rybolt
Posts: 30
Joined: Fri Mar 03, 2017 1:12 am

Is HVAC burning you up too? Chevy says "nothing wrong"

Fri Apr 21, 2017 1:30 am

Now that the weather is starting to warm up a bit, I've discovered that the "A/C Auto" mode on my Bolt's HVAC system has some pretty radical ideas about what the temperature control should do. In fact, I suspect that ALL of our Bolt EVs may be afflicted.

I borrowed a temperature logger from work to try and figure out what was going on and captured cabin temperatures up into the high 90ºs after letting the car run at 74º in "auto" for an hour.

It's important to note: The air conditioning unit itself works fine mechanically. How do I know? Because by setting the controls to 70º, the cabin temperature confidently dropped until settling into the low 60s. Wait, what? I think my Bolt's thermostat is drunk.

As far as my dealer is concerned, the heater is heating just fine and the A/C is cooling just dandy, so it is the assessment of their "factory-trained technician" that everything is working as designed. They kept my car for three days before arriving at this conclusion, so at least they were good and thorough about putting the system through their prescribed tests. (As an aside: If I hadn't already come to appreciate the brilliant engineering of the Bolt's electric drive, those three days I spent in the combustion-engine loaner they set me up with certainly convinced me!)

This might be a bigger deal than my Bolt alone merely experiencing a chance defect in a piece of 1880s tech. I tried the same experiment with my coworker's vehicle (in exchange for topping off his battery) and observed the same result! Uh-oh.

Chevrolet Customer Assistance, who had graciously set up my dealer appointment, doesn't appear to have any interest in following through on the possibility that our entire model of car may have shipped with a malfunctioning thermostat. They claim that nobody else has had this problem, so based on the report from my dealer's "factory trained technician" that my car is working as designed, there's no need for them to investigate any further. Even after escalating to a manager level, their position is that there's nothing wrong with my Bolt's HVAC, or anyone else's.

So, forum members: Set your thermostats to 74º (or 75º) and turn Auto mode on, and see what happens!

Combined Temp preview.png
Graphs from two different temperature tests showing runaway heating and runaway cooling
Combined Temp preview.png (94.44 KiB) Viewed 4669 times


RYBOLT 4-20-17 Temperature Photo 1545.jpeg
Testing at 74º on the console, with an "outside" upper level (covered) garage temperature of 82º (cabin temp rose from 81º to 91º)
RYBOLT 4-20-17 Temperature Photo 1545.jpeg (157.04 KiB) Viewed 4938 times


RYBOLT 4-18-17 Temperature Photo 0835.JPG
Testing at 70º on the console, with an "outside" lower-level garage temperature of 66º (cabin temp fell from 76º to 66º)
RYBOLT 4-18-17 Temperature Photo 0835.JPG (148 KiB) Viewed 4938 times
Last edited by rybolt on Mon Apr 24, 2017 3:36 am, edited 10 times in total.

phil0909
Posts: 269
Joined: Thu Jan 05, 2017 7:25 pm

Re: Is HVAC burning you up too? Chevy says "nothing wrong"

Fri Apr 21, 2017 4:55 am

I noticed the drunken thermostat as soon as I got my Bolt, in the winter. I needed to set the temp to ~76 or higher to get any heat at all, at first. But after a few minutes, without changing the temp setting, temperature would climb steadily up. So, to compensate, I needed to turn the temp setting down 2 degrees every few minutes.

Now that the weather is a little warmer, I sometimes use AC. I don't even bother trying to set a temperature - I just set the AC to 'Cold", and run it till the car gets too cold, at which point I turn it off for a while. Kind of annoying, and I don't know why the Bolts have this problem. My old car was a 1998 model, and thermostat and temperature sensors worked fine - I set the temperature at 68 degrees the day I bought the car, and never had to change it in 19 years.

I have zero expectation that this will ever be fixed, so I just control the AC manually and don't worry about it.

RyanZ
Posts: 18
Joined: Fri Mar 17, 2017 9:52 pm

Re: Is HVAC burning you up too? Chevy says "nothing wrong"

Fri Apr 21, 2017 5:08 am

This is just a guess as I don't know where the Bolt's temperate sensor is, but my old Subaru Forester had a very similar problem. The issue was that the car used the motion of air passing though the duct work to suck in a small amount of air past a sensor on a perpendicular tube (the Bernoulli Effect).

It worked great when the fan was on medium or high, but when it was on low there wasn't enough suction to get an accurate reading. The effect was the temperature got close once then started swinging wildly around the set point. Snapping off the tube and bolting a small 25mm 'pc' fan onto the opening fixed it.

Is it possible for you to leave the fans on high while the rest of the system is on auto to see if that's it?

