AC evaporator and (probe)

[Christopher McKenna]

Now we'll discuss those values that were posted above there.

OEM THERMISTOR VALUES:

1. R100 VALUE: 58 OHM @ 100C.
2. R25 VALUE: 5K OHM @ 25C. This is its prime parameter measured at 1-ATM @ AMB / 25C. This can be called T1.
3. R0 VALUE: *~16K OHM @ 0C. *NOTE: For sake of argument: ice water undisturbed, assumed temp at ~0C.
4. R-22 VALUE: 58K OHM @ -22C
   

After reviewing the data presented, I don't believe you have a faulting / faulty thermistor. Both the junkyard model and OEM model that you have appear to be fully functional and operating normal. If you saw dropouts during transitioning (ERR / OF) on your DMM, then you can retest to verify it's not an anomaly during test or, due to probe issues etc. But, if all were fine during both modes (Ramp Down and Ramp Up) - the sensor assy is functional.

What you may have is a problematic controller or fault - elsewhere in the HVAC control system. I recommend opening up the controller (I can provide pictures of the gross-workmanship / quality issues) and inspecting it along with the smaller wire harness feeding the controller and the harness at the HAA / HAD that ties into the Thermistor Harness ASSY.

I have all the harnesses out so, at any time you need to physically see how the interconnects mate up - I can help provide images and detailed call outs if needed. Although, it may take me a bit as, I'm running another project concurrent so, I may not be able to immediately generate the necessary documentation on the fly.

CM

 

[Lorenzo816]

I would definitely like to go further on this controller.
I am not hesitant to work on electrical components.
Where do we go from here on this?

 

[Christopher McKenna]

Over coffee, I am going backwards in this thread to review some comments and came across this one:

"Currently my thermistor is on the outside of the box because when its on the inside it is reading faulty causing the ac clutch to kick on/off every few seconds."

That there is something to investigate because, that's not normal. I need to go back and refresh myself with the particulars in this case to help you root this out - starting with year, make and model and to which type of HAA control system you've got, which controller you've got and which thermistor is employed. It's been a while so, apologies for having to re-review this case but, that's not normal at all.

If it is kicking it off immediately when run inside the HAA / HAD but not when run outside the box, that is telling us something.

Walking the path, that indicates that either the temperature of the EVAP core is already at or below the MIN setpoint value called out at the software level running on the controller OR:

The controller lost its calibration on its comparator circuit either a hardware fault or at the software level.

<IF> the sensor is functioning, there is a strong indication that the root problem exists at the EVAP level / zone inside the HAA or Controller itself.

If no other change was made such as, use of bypass harness, junction box, jumpers etc, and the HVAC works outside but, not inside the HAA / HAD, that's where the problem is rooted. I think we're dealing with a control system level anomaly.

 

[Christopher McKenna]

Lorenzo, I read in your signature that you've got a 2006 but, do you happen to have the thermistor that mounts inside the EVAP core or, the latter model sporting a plug-in thermistor assy.

I would like to ensure I know which system and thermistor is involved with your model just to refresh my own notes here this morning. I want to ensure I have the correct configuration on my end. This will help me to avoid rooting out issues for another system vs. your configuration.

Dodge introduced some changes to the thermistor type sometime in 2006. I have a mid 2005 model myself. I have the model that requires one to open the HAA Clam-shell molded case to access the thermistor harness assy. This carried over and into year 2006 if memory serves me correctly but, somewhere during the transition period, there was a design change which involved the thermistor itself and how it mounted / accessibility. This was when they introduced the HAA mounted thermistor assy which, I believe was an air-flow type vs. surface contact thermistor type as was employed from 2003 - 2006.5 (ish).

I will admit, there's some "gray" area on when that transition took place on me end. It's been a while thus, I may be in error on the timeline.

But, what type of thermistor mount style do you have employed on your rig?

Regards,
CM

 

[Lorenzo816]

I'm betting it was an internal on the evap unit because my housing was sliced open and then taped back with hvac foil tape. Would you like me to take a picture of the box assembly?

 

[Christopher McKenna]

Yes please.

I would also like to tell you I appreciate your patience with this thread etc. I'm going about it but, it takes time which, I know this is a pain because the vehicle or problem resolution is needed ASAP.

I will take all this information and add it to a working file that I maintain in my database that I've compiled, complete with PNs (BOM) for varying configurations.

Is it possible to remove the HVAC controller and snap a picture of its PN? I need that info as well.

