2001 lincoln LS V8 Code # 1299

[rhanson1]

If anyone knows how I can get my hands on an automatic climate control wiring diagram, that would really help to expedite my troubleshooting and pinpoint the problem. Half the problem I'm having in finding a solution is that I don't really understand exactly how the system is supposed to operate.

[shorod]

The car I was working on was my wife's 2002. There were 3 identical sensors on the driver's side and one on the passenger side. I no longer have my 2004, so I can't see if there were two or four sensors on it. That also has me wondering if the same part number is used for her 2002 as would be in your 2004.

If you send me a private message with your e-mail address, I should be able to provide you with the wiring diagram for the system.

-Rod

[shorod]

I took a look at the manual and there should be at least two sensor on the driver's side, the Evap discharge sensor and the driver's discharge temp sensor. Both are under the dash, mounted to the center plenum. They would appear to be within inches of each other. On the passenger's side there is one sensor, the passenger air discharge temp sensor. The driver and passenger sensors are probably mounted after the evap sensor in the air flow to sense the air temp coming from the vents. Unfortunately I knew the sensor I replaced was bad so I didn't save the part or the box to avoid the possibility of using it at a later date not knowing if it was good or bad.

There's also a 4th sensor mounted near the ignition key cylinder switch which is the cabin temperature sensor.

-Rod

Originally Posted by rhanson1

Rod, I finally found two of the temperature sensors - the evaporator discharge temperature sensor on the driver's side, and the passenger heater core discharge temperature sensor on the passenger side. I know exactly what each one is because of the DTC's that are thrown out when I disconnect them. What was throwing me off in your previous instructions on how to access them was the removal of a knee panel. On my 2004 LS there are no knee panels in the footwells - it's all open when you stick your head underneath (a cost-saving change, no doubt).

I cannot find the driver heater core discharge temperature sensor. In a previous post, you said it was on the driver's side of the center air plenum near the evaporator discharge temperature sensor. Do you recall if it was upstream or downsteam of that sensor or how far away? I've poked my head around up inside there with a mirror, and I can only see the one sensor.

[rhanson1]

By sticking my head under the dash on the drivers side, I can see pretty much that entire side of the center plenum. The only temperature sensor that is visible is the evaporator discharge temperature sensor. If there's a heater core temperature sensor in the vicinity, then it must either be on a different side of the plenum that I can't see, or it's buried someplace inside a device housing. There is an actuator right near the evaporator discharge temperature sensor, and there's a plastic housing next to the actuator. I assume that the housing is for some kind of door operating assembly (perhaps the blender door?), and perhaps there's also a heat temperature sensor inside there too. I just don't know how the system components are laid out.

The more I think about this, the more I am inclined to discount the likelihood of a temperature sensor problem anyhow. It seems inconsistent with my symptoms. The temperature sensor is simply a resister - either it works or it doesn't. If I had a bad temperature sensor, that would not explain why my system works perfectly for a while. If there were a bad connection to the temperature sensor, that would explain erratic behavior, but my problem is not really erratic. To the contrary, it's actually quite predictable. After the engine has run for 15 minutes or so, the outlet air temperature begins getting progressively cooler. If I move the temperature setting up, the air will warm a little for a few minutes before turning cooler again. That procedure continues until finally I've got the temperature setting pushed up to 85, and all the outlets are blowing 50 degree air. When I push the temperature setting to 90, then I get all kinds of heat out of every outlet.

So I'm thinking that the symptoms suggest a problem with the heat blender door position. It seems that the heat blender door is positioned properly for the first 15 minutes or so that the engine runs, but then it gradually starts to close. I know that my heater cores are getting plenty of heat because the coolant pipes that connect them are very hot. And I know that the blender door isn't sticking or operative because they always open fine if I push the temperature setting up to 90.

So then I have to ask what is causing the heat blender door to mysteriously close up after a while? Again, I don't really understand what controls the door, but I assume it's an actuater that receives a signal from the ATC module. Therefore, I'm suspecting that my ATC module may be bad. The fact that the display of the ATC module has always become quite hot after a long trip also makes me suspicious. No one on this forum has indicated whether or not that is normal.

