CRD air conditioner problems

tsully · **Posted:** Fri Aug 16, 2019 12:05 pm

My CRD has been at the shop for a little while now after the air conditioner stopped kicking on. The initial symptoms I had a were a bit odd, it would run great for a few minutes but eventually the compressor would shut off and not come back on.

The mechanic checked for leaks, checked the pressure sensors, and was pretty sure that the compressor clutch was the culprit. After we got the compressor and clutch swapped out, the problem didn't go away though.

Now he believes the BCM is bad, seems a little odd to me though since I'm not having any other electrical issues. He did say he's seeing crazy pressure readings in the computer, but after replacing trying a new pressure sensor that didn't go away.

Is there a good way to confirm that the in-dash HVAC control unit is working properly? Anyone think it's possible that the BCM would make sense, or have suggestions on what I need to check first?

Thanks!

WWDiesel · **Posted:** Fri Aug 16, 2019 1:25 pm

tsully wrote:

My CRD has been at the shop for a little while now after the air conditioner stopped kicking on. The initial symptoms I had a were a bit odd, it would run great for a few minutes but eventually the compressor would shut off and not come back on.
The mechanic checked for leaks, checked the pressure sensors, and was pretty sure that the compressor clutch was the culprit. After we got the compressor and clutch swapped out, the problem didn't go away though.
Now he believes the BCM is bad, seems a little odd to me though since I'm not having any other electrical issues. He did say he's seeing crazy pressure readings in the computer, but after replacing trying a new pressure sensor that didn't go away.
Is there a good way to confirm that the in-dash HVAC control unit is working properly? Anyone think it's possible that the BCM would make sense, or have suggestions on what I need to check first?
Thanks!

Your signature does not tell the year of your CRD, you need to add it, it helps when trying to answer questions as 05's & 06's are different in the wiring.

If it is an 05 according to the Factory Service Manual Wiring Diagrams, both the AC sensors, Low Pressure and AC Pressure Transducer signals are routed through the Front Control Module and then on to the ECM (Engine Control Module) via the data link. It does not show the BCM being involved in the AC circuitry on a diesel. But the AC control on the dash may in fact go through the BCM and then on to the ECM??? The FSM has been proven to be wrong on some things. :banghead:

There are some grounds involved on the AC circuitry as well and a loose or bad ground could be causing your problem.
Common problem when a ground has high resistance, as it heats up the amps increase due to the poor connection and then insulates itself thereby loosing connection but can re-reconnect when it cools back off.
First thing if it were mine would be to check the ground behind the left front headlight on top of finder. Several have found problems with this ground. There is also another one under the rubber flap on the firewall cowl seal. See pictures below.

You can go to this site and pull up the Factory Service Manuals on line and study the wiring diagrams in section 8W. Be sure you are looking at the diagrams for the Diesel as the FSM has gasser diagrams as well and they are very different. You may want to share this with your mechanic?
http://www.colorado4wheel.com/manuals/Jeep/KJ/

WolverineFW · **Posted:** Fri Aug 16, 2019 1:52 pm

What in the world does crazy pressures mean? Without numbers that statement is meaningless.

The AC system in the Liberty is not very complicated electronically, there are not many electrical things to go wrong....I would say it is unlikely that electronics are the issue.

I do HVAC/R for a living. I have worked on several cars and heavy duty mobile equipment.

I think your mechanic is way off base. Sounds more like a refrigeration problem as an educated guess, likely some kind of restriction

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tsully · **Posted:** Fri Aug 16, 2019 1:59 pm

Just updated my signature, sorry about that!

I'm going to pick up the CRD this afternoon and will be getting more detailed info from the mechanic.

He recommended wiring a switch directly to the compressor so I could manually turn it on. This seems like a pretty crazy solution to me, basically throwing out the high pressure switch and any other safety checks.

Good to know the electrical system is pretty straight forward here. I lost faith in this mechanic and won't be going back, I'm just hoping I can track down what the issue is before having to find another shop to work on it!

tsully · **Posted:** Fri Aug 16, 2019 3:02 pm

Quick update - just picked up the CRD. Thank you both for such a quick reply and details this morning, hopefully the info below will be more helpful in trying to diagnose.

The computer was showing a high pressure reading of 2100, the mechanic tried 2 separate readers thinking the first was going bad. At say 350 or 400 on the high side I would expect that to be real and the cause for the compressor clutch not engaging, but at 2100 the system would have blown up...

They had evacuated the system when replacing the compressor so they knew it had no leaks and was filled properly with R-134 and oil.

At that point they believed the pressure sensor to be bad, but tried replacing it and got the same result. They did ultimately bypass the computer (he said BCM, not sure if it's actually the ECM on an '05) by grounding the AC relay and the system was working fine. The computer was still showing an extremely high reading, but with the compressor running it was blowing cold air and a manual gauge set was reading properly on both the high and low valves.