I have a growing suspicion of a possible root cause here. I will wait until I have more information on hand before jumping to conclusions.

Regards,
CM

 

[Lorenzo816]

I'm actually not sweating like i was weeks ago.(literally its cooled off from 90+ degrees thank God)
We also found a bcode or ucode I don't remember which that pointed us in the direction of the evap temp sensor lost communication or short.
I noticed when I got into the glovebox that the wires were poorly tied together.
So I used connectors and heat shrink to redo the mess. I noticed that when I put the temp sensor inside the unit that the clutch would cycle every five -10 seconds.
Our pressures on high and low looked good when it was running and the transducer was good too.

Here are some pics from the truck and a snapshot of the page from the dodge manual.
Says that the temp sensor resistance should decrease as temperatures decrease.

Shouldn't my resistance in ohms when I did my test have shown lower numbers thus increasing the current? (slightly confused here.)

The alpha numberic on the bar code is this:

58024B Rev-A P55056756AB 5/9/06 12:41

 

[Christopher McKenna]

Hello again. I will be reviewing this shortly.

Here's a huge breadcrumb herein the following statement:

1. Manual says Ohms / Sensor Resistance (R-Values) should decrease as temperature decreases. This is a clear indication of a mismatched system to sensor. Another possibility is incorrect manual for given year, make and model / configuration.
   
   For the sake of argument, let's just assume the manual you have is correct and that the information regarding sensor function is also correct. That would indicate that the sensor installed in the HAA is incorrect.
   
   TECH INFO 101. THERMISTOR TYPE
   
   TYPE 1: NTC (Negative Temperature Coefficient) RESISTANCE DECREASES AS TEMPERATURE INCREASES.
   TYPE 2: PTC (Positive Temperature Coefficient) RESISTANCE INCREASES AS TEMPERATURE INCREASES

Since the thermistor you measured, shows a decrease in resistance at a hotter temp (AMB vs. COLD), (~5K @ AMB VS. 16K COLD) - that means, the thermistor installed, in your rig, is of an NTC type. Problem is, a mis-match, per manual, was just uncovered and brought to life.

Per manual, manual says it is supposed to be a PTC thermistor. This would explain why running the sensor outside the HAA worked at AMB but failed to run when installed in cold air-stream in EVAP Zone in HAA.

The controller is expecting a decrease in R-Value (OHM) as temperature drops at the EVAP Core but, it is seeing an increase off the NTC Thermistor thus, triggering shut-off command to PWR RELAY which, in turn, cuts GND to compressor motor A/C Clutch via wire harness.

Again, that is based off that manual that you've got there on hand. If that manual is incorrect, disregard the above. But, if the manual is correct for your configuration, you're going to be seeking a PTC thermistor assy. This is odd, as, they typically do not employ PTC types for HVAC but, I've seen it myself so, I'm not going to exclude or disbelieve anything at this point.

This is where I believe the root cause to lie and, to what I had suspected. You've got a NTC Thermistor ASSY mated up to a controller that is designed for a PTC. That said, that's according to the manual. Also - as a side note, avoid jumpers, lengthening harnesses (impedance & capacitance changes) or adding additional connectors, splices, wire-nuts and so forth. The circuit (comparator) is calibrated for a given configuration. With these HVAC sensors, it can throw the entire circuit way out of whack.

This is why we needed to see the actual controller PN that's installed because, I've dealt with folks flipping Ram trucks and seen 1st hand this sort of thing occur down to using electronics from another controller stuffed inside the housing marked for another controller thus, making it difficult to troubleshoot via PN. I had to physically start opening modules and tearing out all the wire harnesses.

I've had to email Mopar a number of times over the years asking for build-out sheets per VIN code involving flipped rigs. I found entire bodies to chassis swaps and a myriad of electronic configuration swaps to *******ized harness work all the way to interior swaps. It isn't uncommon to see this occur actually.

This is why I wanted to back it way up and find out what configuration is physically in your rig.

CM

 

[Lorenzo816]

Totally understand and I'm betting the manual had a misprint. The VIN for my truck produce the NLA part number, which evidently brought me to TDR and to your thread.
If anyone else has an '06 and would like to pull their evap temp sensor out to compare, this oughta be fun.
We could also buy a resistor with a lower than 5k ohm value and see if what happens.

 

[Christopher McKenna]

After pulling up my service manuals for a 2005 year, SEC 24-231 also lists the same typo. I think I know what they did - disregard the manual - typo for now. Either we have a case of using outdated info that wasn't caught from a previous design carried over or, they meant voltage drop - typically voltage drop on the other side of a fixed R-VALUE at the controller.

