BMW A/C InOp

Jeff Owner/Technician Arizona Posted   Latest   Edited  
Unsolved
HVAC
2012 BMW 328i 2.0L (N20B20A) 8-spd (GA8HP45Z) — WBA3C1C50CF431213
A/C Compressor Doesn't Turn On

No codes. FEM/CGZ was diag'ed as the cause and replaced - still no compressor activity.

This is a clutched compressor with a control valve - both of which are controlled by the FEM/CGZ.

Live data in the FEM shows that the compressor is not commanded. IHKA shows button activity. Buttons and switches indicate normal function - A/C light is on, blower is blowing, commanded temp yields actuator movement, etc. Reprogramming/coding it had no effect. I'm not sure what PID would indicate that the command to activate the compressor is being sent by the IHKA - it has very limited data available.

Temp sensors all show ambient, give or take a few degrees.

System pressure shows as 5 BAR, which is confirmed with external gauges. Evac and recharge to verify sensor activity - filled to recommended quantity.

Applying 12v to the compressor engages it. Also sets code for control line shorted to voltage, so the FEM sees it. Same goes for control valve. IIRC, resistance across the clutch is about 8 ohms, I think the compressor valve might be less. In any event, neither are open or shorted.

There is no list of “reasons for deactivation” like GM or other brands.

0
Interesting
Tomasz Diagnostician
Ontario
Tomasz
 

If you using ISTA, perhaps you could create test plan for AC inop.

0
Ð Awarded
Jeff Owner/Technician
Arizona
Jeff
 

Did that. It has me check temps and pressures. Tells me to turn on the system. Does it light up? Then its working normally! lol The next step after answering the question “is it working” with a firm “NO” is to go back to the top of the test plan. I don't normally dig out ISTA/D or ISTA/P unless I have to program something that my Autel might blow up otherwise (like the FEM in this car).

0
Ð Awarded
Tomasz Diagnostician
Ontario
Tomasz
 

You don’t have any other faults, anywhere else? cooling fan operational? What’s the pressure sensor reading when was empty? How about voltage drop on clutch wires?

0
Ð Awarded
Jeff Owner/Technician
Arizona
Jeff
 

No DTCs anywhere. Car is fault-free (amazing for a BMW). It is a very low mile vehicle. Cooling fans work - idled the car for several hours. Pressure sensor reads zero when empty. Matches a gauge set when charging. The FEM/CGZ is new. When commanding the clutch or flow solenoid, they function and show battery/alt voltage. There is almost no drop when using the Power Probe. Resistances are…

0
Ð Awarded
Tomasz Diagnostician
Ontario
Tomasz
 

Don’t think pressure sensor should be at 0v when empty. take a closer look at it. you should also have auc sensor that might cause the issue.

0
Ð Awarded
Rob Technician
North Carolina
Rob
 

Is your outside temperature sensor working. BMW uses it as part of their climate control. If it’s reading too hoof or low it blocks the A/C compressor from activating.

+1
Ð Awarded
Jeff Owner/Technician
Arizona
Jeff
   

Yep! As noted in the original post - all of the sensors (2 sensors outside, 4 sensors inside, evaporator, IAT, ECT, etc) are reflecting reality. I tested them with a heat gun as well.

0
Ð Awarded
Bruce Owner/Technician
California
Bruce
 

Had one that the blower final stage resistor was keeping the compressor from engaging Had no faults

0
Ð Awarded
Jeff Owner/Technician
Arizona
Jeff
   

All blower positions work incrementally in both directions from off to MAX. All modes are functional as well. Blower “resistor” is a driver module over a local network, anyway.

0
Ð Awarded
Bruce Owner/Technician
California
Bruce
 

That’s what I thought, until I found last shop replaced resistor, and that’s when compressor stopped, it had all speeds!

+1
Ð Awarded
Justin Mechanic
Tennessee
Justin
   

Based on what you’ve said, I dont think the IHKA is signaling the FEM to activate the compressor, despite having all the needed inputs to do so. It sends this signal over the K-bus, so other than by looking at status requests, it’s hard to know if the IHKA is sending this request, like you said. Perhaps a battery reset might be something to try.

0
Ð Awarded
Jeff Owner/Technician
Arizona
Jeff
 

All temp sensors - vent discharge, ambient, outside and evaporator all show ambient temperature (about 20॰C), give or take a degree or two.

