AC evaporator and (probe)

[Bobbycat]

CM,
Yeah, I was going to install the other sensor as a backup next to the original one, that way if there was a failure I would only need to gain access to the thermistor plug to use the backup. I wouldn't run them in parallel, a would think that would show the controller 1/2 of the resistance it should see at a given temp.
I'll check the controller when I check the wiring and report back.
Thank you,
BC

 

[Bobbycat]

I tested the harnesses and took the controller apart today. Mine is completely different than the pictures of the one Chris provided. All of the solder pins looked good, but the way it is built is totally different. The speed switch for the fan is actually in the back half of the case and extends through the front with a long knob spindle. Speaking of knobs, they need to be all the way to right to remove them.

 

[Christopher McKenna]

That's the older controller model. Can we get a part number / PN for this one please? That way, we'll have the PN on hand to which, can be accessed herein this thread and the database I've been compiling.

Thanks,
CM

 

[Bobbycat]

I tested the harnesses and took the controller apart today. Mine is completely different than the pictures of the one Chris provided. All of the solder pins looked good, but the way it is built is totally different. The speed switch for the fan is actually in the back half of the case and extends through the front with a long knob spindle. Speaking of knobs, they need to be all the way to right to remove them.
View attachment 129147View attachment 129148

Controller part number is 55056323AC

 

[Bobbycat]

Chris,
I'm thinking about installing the spare thermistor at the same distance from the top/bottom, but closer to the HP inlet pipe. I would think that the EVAP core would be coldest near the inlet? Any thoughts? Ideally, in hindsight, I would have drilled a small hole in the heater box and ran an inspection camera inside to watch were the ice starts, and put the sensor there (hopefully the TSB for relocating the sensor is in that spot).

 

[Christopher McKenna]

There we go. Now then, with this in mind, I'm curious as to what the thermistor assembly looks like that mates up to this controller.

I'm wondering about something seeing how this is a different configuration controller. Has the vehicle always iced up since you've had it?

Do you happen to know if the thermistor assy was ever changed out during having the HVAC serviced?

I have a hunch here on another possible root cause but, am going to wait until I see the two thermistors that were tested.

Thanks,

CM

 

[Bobbycat]

The top sensor in the middle picture is the '03 one. The other two pictures are of the '02 sensors tags.

 

[Christopher McKenna]

The ice-over condition at the EVAP CORE, on 2003 models, per engineering, was due to a misplaced thermistor probe. That was the root cause for freeze-ups. The engineering firm that caught the error in the wild through mechanics had notified dealerships all over the country about the error. However, there was, not to my knowledge anyway, ever a TSB published and recorded that updated it at the documentation level. The only people that knew about it were dealerships and, at that, it was sketchy due to some dealerships in the present, not having this information and, using the old-location called out in the service manuals which, are still in error as of today.

That was the No 1 Root Cause from the factory floor. It wasn't until 2005 that Mopar updated the rigs on the line where the thermistor probe location was updated.

Our other No 2 Root Cause was at the garage and dealerships over the course of servicing. What would occur is mix-n-match controller to incorrect thermistor.

Another catastrophe involving an even worse case scenario involving multiple part numbers were noted for pressure switches for the same make and model. That was what was a root cause that led to blown systems.

On my 2005 2500 Cummins, I've got two pressure switch PNs. Here's some info on how this occurred. The high-pressure rail side for my rig comes with a pressure switch installed. But, the build-book configuration lists another PN for that pressure switch that is supposed to be used in the rig. I have both configurations on hand hardware wise thus, I can assure others, it's not just a nomenclature issue with BOMs and parts houses. There's a lot of confusion in configuration changes over the years.

This is why some were blowing up post excessive pressure build-up. By design, the failsafe mechanism designed in was to release pressure via that pressure sensor mounted to the high-pressure rail but, often enough, the switch didn't do its job thus, the compressor relief valve would blow or worse, the catastrophic failure would occur thus, taking out the entire HVAC system. Huge costly bill incurred as a result.

I know that "somewhere" in the course of time, a change was made to update models to those pressure switches as standard failsafe mechanisms.

CM

 

[Christopher McKenna]

This is out of the service manual - thus, as shown, the thermistor probe location is in the upper right hand corner. This is where the root of all the ice-overs emanated in the beginning starting with design and whomever the tech writer was that worked on the HVAC section for the manual. This is the incorrect location for the thermistor probe. The service manuals resulted in the hardware shown in Fig 2. Thermistor Probe ASSY Incorrect Probe Location at the EVAP CORE. This was what occurred since, about 2002-2003 until year 2005 where OEM Mopar updated it on the factory floor. However, the service manuals still show the incorrect location. This still confuses the heck out of mechanics as, those manuals are still referenced.

 

[Bobbycat]

There we go. Now then, with this in mind, I'm curious as to what the thermistor assembly looks like that mates up to this controller.

I'm wondering about something seeing how this is a different configuration controller. Has the vehicle always iced up since you've had it?

Do you happen to know if the thermistor assy was ever changed out during having the HVAC serviced?