This is why we employ tech writers who understand the technology. In the 2005 manual that I've got, I've encountered a plethora of gross errors in the torque tables alone. I've caught quite a few conflicts in the manual sections with regards to torque across the systems.

This comes as no surprise here either.

CM

 

[Christopher McKenna]

So, assuming that we've got the correct PTC thermistor installed, the next step should be to determine what we're dealing with and what we're supposed to be dealing IAW OEM build sheet.

Ground zero is the OEM build sheet. Then we compare to see what we are we working with.

Then we can proceed to the next step of figuring out WHY something isn't working.

 

[Christopher McKenna]

So far, PN for your controller appears to be the correct PN for a 2006.

There appears to be an issue with the thermistor for some 2006 models.

This is because there were TWO different thermistors used in 2006.

This can get confusing. We can ask why is the compressor short-cycling. But, if it was short-cycling, the pressure would be off on the lo side and hi side lines. Compressor kicks on, draws, pulls lo-side line down thus starving compressor input thus, power is cut, compressor is <OFF>. Pressure builds back in lo-side and then compressor is <ON> and the short-cycle condition repeats.

Problem is when rooting it out, that mechanical problem (which that is) doesn't occur in your case when thermistor is run outside the HAA ASSY. I will bet the HVAC system will run anywhere above freezing or, within 5 to 10 degrees above freezing.

And you can test for that since your thermistor assembly is outside the HAA ASSY.

I would also like to probe the harness extension with those crimps and check for high-resistance in that extension.

TEST SECTION:
Test HVAC system for short-cycle condition by subjecting thermistor to various temperatures outside the HAA ASSY. Starting at AMB (No need to test hotter than ambient for obvious reasons). I want to start with warm water and drop temperature slowly while monitoring temperature and resistance that triggers short-cycle condition.

I also want to verify that there's no excessive resistance in the wire harness assembly between thermistor and controller input. If harness assembly is adding resistance, compressor will shut off before OEM setpoint. We want to know whether or not the harnesses are introducing a high-resistance condition or not.

All should measure ~ 0 (ZERO) OHM over length of HAA harness (PIN TO PIN) AND dashboard to controller harness.

HARNESS TEST PROCEDURE

1. BREAKOUT DASHBOARD HARNESS TO HAA HARNESS CONNECTOR JUNCTION.
2. DISCONNECT HAA CONNECTOR TO DASH CONNECTOR
3. VERIFY RESISTANCE FROM HAA LARGE MAIN CONNECTOR, THERMISTOR PIN 1, TO THERMISTOR BREAKOUT CONNECTOR, PIN 1. NOTE: SHOULD MEASURE 0.3 OHMS
4. VERIFY RESISTANCE FROM HAA LARGE MAIN CONNECTOR, THERMISTOR PIN 2, TO THERMISTOR BREAKOUT CONNECTOR, PIN 2. NOTE: SHOULD MEASURE 0.3 OHMS
   
5. VERIFY RESISTANCE FROM LARGE DASH CONNECTOR, THERMISTOR PIN 1, TO THERMISTOR PIN 1 AT SMALLER CONNECTOR (P1) AT CONTROLLER.
6. VERIFY RESISTANCE FROM LARGE DASH CONNECTOR, THERMISTOR PIN 2, TO THERMISTOR PIN 2 AT SMALLER CONNECTOR (P1) AT CONTROLLER.

THERMISTOR TEST PROCEDURE

1. WRAP THERMISTOR IN SARAN WRAP OR EQUIVALENT
2. START WITH COLD TAP WATER
3. INSERT PROBE IN WATER. SOAK TIME = 5M (MINUTES) (record temp vs. OHM reading)
4. ADD FRAGMENTS OF ICE (record temp) SOAK TIME = 5M (record temp vs. OHM reading)
5. CONTINUE ADDING FRAGMENTS OF ICE UNTIL SHORT-CYCLE CONDITION OCCURS.
6. NOTE: COMPRESSOR CUT OUT OCCURS BEFORE 0-DEGREES C. Typically by design, controller software setpoint is 5~10-degrees above freezing to prevent ice crystals from forming on EVAP Core.
   
   
7. SLOWLY INTRODUCE HOT WATER.
   NOTE: when short-cycling condition goes away, you will know what's happening and at what temperature and at what resistance compressor is kicking on and off.

