@Fulgerite,
Excellent data! Thanks for the "crawling around" and work with the Fluke. I owe you a beer. I plan to poke around in mine and see what kind of voltage is getting to the motor. Blowers in the field are usually down about 1.5 volts from what’s measured at the battery terminals – with such high amp draw there’s a fair bit of loss in the wiring (which is why, for YEARS, GM used a high-blower relay across the board – it was the only way to get the needed power to their hungry blowers).
18.4 A, eh? That's VERY low these days -- well below the industry average, but not altogether unreasonable considering there are no rear A/C ducts in the Volt.
So here’s the problem: At 18 amps, the blower would already be one of the lowest-powered blowers (if not THE lowest) to come out of GM. That blower motor already has very little to give in terms of power and airflow (for a four-door), so adding the filter only makes a marginal HVAC system worse, and a filter restricts the airflow exactly where you need it: at the max setting, where airflow loss cannot be compensated by raising the blower speed another notch. So… this means the AC pulldown (what the layman calls cool down) times go up – by a lot. Same with heating times in the winter. To minimize the pulldown time to a steady-state, the system needs all the max blower it can get. The difference is great enough that a system running one speed below max may never reach steady state operation.
The number one way to increase A/C (or heater) performance in a car’s HVAC system is to increase the airflow. It’s what the engineers work on first to maximize in any system, and it’s also the least costly in terms of the power budget – adding A/C or heating capacity takes more e-power than adding airflow – up to a point. The ductwork, registers, and noise level are limiting factors, as is blower efficiency – if you measure airflow against amps, it’s pretty clear the blower is starting to lose efficiency if you move close to or much beyond the max setting. So, the 2A you measured will be much greater at the higher end of air flow -- to make up the difference between max and max+ filter, you'll need a lot more than 2A, and that's just part of the difference.
So here’s what happens when you restrict the airflow: You make the system work longer at higher heating or cooling settings, in two ways: (1) more amps for less airflow, and (2) higher duty cycle (more amps) on the PWM compressor / PTC heater than if they had higher airflow and reached steady-state / setpoint sooner. Out of those three loads, the blower is the smallest, the heater the largest.
Plot all these loads against time, and the net system energy used to reach steady-state (comfort or set-point) with any kind of air restriction is greater than without the restriction. Again, the best way to increase system efficiency is by increasing the airflow; the best way to harm efficiency is by restricting it.
Most of the above is moot if you don’t care about warm up or pulldown performance, of if you’re operating in a lower energy steady state – the efficiency losses are small. However, GM DOES care about heater and A/C performance at extreme temperatures, AND the impact on the Volt’s energy budget. Likewise, I agree with your math completely, provided the A/C and heater never run, and you're not trying to replace max blower airflow, but even then there’s a measurable impact on range (see below).
On an ICE vehicle, the math is the same but two key (okay, three, really) factors drop out of the equation: Power to the heater core is pretty much unlimited; power to the A/C compressor and blower are not free but pretty damn close. Answer? Put in the filter, and crank up the blower settings to compensate, go to lunch early. Done. And that’s exactly what GM has done on pretty much every other car. On the Volt, EPA testing for e-mileage and range require that the climate control be running (no cheating, boys!), so the effect on advertised and actual range factors in directly. On a cold winter day, the Volt will use as much power to heat the vehicle as it does to drive the car at a steady speed (exact speed I don’t know, but this is a public GM statement). Mess with the system by 10% energy and you now have a real impact on range.
So, while you think you’re only adding a few additional amps to the system, the rest of the HVAC system has to run longer to compensate, particularly on very hot or very cold days, where the system is already operating at it’s greatest power levels. Think of it this way: Running A/C or heat at max, vs say 75%, for even 5 or 10 minutes can put a big dent in the energy budget when compressor (or PTC) + blower loads are considered.
Let’s look at some numbers: use your 18A. Multiply x 14V* and you have 252 watts. Run that for an hour (vs off) and you have .25 kWh, or 2.5% of the Volts total range – and that’s not even considering the rest of the HVAC loads. Stretch that out to a 3-hour drive on a single charge (stop and go), and you’ve reduced the vehicles range by 7.5% by having max blower vs none – on just the FAN ONLY mode. Running the blower at full-load vs. half load over three hours will still affect the range by more than 3.5% on a three hour drive, and none of these numbers are even considering the longer A/C or heat system loads – where the power is REALLY consumed.
For those who still think that number doesn’t matter, it’s MORE THAN ENOUGH to make the difference that currently exists between the Focus EV and the Volt’s e-mileage – allowing the Ford to claim “more efficient / higher mileage than the Volt.”
So, with the Volt needing to be suitable for all-season use, the air filter didn’t make the cut. The air filter was not left out because GM doesn’t care about its customers --- they do. It’s not because they are evil – they are not. It’s not because they are incompetent – they are not. It’s because there is a fine balancing act between range (real and advertised), A/C performance, heater performance, and customer acceptance, and GM made a (mostly) engineering-based decision.
Finally: I see that Fulgerite lives in LA, land of the absolute perfect North American climate (lucky dog!). Because of that simple fact, the A/C and heater in the Volt are not taxed anywhere nearly as heavily as my beloved Michigan (ESPECIALLY the heater, the greatest load of all…), so this is one region, especially given the notoriously bad air, one would have to conclude that the filter makes outstanding good sense.
Why can’t GM offer a filter as a “factory” option? If they did, it would have to figure in their EPA testing, so we’re back to square one…
Hope this long and rambling post helps!
*14V is delivered by the battery; the blower sees a bit less. Since we’re talking about what goes into the blower system overall, we have to use 14V.