I have a hunch here on another possible root cause but, am going to wait until I see the two thermistors that were tested.

Thanks,

CM

I bought the truck from the original owner 5-6 years ago, and I asked him if there was anything wrong with the truck, he said that the AC would ice up sometimes. I don't think he ever had it looked at, and it didn't look like it had ever been apart (I'm really particular about fastener location).

 

[Christopher McKenna]

So what we've got here I'll bet is, the No 1 Root Cause for ice up that the original owner reported as occurring to him as well. This goes back to a design issue / error. Using logic here, I am willing to state that, I'll bet that once you relocate the OEM thermistor probe to the correct location, all your ice-over issues will be resolved.

I can tell you're detail oriented there and that's a good thing. The only sad aspect of these older models involves obsolescence of certain parts and components. I love these 3rd gen models - in particular, the 05s.
Keep the updates coming and we'll see how things turn out once things are put back together.

One question that I wanted to ask was, does your vehicle have a high-pressure switch located on the pass / right side of the vehicle near the wheel well by chance? Reason being, I'm trying to trace out when this was phased in. I'm seeing a recall alert in my memory about this and am trying to get the timeline put together as far as when that cut-in was made. I know the 2005 had it installed off the line but, there were a few years that didn't sport this design.

Thanks,
CM

 

[Bobbycat]

Yeah, if it still freezes up after all this, I'm going to loose my ****.
I like the DR body trucks also, but I feel the early ones like mine had some serious shortcomings. I have upgraded a ton of parts, 2009 steering box and linkages, free spin hub conversion, single piece aluminum rear driveshaft, etc. I've spent a bunch of money to upgrade parts that really should have already been on the truck.
I checked for the sensor you mentioned, and the only sensor I can see in the entire circuit is a two wire one near the compressor.

 

[Christopher McKenna]

I got mine second hand from a Mom & Pop flip-this-truck joint in TN and, drove it since 2011 till about oh, 2017 without maintaining it. Mostly cross country back and forth non-stop till deciding to change injectors after noting a rough running and slight smoking condition. Once I started down that path, I decided to gut the entire vehicle. Gone were the dreadfully uni-bearings at the front axle to the OEM fuel pump which was mounted in the tank to an up to date poppet valve aerospace pump sporting vortex air and contaminant filtration plus heat for winter in Montana and Wyoming climates. The list keeps going. Mine - only gave me grief with the uni-bearing on the right side and disposable steering. I gutted all the steering 100% and now, it's 100% user field replaceable on the fly provided one have spare heims on hand. Everything - from the fuel system to steering system has been updated to facilitate changes on the fly per diem. I live on the road for work so, I can't have down time while traveling. The transmission - that's the next overhaul item. I'm very fortunate not to have had transmission issues on both of my rigs. The 96 transmission is still rock solid and shifts smooth as silk despite 300,000 plus miles. The 05 model is the same but, I know the transmission overheats on mountain passes thus, I try to keep my foot light and give it a break to avoid burning the fluid by driving it hard which, it will no problem but, I've gotta update the cooling system for that to prevent thermal damage.

The transmission is the weak link so far. The engine - runs like a top with the new Dynamite Injection system on there. No issues there but, the intercooler to radiator and all silicone cooling lines were updated. The turbo is still rock solid without runout but is old so, that would also need to be updated. The wiring harnesses are atrocious and are an atrocity by design. I won't even go into that, as, that's not applicable here so, anyways, getting back to HVAC mode here, looks like your year did not include the high-side pressure switch.

See if there's a recall to update that high-side line to the latter model. I barely remember but, I seem to recall something about a recall and update to the later configuration that was retroactive that encompassed the older models.

Regards,
CM

 

[Bobbycat]

I got mine put all back together a couple of weeks ago; only ran around town locally a few times with it so too soon to tell, but has not froze up yet. For anyone who pulls their dash our to fix the freezing issues and also has the 500 piece Dodge OEM crappy dash, the replacement from LMC truck appears to be made with the original factory tooling (it's a lot cheaper than one from Mopar, but still pretty spendy). It fit perfectly, down to every last screw and clip, and comes with all of the correct anti-squeak pads installed in the correct locations.
The only fault that I can see in it is that the color is slightly lighter in color than the original dash, but this one is supposed to be made from a different material that won't crack. I replaced the dash in my 1996 for the same reason, and that one I replaced with the Mopar "update no crack dash" (because I still was getting employee pricing at the time), and it was also slightly lighter in color. So hopefully my crack dashes will finally have their lives cleaned up and straightened out for good.
I will report back after I run my truck in conditions that would normally freeze it up.
Chris, thank you for all the help.

 

[Bobbycat]

Once I started down that path, I dec won't even go into that, as, that's not applicable here so, anyways, getting back to HVAC mode here, looks like your year did not include the high-side pressure switch.

See if there's a recall to update that high-side line to the latter model. I barely remember but, I seem to recall something about a recall and update to the later configuration that was retroactive that encompassed the older models.

