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electric fan vs mechanical one

70monte on Wed March 25, 2009 4:59 PM User is offline

Year: 2008
Make: Chevrolet
Model: Trailblazer SS
Engine Size: 6.0L
Refrigerant Type: R134a
Country of Origin: United States

Working on my friends 2008 Trailblazer SS had me wondering about this question. My friend had a supercharger installed on his Trailblazer SS with the 6.0L. One of the modifications done was to remove the mechanical fan setup and install an electric one. Its a single fan setup which he says pulls more air than the factory mechanical setup.

Does this type of modification change the dynamics of how the AC system works compared to how it was stock? I was wondering if the AC system would be as efficient with the electric fan setup as it was with the mechanical fan setup. Does it even make a difference. Thanks for any info.

Wayne

Edited: Wed March 25, 2009 at 5:00 PM by 70monte

TRB on Wed March 25, 2009 5:19 PM User is offlineView users profile

Only thing that really matters is the amount of air flow directly across the condenser. How the best results are achieved is irrelevant be it fan type or doing 100MPH.

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When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com

bohica2xo on Wed March 25, 2009 7:45 PM User is offline

Generally when I hear about an electric fan that "moves more air than stock" - I know that there is some smoke, a mirror & some bs involved.

It is possible for an electric fan to move more air than the OEM mechanical fan at idle - if the mechanical fan is running on a warm clutch. The aftermarket fan companies all play this game, measuring airflow on a stock fan at minimum output, vs the electric fan @ 14.9 volts.

Once the engine goes above idle, all bets are off. That mechanical fan can absorb many more horsepower than the alternator does - and it moves more air as a result. On many vehicles, an electric fan is just fine. A vehicle like a Mk VIII Lincoln spends little time above 1200 rpm with no foreward speed to aid cooling. There is a brief spike in the high side as compressor rpm comes up before road speed improves condensor airflow.

If you are towing with that Trailblazer, it is very possible to run the engine above 1500 rpm with little or no road speed for much longer than the Lincoln. The radiator & cooling system can absorb the added heat for a little while, and it may not even show up on the OEM temp gauge. The high side on the A/C will definitely show it, and you may see reduced cooling in this mode.

GM put that huge fan on there for a reason. If an electric unit was any better, it would have been there. Automakers are constantly chasing the CAFE dog, looking for every last drop of fuel economy. Removing the 20hp fan drive would be high on the list, if they thought they could get away with it.

Put your gauges on it, and go for a drive. Remember the direct correlation between high side pressure & temperature...

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

70monte on Wed March 25, 2009 8:29 PM User is offline

Thanks for the replies. This is not my vehicle so I'm not sure if he tows anything or not. He is definetly after more horsepower. The AC has not worked for quite a few months and this is the first time since the upgrades that the AC has worked so I don't know if he even remembers how cool it used to get. I will mention to him that the AC might not cool at higher speeds due to the electric fan. I'm not exactly sure why the stock fan setup was removed because it doesn't look like the supercharger would have been in the way.

Wayne

TRB on Wed March 25, 2009 8:48 PM User is offlineView users profile

Most likely it was removed for HP.

-------------------------

When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com

iceman2555 on Wed March 25, 2009 9:27 PM User is offlineView users profile

Many of these 'high flow' electric fans fail to mention the amperage necessary to achieve this tremendous air movements. One of the major producers of 'high performance' electric fans..those that move more than 2500-2800 cfm state that the amp draw on many of these units may exceed 35-40 amps. Many of todays charging systems simply do not have sufficient 'free' amps to achieve this. It is hard to beat a properly functioning OE engine driven fan system. Esp one with the correct and fully functioning fan clutch...electrical activated or thermal.
Go along with TRB....it was the HP thing.

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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

NickD on Thu March 26, 2009 6:29 AM User is offline

My HVAC outdoor unit uses a wide five bladed fan 20" in diameter running at 3450 rpm with a 1/3 HP motor. Would have to look up the cfm displacement, really has quite a blast, but certainly doesn't draw 20 HP. A fan like this would consume around 30 amperes from the alternator and with inefficiencies of the alternator and drive circuit would put a one HP load on the engine as opposed to a 1/3 HP if operated directly, so nothing is gained by going electric, but quite a bit is lost.

