BigWhiteGTP

For ***** and giggles has anyone ever dynoed their car with the AC on? How much power does it take to run the AC? In AZ AC needs to be on all the time but I still like to punch it to pass the lolly gaggers and cell phone talkers and people not paying attention to a green light.

By the way my car accelerates with AC on, Im thinking at least a 20% power loss at the wheels.

built91Z28

I think 20% may be a little much. I dont think its that high. Doesnt the AC compressor shut off at WOT?

Confuzed1

iTrader: (4)

Not a bad thing to test, but as much $$ as these shops charge for dyno runs, it would have to be done on their dime IMO. - unless you're REALLY interested.

Stephen

iTrader: (12)

I thought it did too.....


Our local dyno does $55 for 3 runs. So AC off & AC on wouldn't cost any extra.

Confuzed1

iTrader: (4)

That's cheaper than around here, but that's not the point. If you want to see what the car will do using one of your three 55 dollar runs, go for it.

I put mine on the dyno just to get the A/F and timing adjusted -and to see what the numbers are - but I realize they don't necessarily mean it'll get good times at the track...

I'll waste my money seeing what the car will do without the AC blastin, since I normally would turn it off anyway when I want max performance out of the car.

Again, not a bad test if you're curious....but I personally will wait for someone else to spend their dollar to find out. lol

EDIT: But if I had to take a WAG at it, I'd say 10 HP lower all the way through thr power band on a hot arizona day. - And that's HOT!!

cIaRmOaCrZo

the compressor shuts off at WOT. so it wouldnt feel any differant if you floor it with AC on or off.

BigWhiteGTP

Mine stays on. Flooring it off the line with ac on the car won't spin the tires. With it off it will. I just did like 10 runs last night. Maybe I have the worlds most inefficient ac system?

MotorMouth

When I have mine on max it keeps running.

cIaRmOaCrZo

you sure the pedal is to floor? any floor mats holding you back? and is the tps adjusted properly? when hooked up to a scanner, pedal to the floor, tps should be at 100%. BUT i believe the ac is suppose to kick off at 85% throttle anyways...

BigWhiteGTP

Everything is fine except for the fact my ac stays on at wot and sucks power. Been going over everything the last week. TPS is good. IAC is good. CTS is good. Maf is good. New o2 and plugs, new fan switch pig tail. AC was just installed at a dealership by an AC tech of 35 years a couple months ago. Ice cold. Floor mat isn't under the pedal. Just the way my car is.

Im thinking of dynoing it in the next couple months. Ill post if I do and for sure the AC will be on for the dyno.

QuickStyle

Tuner pro shows 8D speed density car that a/c is disabled at 100% throttle or 5100rpm stock. so if you are at 99% throttle it could still be on. If you can tune your own car, i'd recommend putting it at 70% and 4000rpm.

mwfrels

The number that has stuck in my head for years after reading an article about how energy inefficient automotive A/C systems are is that it takes 10 to 30 horsepower to run the average tonnage unit. The range has many variables including outside ambient, blower motor electrical load, humidity, engine speed, etc...

Mike

Reid Fleming

iTrader: (2)

Mine stays on as far as I can tell. I would think that if the A/C is on, the power requirements would be constant regardless of temp/humidity. As long as it's not cycling, what difference would it make if it's hot/humid or mild/semi dry?

Now the air temperature and dryness would make a difference to the engine even if the A/C is off. I noticed that my car felt MUCH less powerful when I first moved to Texas from Canada. But my summer time temps used to be 75°/35% humidity when I lived up north.

So I went from 180° coolant temps with one fan on or no fan on (random, sometimes it would be on when I shut the car off, sometimes it wouldn't) to having both fans on all the time, A/C on all the time, and coolant temps in the 190-210° range while driving around in city traffic) Ambients in TX summer being 95°/60% during the daytime.

Reid Fleming

iTrader: (2)

99% and still on? Who programmed that at the factory? Sheesh. I agree on the 70% and shut it off part. Although I'd go for 3500 RPM+ as the shut off point. That way it would be off after the 1-2 shift on an automatic. At 100 mph in overdrive, I'm at 3000 RPM. So it would still be on for high speed cruising. (I drove across the country a few summers back and never really cruised faster than 100 due to exhaust noise and not wanting to push the RPM's too much)

I've compared A/C on and off on fuel economy and it seems to be aprox 1 mpg difference. Not a heck of a lot. What we spend in having to air condition our cars in southern climates, we make up for in winter time in not having to deal with cold starts and long warm up times to operating temp. So in Seattle for example, although you spend close to zero in A/C costs, you spend more in the colder months, since it takes longer for your car to warm up. Roughly 1.5 to 2 mpg during late fall/early spring. Close enough that it's roughly equal on a yearly basis.

Now the 1 mpg difference depends greatly on the engine sizing. A diesel pickup truck will use maybe 0.5 mpg more fuel with the A/C on. A Prius on the other hand will go from 60 mpg down to 40 mpg with the A/C on. A gas powered 4 cylinder car will see a huge increase in fuel usage from having the A/C on as well. Our cars are higher HP for the same constant A/C load, hence the small increase in fuel economy. My wife's Blazer with it's 4.3L V6 has a very noticeable power drop while accelerating/merging with the A/C on. My GTA on the other hand is a very small difference in power.