Despite that being a quick & dirty test, it will tell us what we need to know. We want to know at what temperature the compressor is cutting in and out.

Either we've got high-resistance in the crimp-splice junction, high resistance in wire harnesses, the wrong thermistor installed, to lastly, we have a controller issue. The controller runs that entire system so, if the HVAC system works / runs fine - non-stop when the thermistor assy is pulled out of the HAA ASSY, that pretty much isolates it down to the control system and its interconnects.

If it were another type of problem rooted say, in low refrigerant - there's another failsafe mechanism that addresses that issue and, it would occur any time the HVAC system compressor was engaged. The Safety switch would cut that out of circuit regardless of where the thermistor was running or, if one jumped in a fixed value resistor.

Regards,
CM

 

[Christopher McKenna]

In my reading, not only were there two different thermistor assemblies employed, there were also two evaporators as well with the latter model (PN 68004242AA) to be used with the latter style air-flow sensor that stemmed out of a succession of part numbers that came in succession post OEM PN 5140727AA. To add confusion, some vendors still show listings of the old OEM probe design that the 2003-2005.5 and early to mid 2006 models had installed for the new style, air-flow sensor PN which really makes it confusing for those who don't know the history.

On dealership lots new and in the dealership repair centers - the use of two different thermistor sensor designs was confirmed for same year, make and models - in particular however, The 2006 Dodge Ram Mega Cab models seemed to suffer more so, both gas and diesel models were affected. Somewhere along the line a transition took place then, supercedeing PNs for both EVAP thermistor sensor assembly and EVAP Core.

That brings one more question into engineering and that is, does the new air-flow sensor and new EVAP Core require an updated controller revision in order to function properly or can users plug & play with existing controllers?

https://www.moparpartsoverstock.com...-Evaporator-Fin-Probe/6909943/05140727AA.html

NOTES: The 2006 EVAP Core is reportedly, ~4.000-in depth coming in at 3.700-in thick. That's almost 1.00-in thicker than the predecessor core that was 2.75-in deep on the mid 2005 models. That begs the question, if the core depth increased on 2006 models, the sensor length should have also been updated and assigned a new PN on the BOM vs. rolling over a 2003-2006 Thermistor Assy that was designed around a 2.75-in core. There's a design flaw there and to why I'll bet they finally upgraded that year - mid production, Ad Hoc with an air-flow sensor that plugs into the box, sports a bend aimed at the EVAP Core.

This particular year (2006) is associated with a common complaint and that is freeze-up after 30-minutes or so. This is looking more and more like a design issue from Mopar rooting in a configuration problem that stemmed out of an Engineering Change Order (ECO) that took place sometime in 2006. I'll be seeking out a TSB for that. This occurred on 2005 models during the transition period out of 2004.5 models as well - same type of crap was done back then but, not by Dodge but by STAR Engineering Group. They were the ones who published the TBS and notified dealerships about the mishap involving misplaced sensor location on the EVAP Core. To date, the manual is still incorrect and was never updated to my knowledge. The only place that change existed was on STAR's documentation and via emails to dealerships. That's as far as it went. Only mechanics in the know who remember that published the information to others about the change.

With the 2006 Models the common trend associated with freeze-up involved cutting the HAA / HAD on 2006 models. I keep seeing more 2006s all with the same modification and sensor replacements all with the same problem - Freeze-Ups - no air flow out of the vent because the EVAP Core is iced up and blocking the air flow. The bigger picture is starting to appear as I read more on the 2006 model and user complaints. This is and has been - a design issue that was Patch Adams - probably again, on a TSB.

I'll bet a Technical Bulletin (TSB) from Mopar Dodge or STAR is out for 2006 models for, this was, and still is, a problem just like it was going from 2004.5-2005 early DOM models. I'll bet the root cause is simply a configuration problem that mechanics to parts-houses, to private mechanics all the way up to dealerships themselves, may not even be aware of.

2005 MODEL NOTES: I know that the EVAP Core changed PNs applicable to mid 2005 Models as well. I have two EVAP Cores here that are very different in terms of density. The envelope is the same obviously due to constrained by the HAA Injection Molded Clamshell but, the layout and density and weight is different.

This is how this actually started and how the entire path went into making my own thermistor harness. I knew there was an issue involving obsolescence and, I had seen others trying to use the 2006 air-probe. Now I know why they were doing that.

 

[Christopher McKenna]

Quick Update on this. Been away on another hot project thus why this one fell through the cracks. I'll follow-up on this and wrap this up once I've completed the other project. I didn't forget - just been busy.

