denraweb

So I got this grand cherokee a few months ago and have been messing around with the AC a little here and there. Well today I dove deep into it checking everything that I can think of. But I still can't get the clutch to engage. So I've taken it to two separate places to have it checked. First place said they "thought" it was the AC transducer. So I replaced that, and still no dice. Second place was just a guy with an AC machine and some AC knowledge. He checked the refrigerant and verified the amount that was in it and said the clutch should engage. After looking over it for a few minutes, he concluded that there was an electrical issue somewhere. He was confident that his partner would be able to find the issue, but it would require me leaving my jeep at his house for a day or two. I got good vibes from the guy and he wouldn't even let me give him any kind of money for his time. But I'm still a little iffy on leaving my jeep with just a person and not a known shop. Any who, I'm hoping someone here can help me get the AC going as it's going to start hitting 100's soon.

So my issue is that the clutch will not engage on the compressor. I replaced the transducer with an aftermarket, as well as tried two other Mopar transducers. No dice. Jumping the clutch relay (pins 87 & 30) turns on the AC clutch and the AC blows ice cold. Swapped out different working relays to no avail. The thing I noticed (and I'm no expert) is that the FSM shows relay pins 85 & 86 seem to activate 87a which looks like that it was triggers 30 to switch 87 on. But when I pull my relay and look in there, there is no contacts in the 87a hole. So it's basically doing nothing. I don't know if that is how it's supposed to be or if there is a contact that may have broke and that's why it's no longer making contact to trigger 30 to send power to 87. With the relay in place and everything on, there is no power going to the AC clutch. But there's still power going to the relay, but it doesn't click like it's supposed to.

I pulled up the FSM and went to town checking continuity/voltage on anything I can find.

Starting with the transducer: I checked pin 1 for ground, pin 2 for 5v, and pin 3 for continuity to pin 19 on the white PCM plug. All good.
Moving on to the PCM, I checked for 12v at pin 1 on the PCM plug. I then checked continuity from pin 1 to pin 85 on the relay. Both good
I then checked pins 86 and 30 on the relay for 12v. Both showing power.
I then checked continuity from pin 87 to the A/C compressor
Moving to he automatic zone control, I checked the AZC black plug pin 9 (A/C switch signal) for power. What I noticed here is that with the AC button "ON", I was getting 2.7v out of this pin. And with the AC off, I was getting 12v.

The only thing I haven't checked yet is the body control module which the FSM shows that pin 9 on the AZC goes to the BCM.

All fuses that I can find that had anything to do with the AC, relay, clutch, or BCM were checked and all found in working order.

I know it's gonna end up being something small, but I'm just about to give up as the frustration is too much. If you have any suggestions, please let me know. Thanks!

Cherryokee

I won't claim expertise but I have successfully serviced my own in this area. FWIW, I would approach this "from the grounds up" because, based on your well-detailed notes, this smacks of control issues. You can see in the schematics that the A/C Pressure Transducer (ACPT) gets grounded through the PCM so, what's the condition of that control circuitry and the ACPT itself (NOTE: the ACPT prevents operation if the system pressure is under or over the specified pressure range). Pay close attention to the intermediate connections and their cleanliness, and find/verify the factory splices (flex, wiggle and squeeze cables at/near splices while monitoring for continuity) and always clean ground-points when/where you can. Oh yeah, and relay terminal 87a is not used in this application.

Did you know of the built-in AZC diagnostics? Here are instructions on how-to run and translate AZC diagnostic from the WJ FSM (section 24). There's a large look-up table for the resultant codes (if any) but you might find more data on-line.

ENTERING THE AZC SELF-DIAGNOSTIC MODE To enter the AZC self-diagnostic mode, perform the following: (1) Depress the A/C and Recirc buttons at the same time and hold. Rotate the left temperature control **** clockwise (CW) one detent. (2) If you continue to hold the A/C and Recirc buttons depressed, the AZC control module will perform a Segment Test of the vacuum fluorescent (VF) display. In the Segment Test you should see all of the display segments illuminate as long as both buttons are held. If a display segment fails to illuminate, the vacuum fluorescent display is faulty and the heaterA/C control must be replaced. (3) After viewing the Segment Test, release the A/C and Recirc buttons and the display will clear momentarily. If a 0 is displayed, then no faults are set in the system. Should there be any faults, either “current9 or “historical”, all fault codes will be displayed in ascending numerical sequence (note no effort is made to display fault codes in chronological order). Each fault code is displayed for one second before the next code is displayed. Once all fault codes have been displayed, the system will then repeat the fault code numbers. This will continue until the left side set temperature control is moved at least one detent position in the CW direction or the ignition is turned “OFF”. FAULT CODE TESTS Fault codes are two-digit numbers that identify a circuit that is malfunctioning. There are two different kinds of fault codes. 1. Current Fault Codes - Current means the fault is present right now. There are two types of current faults: input faults, and system faults. 2. Historical Fault Codes - Historical or stored means that the fault occurred previously, but is not present right now. A majority of historical fault codes are caused by intermittent wire harness or wire harness connector problems.

denraweb

Thank you for the info.

So for the ACPT I tested continuity to ground on pin 1 and also continuity from 1 to pin 4 on the PCM (verified plug color and wire color through FSM) and they were both good. I, however, didn't try to wiggle wires or anything while checking continuity. What if I ran a whole new wire from the PCM pin 4 to ACPT pin 1? Or maybe a new wire from PCM to ground and ACPT to ground? Do you think that would cause any issue?

Copy on the 87a. Realized that soon after that the wire was non-existent.

So when I first got the jeep, I remember doing the AZC diagnostics and I remember there were a handful of codes. Rather than actually looking into them, I just ignored it as I figured I needed to get the system service (which it needed). Now I think I need to do it again and actually pay attention. Thanks for reminding me as that may have told me the problem a long time ago lol

On a side note: I realized something today. I removed my relay and realized all the connections in the relay socket were correct. Ground at pin 85. 12v+ at pin 86. Nothing at 87 as it's the power feed to the AC clutch. 12v+ at pin 30. When I plug in the relay, pin 85 from the PCM becomes 12v+. Remove relay, it's back to ground. Seems like when it detects a complete circuit (ground 85, 12v+ at 86) it switches to 12v+. Could this indicate a bad PCM? Or could it also mean there is an issue with the wiring for the transducer and the PCM is seeing that. Causing a switch from ground to 12v+ so the circuit opens, thus not sending power to the clutch? Clutch still engages by jumping pins 30 and 87. Air gets to 40 degrees with the clutch engaged. .

Cherryokee

I'm with you on the transducer, the transducer signal and/or the transducer wiring. The ACZ diagnostic codes can/will confirm something to that effect. I think you should return to performing the ACZ diagnostics, capture and decode the multiple codes by priority (and remember that not all codes are stored and that some codes can appear to "cause" others due to relationships in the failure-chain and the way codes get prioritized). Who knows, maybe major surgery can be averted with a tiny, bitter little pill...