intermittent ac compressor clutch

[FabricGATOR]

It is hot in there, most of the time, ...

Hey guys, I am new RAM 3rd gen but Mopar for years. I even rebuilt my own 41TE/A604 transmission. I am am also an hvac 609 tech.

So my brother gave me his 2004 1500 SLT that he bought new at the dealer, gave it to me just last Wednesday while I was visiting. He said it was hot in there and he just wants a new Toyota or something with a backup camera and sensors... I think he is crazy, new cars suck!

I rented a uHaul trailer and towed my car home in Florida with the truck (in late June 2023, for timestamp reference). I love my brother and I love this truck BUT the a/c would only work about 38% of the time and it almost seemed like it is tied to the window switch as when it starts to blow cool and I put up the windows, that is when it quits again...

It is certainly an electronic / electrical gremlin as IF/WHEN the compressor engages, it is almost too cool.

BTW, the windshield wipers are also inop. It had a CEL that was [power steering switch] and [PS pressure parameters], I put fluid in and it went away.

Oh yeah, I checked the fuses and played musical relays with AC related circuits. The first time I did it with the A/C clutch, I thought '' well, that was easy'' NOT!

I am a troubleshooter not a parts changer and I HATE the parts canon approach. Doing that can get real expensive real fast.



I evacuated and recovered and then put in the measured charge (well, I tried) as when it came time to start the engine to suck up the remaining charge from the machine, the darn clutch wouldn't engage. I thought for sure that I really broke it now BUT the next day when I returned to try and figure this out, low and behold, the clutch was engaged and the vents were blowing cool... of course the machine with the remaining r-134a was five miles away... When I get it all working as it should I will go and pull another vacuum and charge. A long, deep vacuum...



My initial thoughts were that someone had been messing with a Walmart 134 charge hose kit and likely put a slug of air into the system. Step one, put a known measured charge into the closed system.

My friend has a auto repair shop and all the good tools including Snapon and Autel scanners. The Autel I had didn't give me the ability to manually engage the clutch so I didn't finish the charge but I did change the receiver drier and both Schrader type service valves while I had the system empty.

This thing is killing me, there aint' nothing that is free AND easy.


These scanner shots are from the HVAC sections. I would read them, take a picture, then clear them and see what came back as a hard code.


I found this forum while searching for FSM and IPC and I studied it all day.

What I need is the Dodge/Mopar/RAM Body Diagnostic Procedures manual so I can get the values and procedure to check the refrigerant pressure switch and the evaporator temperature sensor.

My bet (my hope) is that it is one of those. And while the pressure sensor can (should) be able to be changes without evac the system, the evap temp sensor may need me to remove the airbox behind the dash, if not the sensors, then the PCM or the climate control head... I gotta be sure before I spend that kind of money.

IS ANYBODY able to offer insight, experience, or solution?
I am old school and when it comes to electronic controls, that is where my skillset runs a bit thin...

Cheers

BTW, I worked at this shop in the past and they would start throwing parts at it to see what fixes it. not cool.

 

[FabricGATOR]

additionally, Autel is connected and up to date via WiFi.. I found a HVAC update and I installed it too, that is when I really broke the poor truck because I couldn't coax the compressor clutch to engage.

Like I said above, it engaged the next morning and again this morning. but only for a short while... Its gotta be a sensor or a loose wire.

Maybe the IPC?

 

[FabricGATOR]

So today I got into it a bit more. It was hot today and my friends AC Shop was booming busy.
Three mechanics each had their own evaporator replacement.

I got out in the parking lot, in the overcast heat, and continued to run the scanner. Today the Autel was being used somewhere so I had to use the SnapOn Versus Edge.

I still didn't have the compressor engaging but I did find both the pressure sensor voltage and pressure indicated data AND the ETS (evaporator Temperature Sensor) voltage and temperature indicated data.

I saw that the ETS volatge was low AND that it was saying that the evaporator temperature was like 57º F.... there ain't no way, It should be reading more like 105ºF in there without the system running.

Luckily, one of the new evaporator jobs was a 2014 RAM2500. In the picture you can see what it takes to get at that air box to repair blend doors or change the heater core or evaporator.
Step one, evacuate and recover the refrigerant. TWO remove the steering column... Three, loosen the dashboard fasteners and put the dash in the front seats... After those three steps, it is all a piece of cake (this is not my truck shown)

IF you ever do this, you will want to use a very high quality part (They only use factory Mopar evaporator and heater cores for Mopar vehicles)

Above the white label, You can see the OLD ETS laying atop the airbox and behind it is where the new one is inserted. This newer vehicle makes changing the ETS easy compared to my 2004.