0
Ð Awarded
Justin Mechanic
Tennessee
Justin
   

Is there a PID in the IHKA for ”desired temperature“. In other words, I know you’ve got the temperature dial turned to full cold probably, but is the IHKA actually seeing that? Scope the K-bus at the connector on the IHKA and see if you can correlate a data packet with pressing the A/C button. Might be difficult to do.

0
Ð Awarded
Gilles Technician
Quebec
Gilles
 

Is your solenoid operational takes the resistance compared with the specifications it may be an open circuit

0
Ð Awarded
Zanozin Engineer
Ukraine
Zanozin
 

Hi mate. Check operation of condenser Fan motor in front of radiator , try to activate it from ISTA or another OEM scanner, as IHKA required valid operation status of this fan to activate the compressor clutch. It’s quite often problem on this system, check presence of Voltage on fan connector before condemn the fan motor.

0
Ð Awarded
Jeff Owner/Technician
Arizona
Jeff
 

I have already verified the fan function - both by watching it work after a long drive/idle and through tool activation.

0
Ð Awarded
Mike Mobile Technician
South Carolina
Mike
 

I ran into a BMW a while back that had no A/C after a programming event. I fought it for an hour and then it just started working. I later read someone with a similar issue stating it' common for the AC not to turn on right away with no indication of why after programming. If that wasn't the original Issue I might let it go to sleep for an hour and then drive it and see what happens.

0
Ð Awarded
Jeff Owner/Technician
Arizona
Jeff
   

It came in in/op - no programming at that point. Programming was only after swapping out the FEM/CGZ. It was then driven and then left to idle for several hours.

0
Ð Awarded
Matthew Owner/Technician
Georgia
Matthew
 

Perform the compressor run-in in ISTA and see what happens.

0
Ð Awarded
Jeff Owner/Technician
Arizona
Jeff
   

Tried that. No change. Also ran both protection routines. The compressor never engaged.

0
Ð Awarded
Boyd Technical Support Specialist
Georgia
Boyd
 

Try recoding the cluster, JBE, and FEM.

+1
Ð Awarded
Interesting
Justin Mechanic
Tennessee
Justin
 

The IHKA control module is separate from the control panel. The module is shown to be actually located on the hvac unit housing. The control panel sends the command to the IHKA module over a LIN bus. They also show to pass through the audio control panel before going on to the IHKA module. So maybe there is a problem between the control panel and the actual IHKA module.

0
Ð Awarded
Zanozin Engineer
Ukraine
Zanozin
   

check in DME status of compressor shut off/on signal request if it’s possible,when you activate in through ISTA, to see if IHKA can communicate with DME​.​What about all prerequisite: evaporator temperature should be more then 4 degrees,engine temperature less then 120 degrees, ambient temperature more than -1 degree , condenser fan operation,engine speed more than 600rpm , refrigerant pressure…

0
Ð Awarded
Bryan Owner/Technician
Washington
Bryan
 

The AUC sensor can deny the request to the FEM.

0
Ð Awarded
Justin Mechanic
Tennessee
Justin
   

Remove the AC/ Audio control panel from the dash and check connector “S136*B” pin 2 which is a blue and white wire. That should be the Lin bus going to the IHKA control unit. Maybe put your scope there and press the AC button and see what you get.

0
Ð Awarded
Bob Service Manager
Virginia
Bob
 

Like Bruce said, blower resistor. Doesn't matter that blower works on all speeds if someone replaced it with non OE. The only aftermarket that works properly is Valeo

0
Ð Awarded
Jeff Owner/Technician
Arizona
Jeff
 

Blower resistor and the blower motor were replaced before I got there with an oem Valeo part. Verified.

0
Ð Awarded
Bruce Owner/Technician
California
Bruce
 

Just make sure that the problem didn't start after replacement of those parts.

0
Ð Awarded
Jeff Owner/Technician
Arizona
Jeff
 

Really no way to verify that. It came in, apparently, with no A/C and no blower function. So, they replaced the blower motor and final stage module ("resistor") with dealer parts and it still had no compressor function. So they called an FEM/CGZ.

0
Ð Awarded
Bruce Owner/Technician
California
Bruce
 

If it was me, I would try a different resistor, just to rule it out.

+1
Ð Awarded
Nick Owner
California
Nick
 

I second what Bruce and Bob have said. We had a similar issue with a 2013 328i. We ran through all the tests you have without finding a cause for the compressor not activating. We were ready to send it to the dealer when we decided to try throwing a new Valeo resistor in it. The compressor magically started working as soon as we did that. Original one worked normal except for the compressor…

+1
Ð Awarded
Interesting