Sorry for the delays.
CM

 

[Christopher McKenna]

I'll be picking this back up this month and we'll wrap this project up.

Regards,
CM

 

[Bobbycat]

So I have been dealing with the freezing EVAP core problem since I bought my truck (used about 5 years ago), 2003 3500 with dual zone temp. I have to replace the 500 piece dash and planned on dealing with the block of ice for an evap core at the same time. Not wild about using a junk yard part (thanks for the help STAR), and found this on eBay:
https://www.ebay.com/itm/264943719843?hash=item3dafe055a3:g:z8QAAOSw3Vpftpja
Someone figured out a sensor that has the same values but different plug, and figured they would get paid for the effort to the tune of $200 per sensor. Anyone have any idea what this sensor is out of? The part numbers provided in the listing seem to be a dead end (or made up more likely).

 

[Christopher McKenna]

That sensor, by appearance only, is identical in looks as the model that was used in the 3rd Gen, 2005 Model Cummins 2500 sporting a single zone HAA setup. The connector is identical as well.

I have to pick this back up anyways and finish it (been busy) so, I wouldn't spend 200.00 on that - not knowing if your assembly is working or not. Typically, the thermistors were placed 180-degree out of proper location. This was due to a misprint / error in the service manuals. They were rolling off the assy lines with incorrect orientation due to a technical writer's or, an engineering error.

Somewhere on this site, I "think" I've listed out instructions on how to test the assembly and also, the proper orientation at the EVAP CORE level. I believe I placed dimensions on a photo.

I would start by testing your thermistor assy first - before buying anything as, it's the eyes and ears of the operation in terms of engineering function.

Currently, I do have a stack of alternate thermistors that I've got selected right here in front of me on the desk but, there's still testing required.

 

[Bobbycat]

Christopher,
Glad to see you are still active on here. I will try testing the sensor when I have the dash out to replace it. My original logic was to just replace the sensor (and put it in the correct location) when I had it apart, as a redundant (and hopefully correct) repair. I don't have any experience with any other trucks that have this problem, so I don't know if mine is typical of the wrong placement of the sensor or not; but mine will freeze and block airflow off completely if you let it run on its own. I assumed it would only partially block airflow if the sensor was working but in the wrong location? I just don't want to have to pull the heater box more than once.
Thanks,
Robby

 

[Christopher McKenna]

I understand what you said there regarding not wanting to have to remove the HAD ASSY more than once. Opening the lines once alone, requires replacement of the open lines as a rule of thumb so, it can get costly. While some do reuse the lines and driers, it's adding risk into the system. Especially, if the lines are left open for a period of time to atmosphere. It eventually winds up ultimately killing the HVAC pump in the end prematurely.

There was a problematic model and, I believe it was the 3500 if memory serves me correct. Those sporting dual zone systems (HAD) were more problematic than the single-zone (HAA) systems. We'll walk the path and help you out. Reliability of these components is typically long-life thus, it's not feared to use the OEM component that was originally manufactured by Bosch Germany if memory serves me correct again. I think most of this information may already be listed on this thread on who the OEM was and the history of it being cancelled with Bosch without an ALT PN from Dodge for a replacement vendor PN for aftermarket manufacturers. When I contacted them directly via email, they stated in writing, there wasn't any demand and, since this particular assembly wasn't a long-run model (Indicating: phasing in changes Ad-Hoc with constant Rev updates every six months) - they had no intention of supporting anything beyond what they deemed EOL. (End of Life).

 

[Christopher McKenna]

How the system controller functions by design intent is, the controller is looking for a temperature value in the form of voltage at one of its many inputs. When the voltage reaches a certain level, the controller is programmed to CUT the HVAC PUMP out of circuit to prevent ice-over of the EVAP CORE. This is cycling ON/OFF of the pump. There's a number of fishbones in the diagram when mapping out possible root causes for failure in these systems. Typically, if a component is not working, there's failsafe mechanisms that have been designed in to prevent run-away ice-over conditions from occurring. This is the worst-case scenario that usually ends up failing catastrophically. The EVAP CORE will then develop a leak or worse, blow, thus allowing contaminants (FOD) to enter the lines thus, blowing the compressor.

If the thermistor assy <INPUT>, isn't working, the system engineer typically programs a default, cut-power command to prevent the compressor from engaging. This is on open circuit condition. The list of shoots on this, can get involved. More on that later.

CM