I took the discarded ETS from this vehicle to see if I could use it to identify my suspected electrical fault.

I removed my glovebox and reached up around to try to ***** identify the ETS connector. While moving wires and suddenly my compressor engaged. AhHa

Well that lasted all of about six minutes but I did see the Pressure sensor data and the ETS data (temperature and voltage) it still was oddly suspicious. at one point I read a voltage of 0.02 v and a temperature of 47.6ºF but the air coming out of the center vents was only 56º... bad juju!

Like i mentioned, it didn't last for very long before it was back to warm and humid.


I massaged the wiring again and now it has lasted and continued to last for ten on/off cycles.
SO, I am onto something... now, if only I had a wiring diagram so I could ohm out the wiring.

 

[FabricGATOR]

Puritan group we are, I see, I agree, but kinda goofy

 

[FabricGATOR]

SO this morning (late morning, just before noon) 90º outside with humidity (feels like) = 99º and my AC, sprung to life upon command.

Do I continue to mess with it or do I just accept that wiggle the wires and now it works?
More than likely a bump or giggle is probably going to make it fail again....

 

[MAC830203]

A lot of pinched wires will break on an old wire harness but give enough reading to show 12v. Cut’em, patch in new, solder and shrink with marine glue lined heat shrink.

 

[Sherman Bird]

It is hot in there, most of the time, ...

Hey guys, I am new RAM 3rd gen but Mopar for years. I even rebuilt my own 41TE/A604 transmission. I am am also an hvac 609 tech.

So my brother gave me his 2004 1500 SLT that he bought new at the dealer, gave it to me just last Wednesday while I was visiting. He said it was hot in there and he just wants a new Toyota or something with a backup camera and sensors... I think he is crazy, new cars suck!

I rented a uHaul trailer and towed my car home in Florida with the truck (in late June 2023, for timestamp reference). I love my brother and I love this truck BUT the a/c would only work about 38% of the time and it almost seemed like it is tied to the window switch as when it starts to blow cool and I put up the windows, that is when it quits again...

It is certainly an electronic / electrical gremlin as IF/WHEN the compressor engages, it is almost too cool.

BTW, the windshield wipers are also inop. It had a CEL that was [power steering switch] and [PS pressure parameters], I put fluid in and it went away.

Oh yeah, I checked the fuses and played musical relays with AC related circuits. The first time I did it with the A/C clutch, I thought '' well, that was easy'' NOT!

I am a troubleshooter not a parts changer and I HATE the parts canon approach. Doing that can get real expensive real fast.

View attachment 523844

I evacuated and recovered and then put in the measured charge (well, I tried) as when it came time to start the engine to suck up the remaining charge from the machine, the darn clutch wouldn't engage. I thought for sure that I really broke it now BUT the next day when I returned to try and figure this out, low and behold, the clutch was engaged and the vents were blowing cool... of course the machine with the remaining r-134a was five miles away... When I get it all working as it should I will go and pull another vacuum and charge. A long, deep vacuum...

View attachment 523845

My initial thoughts were that someone had been messing with a Walmart 134 charge hose kit and likely put a slug of air into the system. Step one, put a known measured charge into the closed system.

My friend has a auto repair shop and all the good tools including Snapon and Autel scanners. The Autel I had didn't give me the ability to manually engage the clutch so I didn't finish the charge but I did change the receiver drier and both Schrader type service valves while I had the system empty.

This thing is killing me, there aint' nothing that is free AND easy.

View attachment 523847View attachment 523848
These scanner shots are from the HVAC sections. I would read them, take a picture, then clear them and see what came back as a hard code.


I found this forum while searching for FSM and IPC and I studied it all day.

What I need is the Dodge/Mopar/RAM Body Diagnostic Procedures manual so I can get the values and procedure to check the refrigerant pressure switch and the evaporator temperature sensor.

My bet (my hope) is that it is one of those. And while the pressure sensor can (should) be able to be changes without evac the system, the evap temp sensor may need me to remove the airbox behind the dash, if not the sensors, then the PCM or the climate control head... I gotta be sure before I spend that kind of money.