Worse yet, the alternator has to produce the maximum amount of current, when it's least capable of, at idle speeds. As the vehicle speed increases, the load on the fan is greatly decreased, the windmilling effect, even to the point, say at 100 mph, some of that wind energy is being used to help propel the vehicle, but certainly not a gain as other wind resistive forces, like the front of the vehicle increase by the cube of the speed. But that is the problem, not the fan. With all the other inefficiencies associated with even the modern automobile, the fan is the least likely culprit in the lost department, yet it gets all the attention. Crazy, isn't it? But that's marketing, zero intelligence, 100% BS.

bohica2xo on Thu March 26, 2009 4:10 PM User is offline

70monte:

I did not realize you had posted pressures in another thread. Your results at 60f are your answer. a P/T ratio of 2.5 at that low ambient heat load is staggering. It will not get better @ 100f . If you took those readings at idle, you will be even worse at 1500 engine rpm. Your numbers would be bad for a converted system - and this is a near new OEM system designed for 134a!

Get the mechanical fan back in place if you want A/C.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

70monte on Thu March 26, 2009 8:00 PM User is offline

bohica,
Since this is not my vehicle, putting the mechanical fan back on is not an option. My pressures were at idle. I talked to the owner today and told him what has been said so far about this topic. He didn't seemed too concerned about it. I guess we will see how he feels when the outside temps get up there and his air doesn't work as well. He is happy with it at the moment.

chris142 on Thu March 26, 2009 11:37 PM User is offline

FWIW mechanical fans are rated @ 2200 rpm. The average mechanical fan with a properly working fan clutch will move close to 10,000 cfm @ 2200 rpm.

As him how much air the electric fan moves.

TRB on Thu March 26, 2009 11:48 PM User is offlineView users profile

Quote
Originally posted by: chris142
FWIW mechanical fans are rated @ 2200 rpm. The average mechanical fan with a properly working fan clutch will move close to 10,000 cfm @ 2200 rpm.



As him how much air the electric fan moves.

Chris most of the higher end electric fans depending on size will move about 2100CFM at maximum amp draw. Of course static pressure will very the results.



-------------------------
When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com

bohica2xo on Fri March 27, 2009 3:22 AM User is offline

70monte:

Just stand back, laugh & enjoy the show then. Expect it to cycle on the HPCO on hot days, make odd compressor noises, etc. Be a race to see if the compressor or the transmission craps out first. Some great watching if you don't wrench on it.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

70monte on Fri March 27, 2009 6:06 PM User is offline

Well, the transmission won because its already slipping pretty bad. He is in the process of finding someone to rebuild it stronger. It only has a little over 19,000 miles on it.

The electric fan looks like a pretty big one. I will have to ask him what its flow rate is. He hasn't spared any expense on this thing. He also had headers and a catback exhaust system installed at the same time as the supercharger.

I hope the compressor doesn't crap out because I don't want him to blame me for doing something wrong. I put the correct amount of refrigerant in it. Is there anything else that can be done to get the AC working properly with the electric fan? Are the AC systems on vehicles with factory electric fans set up differently than ones with mechanical fans? Are you guys saying that the AC pressures will be too high at higher ambiant temps running the electric fan? I don't know if I could convince him to put the mechanical fan back on. Thanks for all the info.

Wayne

TRB on Fri March 27, 2009 6:32 PM User is offlineView users profile

Here is some data from a popular fan supplier.

Specifications Part #
292,295/298 puller

Mounting Surface Required
17½" x 27½" x 4"

Fan Diameter
Dual 13½"

Fan RPM @13.5VDC
Variable 1260-2100

Number of Blades/Fan Blade Angle
8/26°

Airflow-Cu. Ft./Min. at 0º Static Pressure
2760-4600

Amp Draw
16-28



-------------------------

When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com

Matt L on Fri March 27, 2009 10:18 PM User is offline

Does that vehicle have a way for the AC system to turn on the fan for high side pressure and/or temperature?