Normally, the only purpose of the evaporator discharge temperature sensor in any air conditioning system is to shut off the compressor before the evaporator coil becomes so cold that it ices up. So I doubt that's my problem here. I also doubt that I have a heater core temperature sensor problem because both the driver and passenger sides behave identically. That would mean that both heater core temperature sensors would always have to become faulty at the same time to produce the symptoms that I'm getting, and that seems unlikely.

I am assuming that there is only one heat blender door. If you tell me that there are two separate heat blender doors for the driver and passenger sides, then that complicates things. I wish I could figure out some way to determine the position of the heat blender door when I'm having this problem before I go buy another ATC module, but I can't. Perhaps a bad actuator could cause the blender door to behave this way too, although I'm not really sure how. I'm not quite sure where I'll go from here.

[shorod]

I think you're beginning to understand why the dealership didn't offer much help. Just think if you were paying them for all their time diagnosing this. Of course their scan tool would allow them to monitor the various actuator positions and temp sensor readings, which is how I was able to zero in on the evap temp sensor on my wife's car.

I think at this point you're left with either shotgunning parts, or finding a scan tool that can access the HVAC components in data stream mode and seeing what happens when working versus not working.

-Rod

[rhanson1]

I think the answer is the scan tool and, assuming that the dealer has one, I think I'll take the car back to the dealer. I know a lot more about this problem now than I did when I first took the car in for this problem before. If you were able to use a scan tool to zero in on a faulty evap temp sensor on your wife's car, I don't understand why the dealer can't diagnose exactly what the problem is with mine. Their mechanic's comment to me about having to tear the dashboard apart to figure out the problem makes no sense. Perhaps I'll simply ask the dealer to assign another mechanic to it - or take it to another dealer. Is there such a thing as a special mechanic certification for climate control systems? If so,then I'll ask for someone who has it.

[shorod]

I'm not aware of any special certification for this type of diagnosis. With the scan tool, they may need to be able to record the various datastream parameters when everythings working properly, then again when it's acting up, and compare the two. That might be the hard part, getting them to drive it long enough to get it to act up. Be sure they clearly understand the symptoms so they know when it's working find versus when it is experiencing the issues.

-Rod

[rhanson1]

That shouldn't be difficult. In fact, they don't even need to drive it. All they need to do is start it up when its cold and then take some readings when the engine first warms up. Then simply let it run in the parking lot for a half-hour and take some more readings. They will then have readings when the system is working fine vs. when its blowing cold air. This is not a situation where the problem is difficult to duplicate.

So, in case I just get blank stares when I suggest that they take some "readings", can you tell me exactly what that means? What are "datastream parameters" and how does the scan work? Is this a procedure that any dealer mechanic should be capable of doing?

[shorod]

I'm not a mechanic, and I was capable of doing it with my aftermarket scan tool.

I'm not fully familiar with the WDS or NGS tester that the dealership would use, but suspect it's conceptually similar to my OTC Genisys scan tool. With my tool, I connect it to the regular OBD-II diagnostic port under the driver's side dash. I then enter the appropriate information for the car and enter the "Climate Control" system. Once in that section, I have the option of checking diagnostic codes, gathering system information, going into the RepairTrac database, entering the datastream, or entering a customer datastream.

I would select "Datastream." This will display A LOT of real time readings of the various sensors, including the various temperature sensors, engine speed, battery voltage, the various climate control door positions, the temperature set point, DCCV duty cycle, etc. I can choose to display any of the readings on a graph (to check for trends), as a number, or on an analog dial gauge. I can also record a series of these datapoints to playback later or download to the computer.

Since I would expect if my aftermarket scan tool has these capabilities, the factory scan system would have at least this much capability as well, and that any of the technicians at the dealership are trained in using it. If they were to record the various readings after the car's sat in the lot overnight, then again when the car is malfunctioning, there's a good chance something may jump out at them as being an area for concern.