I do understand now why he thinks the computer may be to blame. He didn't find a bad ground, though I guess that'll be the first thing I check along with the wires going from the pressure sensor to the computer.

Anyone else seen a similar issue in the past, or have recommendations?

WWDiesel · **Posted:** Fri Aug 16, 2019 3:09 pm

tsully wrote:

Just updated my signature, sorry about that!
I'm going to pick up the CRD this afternoon and will be getting more detailed info from the mechanic.
He recommended wiring a switch directly to the compressor so I could manually turn it on. This seems like a pretty crazy solution to me, basically throwing out the high pressure switch and any other safety checks.
Good to know the electrical system is pretty straight forward here. I lost faith in this mechanic and won't be going back, I'm just hoping I can track down what the issue is before having to find another shop to work on it!

I certainly would not "Jury Rig" it, very wrong. That just tells you he at a loss and does not know what the problem is or how to diagnose it.
I do agree with WolverineFW, make sure all the AC pressures are correct. Too high of high side pressure will cut off the AC compressor clutch relay to protect the system.
I was assuming all of that had already been fully looked at.
If all the pressures are good, no too high readings on the high side indicating a restriction, then I would look at electrical.
Don't forget those grounds, they have caused many reported issues on these vehicles.
The wiring diagrams can be very helpful.

flash7210 · **Posted:** Fri Aug 16, 2019 3:14 pm

The compressor will turn off when the pressure sensor sees high pressure.
Since the high pressure sensor has already been replaced, then I suspect it’s a wiring problem.
Trace the wires from the sensor, looking for a broken wire or worn off insulation.
Wouldn’t hurt to check the low pressure sensor also.

WolverineFW · **Posted:** Fri Aug 16, 2019 6:41 pm

I still don't trust that your mechanic is not in over his head. None of those numbers make sense for R-134a high side pressures.

If the ECU can actually read the pressure, which on this vehicle I find somewhat unlikely since it would require a pressure transducer and not a pressure switch, then maybe the wiring is the culprit.

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Sir Sam · **Posted:** Fri Aug 16, 2019 7:49 pm

When troubleshooting issues on a flip CRD awhile back I got really weird pressure readings even with the DRBIII, i swapped sensors around and still got bad readings. Even later when everything was working the pressure numbers didn't match gauge vs DRBIII.

I don't trust the numbers the FCM(05) or BCM(06) reports via scan tool.

You got install XJ ac switches which are just high and low pressure switches to turn on and off the compressor, it would be a bit of a hack in wiring, but would be functionally safe.

If you can't figure out the other issue.

Sir Sam · **Posted:** Fri Aug 16, 2019 7:50 pm

Also, the AC clutch can be replaced without discharging the AC system. Access sucks on the KJ, but it can be done with the fan shroud off.

WolverineFW · **Posted:** Fri Aug 16, 2019 10:02 pm

Ok...my bad...after looking at the wiring diagram, the KJ does in fact have a high pressure transducer, as WWDiesel and Sir Sam pointed out. Little fancier than I expected.

So if that sensor detects high pressure, it is supposed to throw a code? Has it?

It is a standard 5 volt DC pressure transducer. Had anyone actually measured the voltage on the signal line?

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foxmiles · **Posted:** Fri Aug 16, 2019 10:44 pm

I'll second not trusting the scan tool numbers. I just checked mine out of curiosity and it oscillates between 30psi and 1700psi (roughly). I'm guessing it's mislabeled, has the wrong scaling, or something. If it was mine I'd want gauges on it to see what's happening. I'm not that familiar with the Liberty CRD specific system, but I've run into multiple things that would cause this sort of thing. Also, does it come back on by itself eventually? (does it cycle on and off or just shut off and never start again?)

1. High side too high, usually air in the system, overcharged, or insufficient cooling. Is the electric fan working? is the condenser plugged with mud or something? What are the actual pressures?
2. Low side too low, usually undercharged or a restriction like debris from a failed compressor or a stuck TXV valve.
3. ECM thinks the engine is overheating, some ECM's are smart enough to kill the A/C when they detect the engine overheating. (and some vehicles have more than one sensor, so the gauge shows everything fine while the ECU is panicking and trying to control the reactor meltdown it's seeing, but I think the Liberty only has one sensor?)
4. Relay failing, works fine until it heats up. Same thing with a cracked fuse. Looked fine, but would cut out after a while (These weren't A/C, but applicable to any issue like this)

Good luck! I hope you can figure it out!

Sir Sam · **Posted:** Fri Aug 16, 2019 11:52 pm

WolverineFW wrote:

Ok...my bad...after looking at the wiring diagram, the KJ does in fact have a high pressure transducer, as WWDiesel and Sir Sam pointed out. Little fancier than I expected.

