit ominous, although the History rating means that it's not a bad PZM. MMM and MSM codes can be set if a button is stuck or the movement is against the stops that limit how far a mirror (or seat) can move. If the mirror isn't moved against the stops, then it may be a bad sensor inside the mirror.

According to the FSM page 8C1-37, the B1983 code can be set by low battery voltage in "Cell 4." That's the Retained Accessory Power (RAP) as passed to the instrument cluster through the 20 Amp CLUSTER FUSE in the trunk compartment fuse block. There's not much on that except the steering wheel controls and the IPC.

You may have a low battery or a bad battery cable connection that drops your battery voltage too low when starting the car. You might clean the cables and put the battery on a trickle charger for awhile, clear the codes, and see what comes back with a known good battery.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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Thanks for the tips Jim. Regarding the mirror, my D/S outside mirror is permanently fogged. I already have another which I purchased on ebay that I need to have installed. Regarding the 1983 code, I had a new battery installed last November, 1,400 miles ago so I don't think it's the battery. That code was also set when I started this thread last July, four months prior to replacing the battery. I suppose this is beginning to look like a phantom electrical glitch.

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If you are getting B1983 every once and awhile, you may have a cracked fuse or corrosion in the fuse socket. All these things are simple and obvious... once you find them.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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  • 3 weeks later...

I think I found the problem. The main vacuum line runs from under the motor beauty cover on the passenger side to a check valve, then to a "T" fitting by the fire wall on the passenger side of the car. From the "T", one side runs through the firewall providing cabin vacuum, then toward the front of the car to the accumulator tank under the battery tray. One eight inch section of the vacuum line between the check valve and the "T" was completely degraded. When I handled it, it started to crumble. It was obviously still maintaining some vacuum, but its integrity was severely compromised. The part is no longer available from the dealer, so I replaced it yesterday with vacuum line I purchased at Autozone for $1.29, perhaps the cheapest fix in the car's history, if in fact this corrects the problem. I drove the car through a very varied driving cycle today with no issues. The HVAC didn't miss a beat. We'll see in time whether that small section of bad line was the culprit.

Regarding the fact that I didn't have this problem all winter, my thought is now that the cold weather caused the degraded line to contract, perhaps lessening the porosity of the line and allowing sufficient vacuum to maintain the correct baffle selection in the cabin actuator. When the warm weather returned, the line expanded with the heat and the vacuum was again compromised. Just a theory. I'll keep you all apprised of any relevant developments. Thanks again to all.

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  • 4 weeks later...

Well, I didn't find the problem after all. The issue continued to arise from time to time. I went on to replace every soft piece of vacuum line I could put my hands on, even those that looked fine. I also replaced the HVAC check valve with a new A/C delco repacement. Still having the issue. If the problem lies somewhere behind the dashboard, I don't know what I can do. I certainly can't pull the dash off, and I can't ask the dealer to fix the problem as they will replace every part they can until tey find the problem. I can't afford that method of repair. I wish there was an automotive HVAC specialty shop that had an expertise in auto A/C but I'm not aware of any. Totally frustrated. Don't know where to go from here.

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It has been a long time... Would you post the problem you're having as well as what you've done to attempt to correct the problem? That would help the members of this board to try to offer a solution to the problem.

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

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