-Rod

[rhanson1]

Very interesting. I wasn't aware that a scan tool would yield that kind of detailed information. It makes no sense to be taking things apart and replacing components on a hunch when you can get that kind of definitive information. I checked out the OTC website and watched their demonstration video on the Genesis. Pretty impressive.

I agree that one would think that the dealer's diagnostic equipment would be at least as sophisticated as your aftermarket scan tool. I'm going back to the dealer and insist that they diagnose this problem properly. I am able to give them a lot better description of the problem than I could before, and the problem is easily demonstrated. I'll let you know how I make out.

[shorod]

Good luck!

While you're insisting they properly diagnose the issue, you may want to get an estimate from them for the diagnosis. If you leave it open ended and they for some reason spend a bunch of hours looking into the issue, it could get expensive. It wouldn't surprise me if they charge you nearly $100 just to connect the scan tool.

-Rod

[rhanson1]

Brief update. I sent a very polite and friendly email mesage to the service manager at the dealership requesting his assistance. I explained everything about what was happening and requested that he contact me via phone or email. It's been 28 hours since I sent the message, and so far no response. Not encouraging.

On a more encouraging note, I think I've further narrowed the source of the problem. I don't know why I didn't try this before, but I discovered today that if I manually turn off the AC with everything else is in automatic mode, the outlet vent temperature turns warm like it should be, and the system seems to operate and regulate normally. When I turn the AC back on, the air temperature coming from the vents starts to plunge again. This discovery is making me suspect that the problem may be what you suggested way back in one of your earlier posts: the evaporator discharge temperature sensor. And fortunately that's the easiest one to access. Since these sensors are relatively inexpensive, I think I may replace it to see what happens. I think it's probably a safe bet that my dealer doesn't have it in stock, so I might as well just order it online someplace. Let me know if you have any suggestions on where to order it from.

I originally thought that the only purpose of the evaporator discharge temperature sensor was to keep the evaporator coil from getting so cold that it freezes it. That assumption was based on how household AC systems work, but perhaps automotive AC systems are different. Certainly if the sensor is sending a false signal to the EATC module telling it that the evaporator discharge temperature is very warm when its not, that could explain why the AC is coming on to cool the air. It would also explain why both the drivers side and the passenger side vents behave the exact same way. What is doesn't explain is why it takes 15 minutes or so after a cold engine start for this problem to begin. Perhaps that's how long it takes for the underdash temperature to warm up from the engine heat, and maybe that warmth is throwing off the temperature sensor - I don't know.

[shorod]

I've been pleased with the service from this online store. You can look up by application or by part number if you have the old sensor out.

-Rod

[rhanson1]

After further investigation, I don't think there's anything wrong with my evaporator discharge temperature sensor. I removed the device from my center plenum and put an ohmmeter on it. It seems to behave normally. I get a reading of about 50 ohms at room temperature. As I move the sensor to cooler or warmer locations, the resistance goes up or down in a linear fashion accordingly. Also, with the evap sensor missing from my climate control system, it still behaves exactly the same way - everything is fine for about the first 15 minutes, then the air coming from the vents starts getting progressively cooler.

I'm at my wits end trying to figure out what the problem is. I don't believe that there's a problem with either of my heater core temperature sensors because the drivers and passengers side both behave identically. I don't believe that there's anything wrong with the cabin temperature sensor because the blower speed increases as the difference between the cabin temperature and the temperature setting increases, thus confirming that the cabin temperature sensor is sensing properly.

About the only thing left that I can think of to explain what my system is doing is a bad EATC module. That has to be an expensive item, but at least the removal and replacement is easy.

Still no response to my email message to the dealer. Perhaps I need to find a different dealer. Someone with proper diagnostic equipment must be able to find the problem here so that I don't have to shotgun replacement parts. I wish I could find some literature explaining exactly how this system operates so that I could diagnose it more accurately based simply on what it is and isn't doing.

[shorod]

Since you've removed the Evap sensor, what's the harm in swapping it with one of the others? You may have read my other post where I didn't see a huge difference in ohmmeter measurements between the suspect sensor and the passenger sensor, but I swapped them and the system seemed to function properly. It would take you probably less than 15 minutes and would answer a question or two.

-Rod