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

[rybolt]

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!

View attachment Combined Temp preview.png

 

[phil0909]

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]

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]

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

 

[phil0909]

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]

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?

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

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

View attachment RYBOLT 4-18-17 Temperature Graph 73-75.png

 

[LeftieBiker]

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.

 

[michael]

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???

 

[rybolt]

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?

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.

View attachment Fan Speed Graph.png

 

[rybolt]

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!

 

[jostafew]

rybolt, nice work in logging the temperature rise and fall over time, that's some pretty solid data there. You've inspired me to get a little more serious with my observations.

I think that in a case of something subjective like "my heater makes me too hot or too cold" we're going to have to present some actual hard test results that can be replicated if we want a serious response from the service dept. I'd just always assumed that my HVAC temp control was lazy and didn't want to heat unless it really had to, I never let it run away heating long enough like you did to see just how high it would go. After seeing your test results I believe my car would do the same given the chance, and I intend to do just that only it'll be sitting in my driveway with me looking in at the thermomemter through the window hahahah

 

[devbolt]

This is a dumb question, but does this heating behavior occur at a lower set point like 72 or 70? I see that it occurred with higher temps. Perhaps there is something significant about setting a temp above 73 that triggers the problem?

I tend to put my Bolt's HVAC system in auto mode and select a temperature that gets me some air flow on my face at a comfortable temp. This may mean setting it to 70 if the outside temp is 72 or 73, or it might mean 78 if the outside temp is 80 or more. I raise or lower the temp as necessary to keep the fan at a low-ish speed unless I'm trying to rapidly cool down the cabin. I have had the temperature set to 74, but don't recall any heating issues like you have described.

When you took the car into have it looked at, it sounds like the tech followed a set procedure to make sure that the system is working properly. That usually means setting the system temp to certain values, running the system for a set amount of time, and verifying that the system is putting out the correct air temp from the vents for those temperature set points. It's possible that the particular temperature you are using falls outside of the testing procedure's parameters and they can't adequately test for the error you are having. You may have to take it back and show the service writer the exact sequence of events that produces the problem, which means pointing out that this problem only occurs when the system is set to Auto mode, temperature set point is 74, and the outside air temp is above a certain level.

I can easily see the system trying to resort to heating if the the outside air temp is a couple of degrees or more below the temperature setpoint. Every car that I've owned with an Auto mode has had behviour like that. However, the outside temp is in the 80's, and the set point is 74, then cooling should be the mode, and if it isn't doing that, then something is definitely wrong...

 

[michael]

I don't get it. The thermostat function is obviously not working as it should. The results you are showing are simply not as they should be.

If it's a design issue, everyone should be noticing the same thing and complaining as much as you are justifiably complaining. Look at the furor the seats have caused.

I don't hear a lot of thermostat complaints so yours has got to be malfunctioning. Chevy should fix it. If your dealer can't figure it out, surely another one, with smarter techs, can do so.

Ask the service manager to sit in your car for 10 minutes. If there's a problem of this magnitude it should be obvious to everyone right away.

 

[phil0909]

I did a ~35-minute test this morning, and got the same kind of results rybolt graphed. I set the Bolt's thermostat to 74, fan on Auto. Temp in the front seats rose to 86 degrees. I would not be surprised if the car got to 89 degrees as rybolt's did, if I were to continue running the climate control at 74 for a full hour, as he did. Twelve degrees and climbing is already a big enough malfunction to make the Bolt's auto temperature control worthless.

I've seen a handful of comments from various owners regarding this issue. Not enough data to say for sure, but sounds like this could be a problem for

a) all Bolts,
b) a significant number of Bolts, or perhaps
c) most or all Bolts built before a certain date (mine was December).

So, here's my question: Is there anyone who can leave their Bolt set to 74 degrees for a half hour and remain comfortable? :?:

 

[drdiesel1]

TSB released on Feb 21st. Your dealer is an idiot!


#17-NA-049: No Heat and/or Cooling, Temperature Control Setting Does Not Match What is Selected on Heater and Air Conditioning
Remote Control - (Feb 21, 2017)

 

[michael]

TSB released on Feb 21st. Your dealer is an idiot!


#17-NA-049: No Heat and/or Cooling, Temperature Control Setting Does Not Match What is Selected on Heater and Air Conditioning
Remote Control - (Feb 21, 2017)

Yep, that was my guess

 

[user 1034]

TSB released on Feb 21st. Your dealer is an idiot!


#17-NA-049: No Heat and/or Cooling, Temperature Control Setting Does Not Match What is Selected on Heater and Air Conditioning
Remote Control - (Feb 21, 2017)

Do you have a link to that somewhere perhaps? Google only shoots me to two sites, both subscription.

 

[drdiesel1]

TSB released on Feb 21st. Your dealer is an idiot!


#17-NA-049: No Heat and/or Cooling, Temperature Control Setting Does Not Match What is Selected on Heater and Air Conditioning
Remote Control - (Feb 21, 2017)

Do you have a link to that somewhere perhaps? Google only shoots me to two sites, both subscription.

Nothing free. That's from GM :mrgreen:

 

[oftheseven]

Just to chime in with my experience. We took delivery of our Bolt LT on April 14th.
Been using the HVAC with outside temperature between 77-85 degrees F.
Set to Auto @ 72 and it cooled properly. Actually, found 73 or 74 setting to be most comfortable and keeps the fan speed lower.

When outside temperature drops below 72, I usually turn off the A/C, set the temperature to Lo and fan speed at 1 to get the cool SoCal air.

Glad to see there's a TSB based on your experience.

 

[Pigwich]

Does anybody know if there's a way to check our firmware and to see if it's updated?

OR is there any chance that said firmware would come with the radio update?

I took delivery at the end of December, and while I DO notice that the Auto setting isn't quite as awesome as it was on the Spark EV, it does seem to work acceptably (not like the graphs)

Thoughts?