Using the heat when it's cold... mpg drain?
 

The title says it all... I know AC is a huge drain on mileage, but does using the heat work the same way? I'm admittedly clueless when it comes to cars; I just bring it to the oil change place every 3,000 miles and have them do what's in the Toyota maintenance booklet once I hit a maintenance interval. :p

The heater doesn't activate the a/c compressor, which is the big power drainer. Using the heat setting especially with low fan settings should minimally impact fe- probably at an undetectable level.

I tend to like to regulate temps with the heat control on the lowest blower setting. I know some people, particularly women, like to blast that freekin fan wide open at every opportunity. The fan draws juice which must be generated, indirectly, by the engine.

There has been debate about whether it's better to leave the heat control on cold until the car warms up, or put the heat control on hot right away. Conclusion is that if the blower fan isn't causing the mass extraction of heat from the heater core, the difference is so minor as to be inconsequential. I leave the control on hot right off, with blower off, on the defrost setting, and wait until I can feel some warmth trickling out with my bare hand before bumping up the fan setting a notch or two.

All that breathing tends to fog things up so it helps to either have the window cracked open a bit or only close the door to first catch until the heat starts flowing.

Re: using the defroster: the defrost setting will activate that a/c compressor on most cars so that could be a similar loss to using a/c. But when you need it, you need it.

It helps to clear snow from the air inlet at the cowl- reduces moisture and thus fogging on the windshield. On that note, stomping the snow off your boots and shaking the floormats clean can help reduce humidity in the car too.

The gung-ho can disconnect the a/c clutch for compressor-less defrost operation. I guess I'm gung-ho as all my cars are like that. Well, really it's because the a/c is broken on all of them. That eliminates compressor operational losses. I still haven't bypassed the comps with shorter belts.

And... unless you really, seriously do fall under the severe service guidelines, you are wasting oil and money by changing it that often. It should be able to go more than twice that far between changes.

With a full grille block on a hot summer day, just moving the temperature control dial to Hot will measurably drop the coolant temperature. This is with the fan turned OFF. Based on that, I conclude that it cools the engine even with no fan blowing, so I leave it on Cold until it's fully warmed up.

With a 10 mile commute, a tiny aluminum engine, and heavy use of EOC, that's pretty much never. I practice dwg (driving with gloves).

I guess I am one of the "hard core" also as I have disconnected my a/c compressor electrical connector. I like to run my defroster or the setting where the air comes out of the defroster and at floor level. What I did not know was the radiator cooling fan comes on whenever the a/c is supposed to come on. I noticed at night how my lights would dim slightly and you could feel the load on the engine whenever you selected the defroster. The rad fan fuse is 40 amps!:eek: I looked in the wiring diagram for my car and found that by pulling the a/c fuse (15 amp) the fan no longer kicks on when I select defrost.:thumbup: You may want to check yours.

Personally I hate that feature. If they give you a button to turn on the a/c when ever I want, they shouldn't feel the need to have it come on automatically. Maybe on 100% defrost only.

In my Mitsubishi I can turn the knob a few clicks past heater toward heater/defrost before the A/C will activate. I figure it's cheaper to run the fan faster than the a/c compressor. I was able to figure this out by turning on the reciculator feature & turned the selector knob until the recirculate light went out. On defrost it won't let me have the recirculate on, to try to get rid of the humidity.

Don

Well, I do have an AC button... if I leave that turned off, would the compressor still activate with the defroster on? I don't see why the AC compressor would need to be on for the defroster to work, given that it's called an AC compressor, but then again, I don't even know what its function is.

It acts as a dehumidifier to aid in defogging the windshield. The a/c button allows you to turn it on when "You" want. The car will turn it on when "It" wants to.

In the winter here it gets pretty humid so every once in a while I put my dehumidifier in the van to get the accumulated moisture out. That way I don't have to use the fan as much.

You can have a block heater or coolant heater installed that plugs into a 110V outlet that warms up the engine. With a timer you can set it to warm up the car before you get up in the morning so you have instant heat. This is good for FE as well because the engine gets up to operating temperature much quicker. I have one that I use year round because I have a short commute.

Okay, so when it gets cold out and you get in the car and the windshield is all fogged up, the only way to get the condensation to go away is to run the defroster and heat, right? Just trying to find out if there's a way I can do this without killing my FE. (I had to run the defroster and heat for an hour tonight cause it actually snowed here... that never happens in October!) :(

I've been known to wipe it with a rag too. There are "anti-fog" wipes and cleaners but I haven't tried them.

Try throwing an insulating blanket over the window over night. Try it with a regular blanket if you don't have the bubble wrap with foil type. To reduce condensation you have to either reduce the moisture in your car or warm up the glass a bit so the moisture does not condensate at all. Think of it like double glazing only the insulating layer is a blanket not another layer of glass. This also works to keep off frost. I had good success with keeping off frost with just a foil blanket held on with some rare earth magnets.

I think many cars use resistors in the blower circuit to reduce the speed of the blower. If this is the case then the blower will use the same amount of electricity on all settings. On the slower speeds you will just have electric heat. The resistors are usually in the heater duct.

