Volt back at the dealer again

[mikeyd810]

Well only had the car two weeks now and it's been in the service department each Friday since. Keep getting a CEL that points to low pressure in the AC system. They can't seem to trace down where it's leaking even after using dye in the refrigerant. Starting to get a little bit frustrated I can't enjoy my car right now.

Off to pickup a loaner for the weekend...

[CarZin]

Wow. I didnt know they monitored the AC pressure. I guess we'll all know when the AC is going out. This thing has a ridiculous amounts of sensors (to go bad and need replacing)

[mtndrew1]

If the Volt's A/C system wasn't working properly then the battery's TMS would also be down, leading to potentially devastating consequences. No surprise that this defect popped the CEL.

-Drew

[bonaire]

How does that AC influence and/or work with the battery TMS? TMS uses coolant that heats up and goes through its own radiator.

[mtndrew1]

If I'm not mistaken there's a chiller powered by the a/c that cools the pack. It's integrated in such a manner that sometimes the car sends chilled air to the cabin when the TMS is active even if the driver hasn't selected a/c for the cabin climate control.

-Drew

[DonC]

The good thing about the sensors is that usually they fail immediately or they don't fail for a long time. But I agree with CarZin that the car seems to have more than the average number of sensors.

If I'm not mistaken there's a chiller powered by the a/c that cools the pack. It's integrated in such a manner that sometimes the car sends chilled air to the cabin when the TMS is active even if the driver hasn't selected a/c for the cabin climate control.

Drew, I think you're right that there is some connection between the cabin evaporator and the battery chiller. The AC condensor is routed through both the battery chiller and the cabin evaporator. If the Condensor it turned on for the battery chiller the cabin evaporator will take advantage of that. http://gm-volt.com/2010/12/09/the-ch...ems-explained/ But the evaporator is not directly connected to the chiller.

I'd agree with bonaire that if the cabin evaporator went down it shouldn't effect the battery chiller and the TMS. On the other hand if the AC condensor was on the fritz then this would effect the TMS.

[bonaire]

A123 EXT please (ie. cells which apparently won't need TMS and would make the pack cooling a lot easier and fewer sensors, etc.) Currently, if it is 90*F ambient outside, the Volt TMS still wants to get the pack down to 70 or so *F. This is the good thing about the TMS - it keeps the LG Chem cells (which need a TMS for longevity) in the right temperature range in the hotter weather.

Did you guys see the specs on the Honda Fit EV? Those are entirely different Lithium cells (2.4V and 10C charging - and air-cooling). Batteries are going to go through a lot of changes and I think one of the major goals is to get EVs out there without TMS. Those with leases may be in a good position to get into them in 2015+ when the next gen Volts (and others) start to come online.

[Bzzzt]

The good thing about the sensors is that usually they fail immediately or they don't fail for a long time. But I agree with CarZin that the car seems to have more than the average number of sensors.

Drew, I think you're right that there is some connection between the cabin evaporator and the battery chiller. The AC condensor is routed through both the battery chiller and the cabin evaporator. If the Condensor it turned on for the battery chiller the cabin evaporator will take advantage of that. http://gm-volt.com/2010/12/09/the-ch...ems-explained/ But the evaporator is not directly connected to the chiller.

I'd agree with bonaire that if the cabin evaporator went down it shouldn't effect the battery chiller and the TMS. On the other hand if the AC condensor was on the fritz then this would effect the TMS.

The condenser is in front of the radiator, its where the freon is cooled after its compressed. Heat is radiated from the condenser to the outside air.
The evaporators are fed compressed freon thru the expansion valve, and is where the freon evaporates, resulting in cooling.
There are two evaporators, one for the cabin air, one for the battery coolant loop. The chiller is an evaporator.

Loss of freon pressure would cause a lack of cooling in both the cabin and the battery system.

[mikeyd810]

From what I could gather it sounds like this system is separate from the Battery TMS. I went to pickup my car today and they said after using the dye in the refrigerant they found a light leak on one of the seals near the AC compressor, this was after the called the Volt Technical Team. Unfortunately the service manager really didn't know for sure if this would solve the problem, gave it a 50/50 chance with his confidence level.

Now the kicker, as I get in to my Volt and power it on I notice the red battery light on. I called over the service adviser right away and turned it off and back on and bam comes up the service charging system notice. My Volt now gets a longer stay at the dealership. I'm really trying to be understanding with the newness of the car and its technology but after only having my car in my possession thirteen days out of the nineteen I've owned it I'm fast getting frustrated.

So wait and see at this point, I won't get it back till next Wednesday since I'll be out of town at this point.

[saghost]

From what I could gather it sounds like this system is separate from the Battery TMS. I went to pickup my car today and they said after using the dye in the refrigerant they found a light leak on one of the seals near the AC compressor, this was after the called the Volt Technical Team. Unfortunately the service manager really didn't know for sure if this would solve the problem, gave it a 50/50 chance with his confidence level.

It is, and it isn't. The battery TMS is a dexcool coolant loop, with it's own radiator and pump. At the front of the battery enclosure it has a 1.8kW electric heater for when ambient temperatures are to low - and there's also a chiller (an evaporator that transfers to water instead of air) that's hooked into the same A/C loop as cabin cooling, which is what the car uses to hold the battery below ambient when ambient temperatures are too hot.

Loss of refrigerant or a compressor failure of the A/C system would prevent the TMS from keeping the battery lower than ambient temperatures in hot weather - and thus compromise the battery management strategy and potentially lead to accelerated degradation similar to what Leafs are experiencing in PHX and Texas. So it's related and I'm not at all surprised that GM put sensors in to monitor it.