Fulmine
Posts: 35
Joined: Wed Jan 18, 2017 3:36 pm

Re: Is HVAC burning you up too? Chevy says "nothing wrong"

Fri Apr 21, 2017 3:00 pm

I have noticed that fiddling with the fan speed helps a lot.

phil0909
Posts: 269
Joined: Thu Jan 05, 2017 7:25 pm

Re: Is HVAC burning you up too? Chevy says "nothing wrong"

Fri Apr 21, 2017 5:31 pm

Fulmine wrote:I have noticed that fiddling with the fan speed helps a lot.


Not for me. Anything higher than speed setting 1 or 2 is noisy and uncomfortable.

rybolt
Posts: 30
Joined: Fri Mar 03, 2017 1:12 am

Re: Is HVAC burning you up too? Chevy says "nothing wrong"

Fri Apr 21, 2017 5:44 pm

RyanZ wrote:Is it possible for you to leave the fans on high while the rest of the system is on auto to see if that's it?
Fulmine wrote:I have noticed that fiddling with the fan speed helps a lot.

Good question / suggestion! I don't know if overriding the auto-fan speed will make a difference or not, but I can test it this weekend and see if there's a change.


Meanwhile, here are the full screenshots of the temperature graphs I added to my original post, showing an extended period with "Heat A/C Auto" set to 70º, 73º, and 75º

RYBOLT 4-18-17 Temperature Graph 70.png
RYBOLT 4-18-17 Temperature Graph 70.png (98.57 KiB) Viewed 4811 times
(The uptick at the very end is when I got back in the car to record the results)

RYBOLT 4-18-17 Temperature Graph 73-75.png
RYBOLT 4-18-17 Temperature Graph 73-75.png (113.24 KiB) Viewed 4811 times
Last edited by rybolt on Sun Apr 23, 2017 9:55 pm, edited 2 times in total.

LeftieBiker
Posts: 793
Joined: Tue Jan 10, 2017 7:13 am

Re: Is HVAC burning you up too? Chevy says "nothing wrong"

Fri Apr 21, 2017 8:04 pm

In every car I've driven with climate control (all of about four, I think) pressing AUTO causes the fan to run on High until the desired temperature is reached. If the Bolt fan stays on a low setting, this is definitely part of the problem.
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2009 Vectrix VX-1 with 18 Leaf modules.

michael
Posts: 651
Joined: Thu Jan 29, 2015 10:13 pm

Re: Is HVAC burning you up too? Chevy says "nothing wrong"

Fri Apr 21, 2017 8:14 pm

It seems pretty clear there is a malfunction. The question is whether it's a design defect (happens to everyone) or yours is broken.

I've had several Chevys and the thermostat works decently well, so they seem to know how to make one work.

Try another dealer maybe???
2013 Ford Focus Electric 51000 miles in 34 months, returned
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rybolt
Posts: 30
Joined: Fri Mar 03, 2017 1:12 am

Re: Is HVAC burning you up too? Chevy says "nothing wrong"

Mon Apr 24, 2017 2:06 am

RyanZ wrote:Is it possible for you to leave the fans on high while the rest of the system is on auto to see if that's it?
Fulmine wrote:I have noticed that fiddling with the fan speed helps a lot.

I did three tests today. 74º F for an hour with the fan speed at 8 (highest), 1 (lowest), and off. I tried to cool the car down as best I could between tests but, as you can see, I just couldn't get things to "reset" completely. Still, I think the results are important, as they show that fan speed isn't really a factor when it comes to Drunk Thermostat Syndrome.

Fan Speed Graph.png
74º F for an hour at highest fan speed, lowest fan speed, and with the vehicle off
Fan Speed Graph.png (169.67 KiB) Viewed 4659 times


Fan Speed Temperature photo.JPG
Measuring the cabin temperature at the end of the first test - 91.6º F in the cabin and 103º F still pouring out the vents!
Fan Speed Temperature photo.JPG (149.75 KiB) Viewed 4660 times


Fan Speed airing out.JPG
This is how I aired out my Bolt between tests (laser temperature guns are FUN!)
Fan Speed airing out.JPG (163.79 KiB) Viewed 4660 times

rybolt
Posts: 30
Joined: Fri Mar 03, 2017 1:12 am

Re: Is HVAC burning you up too? Chevy says "nothing wrong"

Mon Apr 24, 2017 9:07 pm

For those who aren't sick of graphs yet, here's my Bolt's cabin temperature heating up (and up and up) during a drive on a cool but sunny Southern California morning, with the climate control set to 74º F. It took a lot of commitment (and sweat) not to change it toward the end!

RYBOLT 4-16-17 Temperature Graph.jpg
Downtown L.A. to Fillmore, CA (Climate setting 74º F, Outside air 64º-71º F)
RYBOLT 4-16-17 Temperature Graph.jpg (166.71 KiB) Viewed 4593 times

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