Car A/C's are typically in the 3 ton range. 4 tons on larger cars. This is comparable to a house A/C in sizing. In Houston, the average house is 500 sq ft/1 ton. So a 1500-2000 sq ft house has the same tonnage as a typical car that's cooling an area no larger than a phone booth. This is also why cars can pump out 40° duct temps while most houses are in the 55-60° duct temps. In a northern climate, 3-4 tons might be a 2500-3000 sq ft house. City buses are typically about 10 tons of A/C. Ever notice they drip a constant stream of water out the back of the bus when the A/C is on? And they are cold to the point of being frigid despite having large windows and doors that open and close often at the many stops they make. Just having lots of people in a bus alone will increase the cooling demand. Human body temp is aprox 98° per person.

People in Alaska get terrible fuel economy starting up their cars at -40°. In fact, you actually save money by leaving your car idling at the grocery store and visiting friends there, because the fuel economy at warmed up temps is so much better than the cold starts at -40° with the car having been shut off, that less fuel gets used and it's better for the environment......As you can imagine, a catalytic converter does absolutely nothing at -40. The fuel ratio runs pig rich. Injectors are getting raw liquid fuel rather than vapour fuel in order to start the car and keep it running. AIR injection helps a bit, but the air temps are still too cold to burn cleanly/efficiently.

I told co-workers here in Texas that my (Canadian) car has a block heater. And none of them knew what it was.

mwfrels

That's some good data on a/c sizing. I learned some from it.

As far as mileage loss and power loss on cars I agree it depends a lot on the vehicle. Our SBC F-bodies only see about a one to two mpg drop with a/c on and very little in power loss. Some cars like my wife's '90 Camry sees a two to three mpg drop with a/c on and a SIGNIFICANT loss of available power from its little 2000cc four cylinder engine.

I reference to winter driving down here in the South we are privileged to be able to keep our cars on the road 365 days of the year with very little winter discomfort. Unfortunately politicians of the past seemed to think we do have really cold winters here and forced reformulated gas upon us in Harris and surrounding counties to hold down emissions during cold starts and running. My car sees a two mpg decrease when RFG is put to use for the winter season. My best mileage is a two to three month window in the spring and fall between A/C and RFG use.

Anyway...enough rambling on a Sunday afternoon.

Mike

camarosrock1989

iTrader: (1)

I only have a 2.8 v6 in my 89RS, today it was 94 deg, I turned on my AC and loss alot of power,after draging my *** i turned it off. And gained the power back. Looks like I won't be driving my car that car this summer.

mwfrels

Unfortunately for you that "10 to 30 horsepower" drain I quoted is a more significant number than mpg. On my wife's poor little Camry the a/c seems to steal 1/2 the engine output. It is difficult sometimes to justify turning a/c on so I understand your plight.

Mike

mav75

Is that 10 - 30 hp number accurate? It sure feels like a lot more than that to me. I'm in Houston too, and I have a 305 TPI. Running my car at max AC turns acceleration into something more theoretical than practical. In plain english, the car's a dog with the AC on, but for the few times I would actually take it on the road in the heat down here, I'll just take comfort over power and stay in the right lane.

mwfrels

I understand the feeling. When my car was LB9 the a/c on made a big difference to the butt dyno. With the 350 now in the car the a/c has much less impact.

M

Gambit69

Now here is a thought that I have had. I might be crazy and it may never work but it would be interesting to see someone do try it to see what the outcome is.

Since colder air makes more power, what if the air from the ac was going into the intake? Would it be enough to offset the power that is needed to run the ac and give you a little extra boost or would it be a big flop and not gain you anything. The piping would be insulated so the heat from the engine wouldnt take away from the colder air and still have the main pipe with the filter on it still pulling into the intake as well. have some kind of shut off blocking off the ac pipe so it would only open when the air was turned on. I know it wouldn't be supercharger or turbo numbers.

Its just a thought and like I said i could be crazy about this but I did see in either Car Craft, Hot Rod magazine or another one like it, they hooked up 2 leaf blowers to I think it was a 90's corvette and it was similar to a supercharger. So anything is possible on the outcome of it.

mav75

I still say every penny I spent to convert and recharge the A/C to R134 was well worth it. But then again, If it's going to be that hot out, chances are the car will be in the garage anyway, since I like driving without the t-tops, but not if I'm going to sweat my *** off. Besides, I don't want the (original) paint, dash, or for that matter, 90% of my interior baking and cracking in the brutal blast furnace that Houston jokingly calls the sun.

Reid Fleming

iTrader: (2)

What kind of duct temps do you get with R-134a in Houston?

MotorMouth

I tried to find the article I read several years ago Ford did that to a concept car. It did add to the HP numbers and to the fuel mileage at top speed. It seems that's as far as it got was just a concept car.