NickD on Sat March 28, 2009 6:53 AM User is offline

In engineering in we have a term called RSF, reserve safety factor. For example is you wanted to lift a hundred pound load and used a rope with a rated strength of 100 pounds, the RSF would be unity. But more typical in automotive design, a RSF of O.9 is used because likely that load of 100 pounds will never be reached, statics show the average load load with speed limits and all that would be more like 20-25 pounds. Have to do that to keep profits up and keep the stock holders happy.

Headers nor that catback super duper exhaust system won't hurt much, except foul up the OBD II system as for proper emission controls, a restriction is required, you never mentioned if is CEL is also acting up, but have a feeling it is.

But just bolting on a supercharger on a stock engine sure won't last long, unless it also installed rated pistons, connecting rods, and a crankshaft, supercharging requires using lower compression pistons so you don't blow either the head gaskets or the heads themselves. and those stock rods can't handle it either. His AT problems is just the start of it.

Son's friend did that, gave him the same advice, but decided to listen to his shop at St. Paul with rather impressive dyno readings, he hit the gas pedal once, and that was the end of it, blew his engine. Stuff like this has to be done from the ground up alone with brakes, drivetrain, and suspension. BTW, these super fast dragsters are only good for 2-3 six second runs, and have to be completely rebuilt, that gives a life of about 18 seconds maximum. Have fun.

EVtech on Sat March 28, 2009 10:36 AM User is offlineView users profile

After working on ambulances for several years in a warm climate, I agree with whats been said about fans. A good mechanical fan is by far a lot better than an elec. fan, but like one fellow said, when your moving down the road at highway speed, both of them are probably just parasites. I would also like to point out that elec. fans have a much higher failure rate than mechanical fans. Sometimes they just quit working and sometimes they will slow down in r.p.m before they totally fail.

bohica2xo on Sat March 28, 2009 10:26 PM User is offline

Wow, they just keep making that transmission lighter & lighter.... Not so good for high horsepower though.

I talked to a friend today, that runs a Whipple blower on a 5.7 GM. I asked if the reason they pull the fan is to make a mild blower seem more powerful - it took him several minutes to stop laughing.

The real reason they dump the fan? Belt horsepower. They do not add a crankshaft pulley to drive the blower. The poor little six groove serpentine was (as Nick pointed out) maxed out with the fan & accessories. My friend still runs a stock fan, and it eats belts. 7500 miles is a good time to change them - if they make it that far. Everyone tells him to dump the fan & go electric. He knows better.

When the OEM adds a blower to that GM 6.0, they add a crankshaft pulley just to drive the blower. Look at the factory supercharged caddy.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

NickD on Sun March 29, 2009 8:25 AM User is offline

Even though my sons' friend which would of made me a friend like the OP, I wouldn't touch his car with a ten foot pole, I knew it was going to blow, and if I did anything to it, whether my fault or not, it would be my fault, not good for family relations. When he had problems, could only suggest he take it back to his shop in St. Paul that made all the promises and have them honor any warranties.

If the OP gets involved with this, and if anything goes wrong, could very well be the end of that friendship, even a liability charge. We live in a strange world today. I have helped my kids other friends with other car problems when trying to go to college with no money in their pockets, but was all stock with obvious problems to be repaired.

70monte on Mon March 30, 2009 7:56 PM User is offline

I told my friend the newest info from here regarding his AC and he still is not worried about it. He says if the AC compressor starts making noise, he will just not use it. I told him I would check the pressures again when it gets warmer. He told me he won't be mad if the AC system blows because he knows the vehicle has been modified.

As far as his modifications, go, the only engine modification that I know of is a different camshaft that gives the truck a loping idle. He does also have a K&N air filter tube instead of the stock setup. His CEL is not on. He does plan on replacing the stock pullies with different ones. He also has to do something else to the supercharger system because the supercharger boost is not where its supposed to be.

He freely admits that he has voided his powertrain warrenty by having all of these modifications done. I wouldn't have done it but it was what he wanted to do. It does feel pretty powerful though. I guess we will see how long it holds together.

Wayne

Edited: Mon March 30, 2009 at 7:58 PM by 70monte

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