IS ANYBODY able to offer insight, experience, or solution?
I am old school and when it comes to electronic controls, that is where my skillset runs a bit thin...

Cheers

BTW, I worked at this shop in the past and they would start throwing parts at it to see what fixes it. not cool.

I've been a professional auto technician since the first year that Catalytic converters were required.... 48 years. As time marched by and I worked in GM dealership, I was sent to school for the first generation of EEC systems and then OBD2 in 1996, and later on, LIN BUS/ CAN BUS diags.
The one thing they hammered into us was that, when you have multiple DTC's you must cure the one which denoted lack of communication FIRST, regardless of which module flags it. This has proven out for me many many times. I'm thinking the "checksum fault" is where the problem lies! Eliminate that one first.

 

[FabricGATOR]

The one thing they hammered into us was that, when you have multiple DTC's you must cure the one which denoted lack of communication FIRST, regardless of which module flags it. This has proven out for me many many times. I'm thinking the "checksum fault" is where the problem lies! Eliminate that one first.

Thank you Sherman for sharing your wealth of information and training with me.

Can you explain what the check sum fault is and how it would be cleared? Isn't it a handshake of sorts between all the modules and somehow this HVAC checksum ( some module or modules ) isn't to be trusted because it is not recognized as a member of the collective network?
I don't know, I am guessing...

Now, in my limited abilities, I wanted to test the evaporator temperature sensor as it was showing on both the autel i608 and SnapOn Versus EDGE scanner as being cold when the vehicle was actually hot.
So not really knowing what or where, I tried reaching my hand up around, gently molesting the wire harness behind the glovebox trying to feel what could be the ETS (evaporator temp sensor) connector and at some point is just started working. Then it remained intermittent so I tried more harness manipulation in that area and now the air conditioner has been working reliably for almost a month. BUT, the ETS (sensor) may still be showing low voltage, but it is working... and I didn't positively identify the sensor connector.

Back to the CheckSum Error on the HVAC page of the scanner... Is this something that the dealership can do without replacing a lot of expensive parts (the PCM)?
Is it just an polite introduction at a party?
A few swipes with a propriety DRBIII tool??
I am scheduled in a few weeks for another passenger airbag recall (third time is a charm)
It would be great if they would just recode everything for free.

My suspicion is that when some ham ****** dealership mechanic was in the dashboard trying the second or third time to replace the TATATKA passenger killer and maybe they had to get in around the hvac wiring??? And perhaps didn't properly make up the ETS connector? ...and now I stumbled upon it and although it may appear to be working for the interim, that I am still not sure the connector is made up, *[click N little red slide locked]


****** this is is stupid that my term ham fist ed (turn you hand into a little ball by wrapping your fingers tight) mechanic should be censored

 

[Sherman Bird]

Scanners lie to you. Some just flat out fail to display the data parameter you need/want/wish was there. I own multiple scopes and scanners to cover my backside. A checksum error code IS a communications drop out, whether for a split second, momentary, reactive to some other module knocking another one off line.

The fact that you can wiggle the harness and effect change of function says volumes about both your symptom and DTCs. You are on the correct track.

You have completed your first step of diagnosis by narrowing down WHERE a problem lies.
NOW, comes the difficulty of pin point testing in order to find the exact culprit.

My late Father was a systems engineer for IBM. He frequently said that in times of intermittent problems, it's better to get lucky than be good at it.

 

[FabricGATOR]

Thank you once again Sherman.

Better lucky than good... absolutely. Especially with all this heat, not having A/C in this new to me truck, it was not fun.

I also have a mode select function (defrost, vent, heat) malfunction so I chose to defer further investigation until the heat wave breaks. I will recover, and remove dashboard and the airbox and at that point I will be able to inspect and repair much better.

NOW, if say I am now making connection (*jinx) by happy accident, and that was a reason for 'checksum', is there any possibility that give a number of cycles, could it possibly clear itself? (I've tried to clear it and it is a hard set code [in the past])

I ask as another esteemed member on dodgeforum is fairly ascertive that I need a new PCM, and eventually the apocalypse will come (...not what I signed up for) ... and I am trying to wrap my head around how it runs so well and then it is going to have a network crash. Ugh

Wilbur Volker (1929-2008) would often say:
"Nothing is impossible for the man that doesn't have to do it..."

 

[Sherman Bird]

Thank you once again Sherman.

