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Discussion Starter #1
As you can well imagine, living in Tucson, the A/C spends a lot of time running. In fact, my battery guess-o-meter said 32 miles this morning, primarily due to the heat.

My question is more curiosity than need-to-know, but I've listened to the compressor many, many times and it sounds like it is a variable speed unit. I did some searching on this forum and learned that the compressor is A/C (alternating current), 3-phase, and 300 volts. But, I did not find an answer as to whether it is multi speed or variable speed.

My home A/C compressor is multi speed, so I'm familiar with that as the two different speeds are very distinctive. The Volt, however, certainly sounds like a variable speed unit. Just curious if anyone knows for sure.

I was certainly pleased to read in my searching that the A/C compressor is considered part of the Voltec system and is covered under the powertrain warranty. Another big plus for the Volt, and for GM.
 

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HVAC System Scan Tool Data Parameters




FWIW: There is a parameter that could answer just how variable the compressor is thru the rpm speed if you have the proper GM scan tool...
 

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It's suppose to run at speeds to fit the situation, so my bet is that its a variable compressor. it certainly sounds it when it's running.
 

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I agree it's a variable speed compressor. Similar area as the OP, central CA and with the recent heat wave I can definitely hear the compressor making sounds from everything between the quietness of a refrigerator to what sounds like a jet engine from a couple hundred feet away. Certainly not a 2 or 3 speed difference.
 

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Discussion Starter #6
HVAC System Scan Tool Data Parameters

If I'm reading this right, it is inferring that the compressor motor is a single speed and a slipping clutch adjusts the actual compressor speed. Is that right? Or am I reading too much into the scan tool info?
 

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If I'm reading this right, it is inferring that the compressor motor is a single speed and a slipping clutch adjusts the actual compressor speed. Is that right? Or am I reading too much into the scan tool info?
That would be grossly inefficient and unreliable, with no benefits that I can see. As far as I know, we have a purely electric compressor that's permanently connected to a drive motor - just like your average refrigerator or home air conditioner. This means you don't need any seals on sliding shafts in the compressor, which is where they generally leak.
 

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The fact that it's a 3-phase motor sort of implies that it's variable speed. The three phases set up a rotating magnetic field that turns the rotor at that speed. The HVAC controller should contain a variable frequency DC to 3-phase-AC inverter that sets the rotation speed of the motor.

The traction drive of the Volt works the same way. The traction motor is directly connected by a 7:1 planetary-gear coupling to the drive wheels, and when you step on the accelerator you are ramping up the AC frequency delivered to the 3-phase traction motor.
 

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My 2014 gen1 compressor seemed to be a multi-speed about 6 setting or so. It is just a guess but when it changed speed it always jumped in a given amount of speed ... say 200 -300 -400 RPM.
What I am saying it was not a ramping up variable sound but more like a segmented sound as it gained speed.
 

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My 2014 gen1 compressor seemed to be a multi-speed about 6 setting or so. It is just a guess but when it changed speed it always jumped in a given amount of speed ... say 200 -300 -400 RPM.
What I am saying it was not a ramping up variable sound but more like a segmented sound as it gained speed.
Which may or may not be result of the software, just like the engine only runs at 1400, 2500, 3500, etc RPM
Doesn't mean the engine is not able to run at 1556rpm if the software commanded it.
 

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My A/C compressor has developed a new habit over the last couple of weeks. When I first start my 2014 Volt now, if the A/C is on (any setting), the compressor runs at very very high rpm for 15 to 20 seconds and then immediately drops to an imperceptible RPM and stays there. It does this same thing even when I have climate set to Eco, fan speed 1, and temp just below ambient. The first time it did this I actually thought the Engine had started for some reason. I can feel the compressor running vibration through the steering wheel and I can also hear the compressor running. By the way, when its at that high RPM if I quickly turn the A/C off, the compressor will turn off - no time delay. Prior to this new behavior I never heard or felt the A/C compressor regardless of the climate settings. Anyone else experienced this?
 

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Have you experienced less performance than usual when running the A/C? It's possible it's running at higher speeds initially to achieve an ideal pressure differential. If the refrigerant level is low or the performance of the compressor is reduced (worn, bad reed valves, etc), it may be running harder to achieve the proper pressures more quickly. Once the ideal pressures have been reached, it just has to maintain them, which would explain why the speed ramps back down to a more normal and less noisy state after a short period of time. Remember, unlike a belt driven unit that relies on engine speed and a control valve to determine the stroke size, the Volt unit is completely self-contained and uses data provided by one of the computers as well as an electric motor not unlike your refrigerator compressor to operate the refrigerant pump. It might be worth a trip to the dealer to have it inspected, especially since the compressor itself is covered under the Voltec warranty.
 

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My 2013 has always run a startup "cycle" where the pump comes on, goes through it's stages (you can hear it step up, up, up, and then down, down, down) and then either shuts off or runs at a low speed. I assumed this was normal since it always does it in warm weather.
 

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Have you experienced less performance than usual when running the A/C? It's possible it's running at higher speeds initially to achieve an ideal pressure differential. If the refrigerant level is low or the performance of the compressor is reduced (worn, bad reed valves, etc), it may be running harder to achieve the proper pressures more quickly. Once the ideal pressures have been reached, it just has to maintain them, which would explain why the speed ramps back down to a more normal and less noisy state after a short period of time. Remember, unlike a belt driven unit that relies on engine speed and a control valve to determine the stroke size, the Volt unit is completely self-contained and uses data provided by one of the computers as well as an electric motor not unlike your refrigerator compressor to operate the refrigerant pump. It might be worth a trip to the dealer to have it inspected, especially since the compressor itself is covered under the Voltec warranty.
Thanks for your thoughts. The A/C performance doesn't seem to have changed however the weather has been cooler over the last few weeks. I will take your advice and contact my dealer.
 

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My 2013 has always run a startup "cycle" where the pump comes on, goes through it's stages (you can hear it step up, up, up, and then down, down, down) and then either shuts off or runs at a low speed. I assumed this was normal since it always does it in warm weather.
Hmmm, that appears to be yet a different behavior. How long does the startup "cycle" take?
 

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On the hottest of days, mine ramps up and usually stays there. But on more normal days, it's rare that I even hear more than a slight buzzing from the compressor. I know we had a series of 100+ days here in the central valley which had the compressor running very hard making it quite noticeable. However on days when it's about 80 or so I think I hear the fans more than the compressor and it never really seems to ramp up to it's highest speed and reduce as the OP has described. It looks like we will have some cooler weather this week and I can do a test with mine to compare and report back.
 

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Hmmm, that appears to be yet a different behavior. How long does the startup "cycle" take?
Maybe 2-3 seconds total. And just FYI my A/C blows nice and cold and reliably from super-humid 70's right up to 109F (the highest we've hit this year in my area).
 

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I thought I had an AC compressor issue. My Volt is at the dealership right now for what appears to be a transmission issue. But I asked them to also check the loud A/C compressor. I was hoping it could be replaced under the Voltec warranty. Turns out it wasn't an AC compressor problem but rather the issue is with the Heater Coolant Pump (part number 13597899). They tell me that pump is not covered under the Voltec warranty. About $700 for parts and labor. Solves that mystery. Hopefully they'll get the transmission fixed soon. That of course is covered under the Voltec warranty.
 
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