I've measured my blower, and the power draw is proportional to the speed setting - low speed uses less than high speed. Sitting with the engine off, reading battery voltage, and each higher setting drops the voltage another 0.1. Back to a lower setting and that 0.1 comes back. I'm not sure about the why or how, though.

Volts - Fan setting
12.2 - Off
12.1 - 1
12.0 - 2
11.9 - 3
11.8 - 4

If you are just reading voltage then you haven't measured the power used. You have to measure amperage too. Amps X Volts = Watts (power)

To be technical, yes. However, when you draw more current from a lead-acid battery, it's voltage drops. This is an indirect and easy way to compare one setting against another. I don't know how much current it's drawing. I do know that the fan on setting 3 draws more than on setting 2. That's my point, that there is a difference.

Pale is correct. Darin tested this a while ago.

From: http://ecomodder.com/forum/showthrea...olts-8908.html


Since I run with my alternator disabled, and now that it is fairly cold in the morning, I'm still very careful about using the fan. As Darin found out, his fan can consume more power than his car requires to run the engine! That, plus the addition of using headlights is a large drain to the battery. If I can avoid it, I don't use it.

Resistors don't work that way. They're not "burning up" the extra electricity, they're more like valves that just let a certain amount through.

The resistors used in heater circuits are coils of resistance wire which are placed in the heater duct to dissipate the heat they generate and eliminate the possibility of melting/burning something. (like fingers)

What?

Since current is constant through the entire series circuit, the resistors are in fact "burning up" wattage, they're burning up voltage to be specific.

A resistor is not a transistor.

Ok I had to check, to easy...
I just measured the blower draw on my Jeep, same power on all low and med more on the high speed, the heating element it uses for speed control is right by the blower.

It was pulling about 5.5 amps low and medium... Jumped to 7.5 on high...

Dave

Sure. I was trying to give a simplistic explanation, without invoking Kirchoff's Law &c. But try a simple experiment: take a 12-volt battery, and connect a piece of copper wire (low resistance) between the terminals. Lots of current flow, heat, sparks, etc - and in particular energy "burned up". Now put a piece of wood (very high resistance) between the terminals. Does the wood start to smoke & catch fire from all the energy it's burning up? No, because current isn't flowing because of the resistance.

ETA: Or consider the transistor: it's a device that's switchable between two states, high and low resistance. When it's in the high resistance state, is it "burning up" the power that's not flowing through it?

Try your experiment with a piece of #24 or finer wire but be careful because it it going to get HOT!!!!!!!!
The reason a piece of wood won't get hot is that there is no current flowing through it to generate any.
Why do you think they mount power transistors on a heat sink?
Why is your CPU mounted on a heat sink with a fan?

Test your car's blower fan, and report back with real results.

Yes, that's exactly my point. You don't have as much current flowing through a resistor (V = IR, remember?), so less energy flow, so no heat. But don't take my word for it, look at a basic electric/electronics text, or put a temperature probe on one of those resistors that are supposed to be turning energy into heat.

Oh, and another question for thought: how come the wires in your toaster or electric heater - or indeed, the tungsten filament in an incandescent light bulb - are made of metal, which has a low resistance? Just for the heck of it, I dug out a few old incandescent bulbs, and measured their resistance: 40 W = 30 ohms, 60 W = 17 ohms, 75 W = 13 ohms. Not high resistance at all (though of course it increases with temperature), yet lots of heat.

Remember the transistor is a semiconductor. It's generating heat when current is flowing, and that's when it's in its lower resistance start.

Exactly. The wire wound resistors in my car are 1.3, .62 and .33 ohms each. Not mega-ohms or kilo-ohms, just ohms. Very low resistance, generate heat. That is why they are typically located in the duct to aid in cooling. Low setting routes through all three resistors, med low through the .62 and .33 only, med high through the .33 only, and high straight to the blower motor.

And those measured values change when current is flowing through them. The resistance will be less without current flow - so using ohms law will not work by calculating it.

Learned something new relevant to the original question of this thread:

BMW engineers say:

So... with some diesels, using the heat can impose a significant MPG penalty... because of a dedicated electric heating element.

I have read anecdotal stories about the smart fortwo diesel that was sold in Canada having insufficient cabin heat in really cold (think -20 C and below) conditions.

The Toyota Echo sold here also had a beefy electrically heated element in the defrost circuit so you could start to clear the front glass before the engine warmed up. Not sure if it's still offered on the Yaris or other cars.

I have to say in the depths of winter, I am sometimes very thankful for the ~20% inefficiency of my gasoline engine and all the waste heat it produces!

jamesqf is right about resistance and electrical usage.
I remember thinking the same thing though when I was in high school about resistors - they cause a voltage drop and do warm up, so they must waste energy. Luckily this is not the case, or at least they don't waste more than about 1% of what I thought back then....
The block of wood DOES conduct some electricity. It's inversely proportional to its resistance, so it is essentially none.... just like you will conduct electricity at 12V. Not enough to feel it usually, but some.
Just think about how hot those resistors would have to get if they took a high speed fan and took enough energy away from it to make it run 1/3 as fast.... lots of E would transfer to a fiery resistor really quick. Luckily they just get warm.