Better lucky than good... absolutely. Especially with all this heat, not having A/C in this new to me truck, it was not fun.

I also have a mode select function (defrost, vent, heat) malfunction so I chose to defer further investigation until the heat wave breaks. I will recover, and remove dashboard and the airbox and at that point I will be able to inspect and repair much better.

NOW, if say I am now making connection (*jinx) by happy accident, and that was a reason for 'checksum', is there any possibility that give a number of cycles, could it possibly clear itself? (I've tried to clear it and it is a hard set code [in the past])

I ask as another esteemed member on dodgeforum is fairly ascertive that I need a new PCM, and eventually the apocalypse will come (...not what I signed up for) ... and I am trying to wrap my head around how it runs so well and then it is going to have a network crash. Ugh

Wilbur Volker (1929-2008) would often say:
"Nothing is impossible for the man that doesn't have to do it..."

PCM/ECM.... these rarely fail. They do... but not very often. GM's assertion was that 96% of the computers returned as defective/cores were found in testing to have nothing wrong.
I had a lack of communication to the IPC (Instrument Control Panel/ Hybrid Electronic Cluster) on a 2002 Explorer back in 2002 when I was with Ford. This was a new car under warranty with under 4000 miles on it. It was tendered for warranty repair for an intermittent A/C compressor clutch failure to engage. (Customer's complaint was sometimes the A/C quit cooling sporadically. (Otherspeak for "intermittent")

The Ford Factory flow diagnostic chart and circuit tests showed to replace the PCM. Before it came to me, 3 had been installed by a combination of the A/C specialist and a drivability specialist.

Keep in mind, there were NO codes anywhere except in the instrument cluster for "Loss of communication" with the CAN network. In those days, it was called "SCP" Standard Corporate Protocol".

Having been trained by GM, and given that the month was August with 102 degree days, the customer contacted through an attorney, the head cheese at Dearborn, Michigan, screaming "Buy back"!

This prompted one of the field engineers to darken our doors at this mega sized dealership. NO Auto manufacturer wants to have to buy back a vehicle.

This engineer got it into his head that there MUST be a wiring problem and instructed the drivability and A/C techs to remove all the black plastic sheathing and commenced to isolate every underhood wire.

I was passively involved in that I'd checked the car out; I determined that the cluster should be replaced; a VERY expensive and committed move. The cluster cost the dealer 600 dollars, had to have the vehicle's VIN number and mileage burned into the prom chip.... a one time only and permanent commitment to THAT part. It could NOT be returned once the prom chip had been burned in.

Eventually, the engineer did put the cluster in it and 3 other Explorers in Houston dealers... and that procedure fixed them all. No PCM was ever needed.

 

[FabricGATOR]

Nice Win!
My friend with the AC shop had a sweet Honda Civic 38k bought at the auction. BUT no air conditioning... We changed everything, BCM, ECM, control head... and of course the compressor, etc.. We could manually cycle the clutch by forcing it through the scanner but normal operation was not happening (this car bought from a kia dealership auction trade in)

It took two and a half years of pinning out (as workflow permitted) and three unsuccessful trips to Honda dealership before someone suggested the instrument cluster... sure enough that did it.
Now how come the Honda dealership didn't think of that?

 

[Dodge 1500 4X4]

Read most of the post, next time when you're evacuating the system, disconnect the plug to the compressor, and make a jumper with a +- and feed it 12volts so you can complete the evacuation.

 

[Sherman Bird]

Nice Win!
My friend with the AC shop had a sweet Honda Civic 38k bought at the auction. BUT no air conditioning... We changed everything, BCM, ECM, control head... and of course the compressor, etc.. We could manually cycle the clutch by forcing it through the scanner but normal operation was not happening (this car bought from a kia dealership auction trade in)

It took two and a half years of pinning out (as workflow permitted) and three unsuccessful trips to Honda dealership before someone suggested the instrument cluster... sure enough that did it.
Now how come the Honda dealership didn't think of that?

B

 

[FabricGATOR]

Read most of the post, next time when you're evacuating the system, disconnect the plug to the compressor, and make a jumper with a +- and feed it 12volts so you can complete the evacuation.

It is not a switch like that, it is a pressure transducer that feeds a value back to the PCM computer. I thought of that which you spoke but when I saw three wires, I researched further to learn which two and found that might be like using a HiPot on a computer chip.