Has anyone experienced this?

I originally posted this on the "Should I Remove my A/C" thread but I would like to reach all members. I consider this problem to be very serious. I recently drove from Phoenix to my residence in Central AZ (about 100 miles) and experienced the rear right seat and seat back become very warm. Too warm to sit on. I noticed the A/c failing to maintain cabin temps and then a passenger in the rear noticed the hot seat. I checked the trunk and the right side was very warm. When it is 100 degrees outside - the hot seat is a big problem. This is the second time that the A/c has failed to cool properly on the same trip. The trip consists of an elevation change of nearly 5000 feet which is very draining on the engine & A/C. I learned from MSantos that the A/C indirectly cools the battery pack - so a problematic A/C leads to the hot seat.

Has anyone else experienced this? Have you taken it to the dealer. My dealer has checked out my A/C and reports that it is working properly. A pure guess by the service rep - the computer is detecting the hot engine & is turning off the A/C to conserve power. They can not duplicate this in the shop

Very frustrating.

Ed

 

Did the seat cushion as well as the seat back get equally hot? I was just curious because when I had my XM radio installed they had the back seat cushion out but not the seat back. I did not see anything under the seat cushion except metal and a few wires. The battery is supposed to be located in back of the seat back. So if they got equally hot, I would make sure you get it checked out ASAP because that has to be generating a lot of heat to travel that distance with that kind of intensity.

 

Yeah the seat cushion and the back were both hot. I just came from the dealer and they are going to look at it on Tuesday. The service rep thought it was unusual that only the right side was hot and not the whole battery pack.

 

Did you happen to check and make sure the battery vent above the middle rear seat wasn't blocked?

 

Ed, it depends on the tests that the dealer is willing to perform. Of course, it is possible for the air conditioning to perform OK is they approach the problem in the traditional sense. To fully address your issue the technician must fully understand the implementation and relationship that the climate control system has in the 06 HCH. Sadly enough Honda tecnicians are not all well versed (trained) for servicing the 06 HCH's. If you can find a dealership with technicians that have significant "trench time" then you would be in better luck.


Let me explain:

The 06 HCH has what is called a hybrid AC compressor that seamlessly works in any of 3 modes.
1- Belt driven (uses the gas engine-traditional cooling)
2- Full assist (Uses the gas engine AND the DC from the battery pack-most effective cooling)
3- Electric Only (uses DC from the battery pack - used to maintain temps and perform small temp corrections)

Now, if the technicians approach the diagnosis from a traditional perspective then they will likely focus on mode 1 only. That is it. That is not what you want. Checking refrigerant pressure, testing the system for leaks and sticking a thermometer in the vent while in stationary A/C operation in not enough.

Honda Fact: A proper diagnosis will ultimately involve opening the power control unit (IPU) and following the proper testing procedures to identify a bad temp sensor of an overheating MCM, BCM, DC-DC converter or A/C driver.

Now if a fault trully exists in the IPU module, the IPU will prevent any or all of the following:
- Motive EV assist when accellerating
- DC assist to the air conditioning compressor
- Battery pack charging (regen)

As I have stated, the reason for the high heat in the back seat is likely due to the IPU unit being unable to exhaust the heat. This is a fault condition due to any of the following:
1- Failed Fan (or failing)
2- A bad driver circuit with probably too much leakage
3- Improper or blocked cooling ducts
4- One or more bad battery cells (very unusual but not impossible).
5- Improper or damaged wiring.

I would sugest you enquire about the tests they ran. If you feel they have not gone the extent I mentioned, then I recommend you go see another dealership. Ask is they have a techician who HAS gone through the proper 06 HCH training.


Cheers;


MSantos

 

MSantos
Thank you for your very thorough reply. I will present your suggestions to my dealer.
They have been very helpful and concerned about the problem. You are correct in that they only did the basic Mode #1 test. Unfortunately I live in a small town with only one Honda dealer and so far they have been cooperative. They even suggested that they will call Corp Honda for assistance if needed. I hope they can resolve this problem.

Your suggestion of "improper or damaged wiring" might be spot on. My wife & daughter both smelled "burning wiring" - their description , but I did not detect anything other than the hot seat. Strange that only the right side was hot!
My vent behind the rear headrest is clear and apparently unblocked.

Again, thanks for your help. I bring the car into the dealer on Tuesday and will let you know how it goes.

Ed

 

Ed:

According to the service manual, the right side of the IPU contains the DC-DC converter, the MCM, the IPU fan and the A/C Compressor Driver. The Battery Module appears to be entirely on the left side (behind the left seat). So it is possible it was one of the other components of the IPU that was getting hot, not the batteries.

There is a clear airflow diagram which shows the air drawn from the rear tray is first directed on the Battery Module and then flows left to right over the other components and into the IPU Module Fan, finally exhausted in the trunk. The A/C Compressor Driver (among other components) has a heat sink to benefit from the airflow.

"The A/C Compressor Driver supplies the A/C motor compressor with switched high voltage from the IMA battery module. The A/C compressor driver receives rotation rate signals from the MCM/PCM and HVAC climate control panel through a CAN Bus to meet the driving conditions and cooling request. In case of a system failure the A/C compressor driver will communicate a DTC through the CAN Bus. The DTC is displayed through the HVAC and/or the IMA system depending on the failure."

 

Shawn;

Awesome analysis!

I believe you are dead on. Indeed, the A/C Compressor Driver is aligned with the rear right seat. My only other concern is that there is a remote chance the actual problem may be upstream the airflow before it gets to the A/C driver. In this case, the A/C Driver would be fed hot air and would simply overheat.

In any case, I hope the technicians can take it from this point.

Cheers;

MSantos

 

Shawn & MSantos thanks for your great replies. If I understand your analysis correctly then a problem with the A/C Compressor Driver is leading to a reduction of cool air that passes through the cabin & into the IPU. Or am I wrong? The failing A/C Compressor Driver would cause the Auto Climate Control to fail or degrade thus causing my increase in air temps. But - would not the IPU Fan then move the hot air out & stabilize the temp? maybe the fan is failing? Either way it looks like the problem
centers around the right side of the IPU in particular the A/C Compressor or fan. Are you suggesting that the Honda's shop analyzer should pick up the failure code?

Please correct me if I am interpreting this wrong.

One other question: during normal short drives the A/C works properly. Only on the longer uphill trip did we notice the hot seat. Would the A/C Compressor driver overload after a longer period or intermittently cut out?

Boy, do I have a lot to discuss with the service tech.

Ed

 

Ed;

A well equipped Honda hybrid technician will definitely have all the shop tools Honda recommends for proper servicing of the 06HCH. But, more importantly the knowledge and experience to "interpret" what the tools and service codes trully mean. For instance, while I agree with Shawn's excellent assessment, I would prefer to leave the door open for other equally viable "upstream" causes that could be responsible for your overheating problems. It is up to the technician to actually do the real work and that begins by looking in the right places.

Sadly, reading codes and computer screens is all some technicians do when they themselves don't know these systems well enough. As a result they request part replacements that are often wrong, overkill or require the customer to return with the vehicle many times to eventually "zero in" on the actual problem.

It is very rare to find a technician that truly knows these vehicles- in part because some service departments skimp on training efforts+resources... or simply because servicing these vehicles is very rare occurrence (small town dealerships). Some dealerships however are fixing this by ensuring that the hybrid techician actually owns and drives a hybrid !!

Anyhow, hope you get your problem addressed and resolved at the first try.

Cheers;


MSantos