So if that sensor detects high pressure, it is supposed to throw a code? Has it?

It is a standard 5 volt DC pressure transducer. Had anyone actually measured the voltage on the signal line?

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IIRC the DRBIII will report the sensor voltage. I should be able to look at sensor voltage, reported PSI and gauge PSI so we can correlate whats what.

That being said I only have so much time for science, gotta load up scrap metal in the AM, do the costco run, etc etc. Not high on my priorities list unless someone really needs the info.

WolverineFW · **Posted:** Sat Aug 17, 2019 4:50 am

No worries....I was thinking more about the OP having the voltage output checked since he was the one with the issues.

Sir Sam wrote:

WolverineFW wrote:

Ok...my bad...after looking at the wiring diagram, the KJ does in fact have a high pressure transducer, as WWDiesel and Sir Sam pointed out. Little fancier than I expected.

So if that sensor detects high pressure, it is supposed to throw a code? Has it?

It is a standard 5 volt DC pressure transducer. Had anyone actually measured the voltage on the signal line?

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IIRC the DRBIII will report the sensor voltage. I should be able to look at sensor voltage, reported PSI and gauge PSI so we can correlate whats what.

That being said I only have so much time for science, gotta load up scrap metal in the AM, do the costco run, etc etc. Not high on my priorities list unless someone really needs the info.

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tsully · **Posted:** Sat Aug 17, 2019 3:33 pm

Thanks for all the details and advice everyone, this forum is awesome!

I tested the relay and fuse before taking it to the mechanic, swapped each and that didn't sole the issue.

Interesting to know we can't trust the reported pressure numbers. I have it back home so I won't have easy access to check what the pressure or voltage reads are reported as.

I do have a decent gauge set though and will be testing out a few things tomorrow. I'd assume if I jump the ground to start the compressor and the high and low side pressures both make sense given ambient temps then it likely isn't a clog or functional issue in the gas system, right?

---

I was also curious about overheating, or at least the computer thinking it's overheating. I hadn't thought about it but about a month ago I glanced up and noticed the overhead thermometer read 40. I looked back right away and it was back to 87 which was correct.

I was thinking an ambient temp sensor would only come into play for automatic AC controls, but is there any chance that would be related? Maybe the computer thinks the pressure is too high because it's expecting pressures for a much colder ambient temp?

If not, would the ECM be reading the same engine temp as the coolant temp gauge? The gauge doesn't show any overheating, but that only matters if it's the same sensor being used

tsully · **Posted:** Sat Aug 17, 2019 4:11 pm

tsully wrote:

I was also curious about overheating, or at least the computer thinking it's overheating. I hadn't thought about it but about a month ago I glanced up and noticed the overhead thermometer read 40. I looked back right away and it was back to 87 which was correct.

I was thinking an ambient temp sensor would only come into play for automatic AC controls, but is there any chance that would be related? Maybe the computer thinks the pressure is too high because it's expecting pressures for a much colder ambient temp?

Well hot darn, I may be on to something here. I hadn't come across the full service manual yet (thanks for the link above!) but ran across the ambient temperature specs in there

Just went out to the CRD, turn on the electronics and the overhead is showing 78 degrees. It's 90 right now with a feels like of 105...

I pulled the ambient sensor and let it cool off inside for a few minutes. With my multimeter set to 20kΩ the reading bounces from 0.44 to 1.02 (spec range is 10k-13k at 68 degrees).

TKB4 · **Posted:** Sat Aug 17, 2019 4:27 pm

The ambient temperature reading shouldn't have anything to do with the AC in the CRD but I could be wrong not that the actual ambient temperature couldn't have anything to do with the sensors etc that do have something to do with the AC.

Yes I believe the ecm uses the same reading as the temp gauge and this is also what it goes by to go into limp mode etc if the engine overheats .

TKB4 · **Posted:** Sat Aug 17, 2019 4:29 pm

Maybe thats just why your EVIC is off. The Temp in the engine compartment with engine warmed up doesn't have that much to do with ambient temperature.

Sir Sam · **Posted:** Sat Aug 17, 2019 5:31 pm

EVIC is slow to update outside temp and the outside temp tends to get heat soaked quickly.

I don't think the ambient temp sensor has anything to do with the AC system.

tsully · **Posted:** Sat Aug 17, 2019 6:01 pm

Good to know. The service manual mentions that the low pressure switch will open if the ambient temps are below 30 degrees.

I read that as it would be factoring in the ambient temp sensor reading, but after reading it again I believe it just means that ambient temps below 30 will throw off the low pressure switch reading and cause it to open regardless of pressure

CRD air conditioner problems

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