And just think what having what would be in effect an electric heating coil in your ductwork, when you're using the fan for A/C :-)

Which is exactly what they are! Have you even seen what any of these look like! Wire resistors, nicrome wire. Lot of heat, low resistance, high current flow. Google is your friend. All kinds of reports of melting and even a few fires.

Here is one from a 1996 Ford Escort:

http://www.2carpros.com/forum/automo...4_274137_1.jpg

My Honda one looks very similar to that. Still, the fan draws significantly less power on low fan speed than on high speed. It *must* be resisting / restricting current flow, not just burning up voltage.

Nowadays, it is common to use electronics to control motor speed, which is very efficient. One easy way to tell is by the presence of a digital control. If it uses buttons or a knob that will turn continuously, it is electronic. PWM is very easy to implement, but inverter drive is the most efficient.

It should be very easy to make a retrofit PWM fan controller. Just a potentiometer varying the duty cycle of an oscillator (~15kHz for high efficiency) and then use a MOSFET and Schottky diode as the motor control stage.

Beware that if you set the fan speed very low with the A/C running, it can freeze the coil and possibly slug the compressor. Therefore, add a comparator to lock out the A/C compressor below the original low speed. One LM339 can operate as the oscillator, PWM comparator, and A/C lockout comparator. Add some resistors and capacitors and a few transistors for the MOSFET driver and A/C lockout relay driver.

It absolutely IS resisting current flow. A resistor in series with a motor will cause a drop in current draw. Unless Ohm's Law has somehow changed since I earned my Electrical Engineering degree. (It hasn't.) ;)

That is true if the motor is a resistive load. But it's not. Motors draw more current to start than to run. If enough resistance is added in series, the motor will not start. Then it can draw more current than if it was running normally at full power. Obviously, that does not intentionally happen in our case. But with age, the motor bearings might tighten up such that it will fail to start on reduced current. The result is usually a blown fuse, but it's possible for the motor to be damaged by prolonged operation in "locked rotor" mode.

True. A running motor is not a purely resistive load.
A motor draws the most current when it's not turning. That goes for universal, induction, and synchronous motors. Many high-current motors use resistors in their startup circuitry to prevent excessive current draw.
As for an automotive HVAC blower motor - if it burns up, it's relatively cheap to replace.

The real problem is if the air handler fan stops working when the A/C is on. If left running too long in that condition, it can slug the compressor. That's particularly a problem with a capillary tube.

Yes/no. The motor is cheap, but getting to it may not be. It's like replacing a light bulb in your instrument cluster: 50-cents for the bulb, four hours labor to get to it :-)

the heater does have a magic trick.

fluids in your engine go by the heads, there is an energy created, easily summed yup with "static". water is aperfect ingredient for dispersing it. the heater on can actually increase mileage.

It is like the old school trick for early large micron ECUs. Turn on the radio, tunes up the computer. The hertz in the speakers is helping disperse the clock energy in the computer. I live in very very cold climate. I learned most cars like classical high pitched violins.... The winter time really demands this tiny clock stuff.
Warm and humid, disperses this very fast. It leads to why some people call their car a pig in the spring...it is cleaning out a long stagnite keeper called winter. There is even deionization.
Heater on is good. I run mine in the middle of summer sometimes. it even helps the core, and disperses strange goops internal to the system..

AC compressor running in defrost setting
 

Wow. Quite a discussion. So how much does FE suffer if your charging system is loaded with an extra 30-80 watts? You guys are really worried about your carbon footprints:D

Running coolant through the heater core will lower the engine's operating temperature some. We used to use that fact in my younger days when we were driving POS cars that needed radiator work and we were running straight water since anti freeze cost money. Turning the heater control (assuming it worked) to high would sometimes allow the vehicle to get where we were going without overheating too much. Assuming the heater core didn't leak.

Back to the subject, a lot of cars as stated by Frank Lee do turn on the ac compressor when in the defrost mode. Some even when in the heat mode. All to dry out the air.

In the mid '80s I had an 81 Mustang in Scotland for a couple years. Petrol was about 98 pence a liter if I remember correctly. $/gal I don't remember exactly but it was a lot more than in the US. Since Scotland is a place you need your defroster a lot, I decided to try to disable the ac in defrost. The easiest thing would have been to pull the connector off the clutch at the front of the compressor. I didn't want to disable the ac as there are maybe seven days in the summer that it is hot there (to a Scot) and some of the local lasses liked to go for a drive to cool off. Some even wanted a ride out of the deal;) I pulled the HVAC control out of the dash and swapped the vacuum hose from the defrost position to the heat position. This made the blend air door put all air to the defroster vents in the heat position. No air to the floor. This created a vacuum leak at the hvac switch defrost position that I believe I dealt with by using a rubber ear plug. This did improve my dismal FE somewhat as the defroster was on most of the time I drove there.

This 81 Mustang 2.3/auto rarely got better than 20mpg and it was a total sloth as to acceleration. Never did figure out why.