Regards,
CM

I'm not sure how it would/could be installed, as it would need wiring and probably a new controller to take the additional sensor input (unless it just tied in through the compressor clutch coil circuit?). I will check on it and see.
As far as I know, the only open recall on my truck is the airbag bracket, which I had all that out to replace the dash pad and it is fine.

 

[User113]

So, just to recap, pic is post #129 is incorrect; pic in post #37 is correct; but I can't mentally square the two, it seems that the probe wire is coming in from opposite sides. Is the evaporator in #37 upside down relative to the photo is #129? (I read post #33, but that didn't help, but I do not have my air handler unit open in front of me...)

 

[Christopher McKenna]

So, just to recap, pic is post #129 is incorrect; pic in post #37 is correct; but I can't mentally square the two, it seems that the probe wire is coming in from opposite sides. Is the evaporator in #37 upside down relative to the photo is #129? (I read post #33, but that didn't help, but I do not have my air handler unit open in front of me...)

The HAD / HAA in the photo is upside down thus, the placement of the probe shown in the incorrect position - also as seen / shown in the User Service Manuals till this day, show the bottom side of the EVAP CORE not the top side where the plumbing exits the HAA unit through the firewall interior cockpit to the engine bay side of the firewall.

The EVAP CORE showing the thermistor probe location involves the bottom side that sits in the foam drip tray. The thermistor location shown in both service manual and in the other image that represents the incorrect location under the service manual image - that is the bottom side of the EVAP CORE that resides in the drip tray.

As to why that was shown that way in the Service Manual - either the tech writer got his or her wires crossed or, engineering drove that off their CAD systems and someone either inverted the probe location and was in error or, engineering chose that location assuming it wasn't going to be an issue.

What I presume was occurring from an engineering stand point was, the water run-off was warmer than the upper limit threshold of the upper limit setpoint programmed into the controller thus, the probe never reached the max limit because it was stuffed inside the drip tray where warm water was accumulating thus, all the controller was measuring was the temperature of the water thus, keeping the compressor in-circuit non-stop. The controller had no idea there was an ice over going on above the warm zone thus, what was probably the root cause for years worth of ice-overs coming off the manufacturing floor since 2002-2003 era.

Regards,
CM

 

[Christopher McKenna]

I got mine put all back together a couple of weeks ago; only ran around town locally a few times with it so too soon to tell, but has not froze up yet. For anyone who pulls their dash our to fix the freezing issues and also has the 500 piece Dodge OEM crappy dash, the replacement from LMC truck appears to be made with the original factory tooling (it's a lot cheaper than one from Mopar, but still pretty spendy). It fit perfectly, down to every last screw and clip, and comes with all of the correct anti-squeak pads installed in the correct locations.
The only fault that I can see in it is that the color is slightly lighter in color than the original dash, but this one is supposed to be made from a different material that won't crack. I replaced the dash in my 1996 for the same reason, and that one I replaced with the Mopar "update no crack dash" (because I still was getting employee pricing at the time), and it was also slightly lighter in color. So hopefully my crack dashes will finally have their lives cleaned up and straightened out for good.
I will report back after I run my truck in conditions that would normally freeze it up.
Chris, thank you for all the help.

Just seeing this today - sorry for the delay here. You're welcome BC. Hope it works out and works reliably as well without faulting like it was prior.

Regards,
CM

 

[User113]

CM,

Well, some of my HVAC doors have finally failed and I am waiting for replacements from Blend Door USA. Please excuse the brief sidetrack here.

There is a lot of really good info here, so while I was going back to review what you had said about the evaporator temp sensor position I noticed that in post 38 of this discussion you had teased us with a comment regarding the original foam seals and replacing them with a better material (emphasis added):

Now, with these Dodge Ram HVAC HAA systems in general - they should be gutted and overhauled and improved beyond the OEM design. While the mechanical engineering was spot on with the mold of the HAA / HAD upper and lower half along with ingenious cooling for the blower motor, there were serious flaws at the materials engineering level. In particular, the doors and seals.

The door material was brittle and over time, it would stress under torque loading thus, fatigue failures are still common. All the doors should be gutted and replaced along with all the foam seals throughout the distribution center and dash duct level. Blend door dot com sells nice aluminum doors. However, the seal material will dry rot over time thus, if one is ambitious enough, the foam should be replaced with a more reliable and long-life material. If anyone is seeking information on how to overhaul and what materials to use, please feel free to inquire. One will want to use HD actuators rated for high current / high torque applications to ensure tight seals and long life.

Since overhauling my rig towards a global expedition vehicle, I gutted the dash down to the frame and am redoing the wiring as needed thus, it was easy to gut the entire HVAC system from engine bay to cockpit in a single go. I had the time to tear-down and source materials suited for the end-use environment and application that will outlast the OEM design.

I definitely need to replace the seals in my truck and I was about ready to go to Lowe's for some Frost King self-stick weather seal when I ran across the above invitation which made me question my decision. So I am officially inquiring as to what your research has uncovered in this regard. What can you tell us, please?