Title says it all. The heat will work for a few days. Then one day I turn it on and it's just cold air. It never stops working while driving it, it's always when starting a new drive. I've tried turning on Auto, tried turning off the entire heat and back on, turning off the temp button on the temperature adjuster, and even added some coolant to the heater coolant tank, which wasn't really low. Anybody else have this issue? Leary of taking it to the Stealership and them wanting to just replace everything... Nobody actually fixes anymore.
Intermittent cabin heat
- Thread starter Flyrye
- Start date
Help Support Chevy Spark EV Forum:
I've had this happen to me twice over the past few years. Not frequently enough to figure anything out about it, because so far it has always worked the next time I tried it.
Timothy Hall
Member
You must not be going very far, if you’re turning the heater on.
Infinion
Well-known member
Tl;dr I think it's just a matter of the preheating stage of cabin heating that's throwing you off on cold days. Even though it's electric, the Spark EV doesn't provide instant heat because it's designed to heat a water coolant reservoir first. If you already assumed as much, then pardon me, we might need to investigate further.
- Has it always been like this?
- How long does cold air blow at the start of each drive?
- What is the outside temperature at the start of your drive and what is your cabin climate setpoint temperature?
- While at rest, how much power does the car show it is drawing from your dash?
- Have you tried turning the temperature setpoint clockwise until the climate setpoint reads "HI"? What happens when you do this?
- While parked, under settings -> vehicle settings, do you have the auto fan speed set to high?
Because the Spark EV's heater is a PTC coolant heater, there is a significant time delay because (according to 12-2 of the owner's manual) 2.1qt / 2L of coolant is circulating through the system. If the coolant has not been warmed to a functional level yet, the blower fan will manage to blow cold air all the way through the coolant heat exchanger, and it will suck for you.
The climate controller should be programmed to keep the blower at a low fan speed, or off until the coolant temperature approaches the setpoint.
At that point, the fan speed ramps up to your auto fan speed limit that you set in my 6th question above.
There's a handy equation to figure out how long something should take to heat under ideal circumstances,
That is the specific heat formula Q = mcΔT, where Q is energy in Joules, m = mass, c = specific heat capacity, and ΔT is the initial and final temperatures.
Assuming we have an overfilled 2.5L of pure water being heated and mixed at a rate of 4kW:
The heat capacity of water is 4130 J / kg at around room temperature.
2.5L of water with a density of 1kg / L weighs 2.5kg
So the water roughly requires 2.5kg*4.130 kJ/kg = 10.325kJ per degree Celsius.
If the water is 1ºC and we want to raise it to at least 40ºC for the cabin blower to blow warm air across us,
then we are looking at a temperature difference of 40ºC - 1ºC = 39ºC
Plugging all of this information into the specific heat formula:
Q = mcΔT
= 2.5kg(4.130 kJ/kg)(40ºC-1ºC)
=402,675 J or 403kJ of energy.
Now we can find the time to heat this water using the power:
4kW = 4 kJ / second
dividing 403kJ by the power above, the energy terms cancel and we get time in seconds
403kJ / 4kW = 100 seconds
incidently, 4kW of power for 100 seconds constitutes 111 Wh of energy. (4000W * 100/3600)
So if the coolant heats to this arbitrary temperature I've chosen, it should take at least 1 minute and 40 seconds before the fan starts to blow warm air into the cabin.
edit: if you want to quickly plug in values, omni calculator has this calculator web app https://www.omnicalculator.com/physics/water-heating
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