takkar

It's a common thing with most old cars that when the A/C is turned on ( or when the compressor is turned on), the car feels much slower ( atleast slower than when i bought it) . Is there anything that can be done to fix this?

NYPD-Arnold

iTrader: (8)

I don't know about much slower, but throttle response is definitely lost. I usually throw the CC to Auto, let all four vents cool up to 60 and then bring it down to only one vent. You don't need the AC to be on full blast all the time.

takkar

i dont think the speed of the fan makes a difference...the compressor will work at the same level at all times. it only turns off whenever the desired temp inside is reached...

irish44j

iTrader: (38)

um, with the A/C on, additional power is being diverted from the wheels to run the compressor....

Larrio

iTrader: (10)

its a common thing on all cars.

the AC pulley is magnetized so it spins freely until you activate it and the pulley tightens up producing more drag or resistance against those drive belts, slightly slowing down the vehicle performance and response.

deezo

iTrader: (3)

Just don't plan on racing the car with the AC on. When it's hot enoough out to drive with the AC on, I take it easy on the car and don't try to over work it.

NYPD-Arnold

iTrader: (8)

Very weird. My car feels totally fine when only one fan is on. When all four are on it feels slower.

Metal Maxima

iTrader: (30)

Damn, I did not know that. Good post.

MacAlert

iTrader: (1)

Theres only ONE fan. Closing the vent does only that, closes the vents. The fan will still be blowing to all vents regardless if it is closed or not. (closing the vent is mechanical, not electrical)

NYPD-Arnold

iTrader: (8)

I don't think that's correct. The difference in air intensity between having all four fans turned on and just one is immense. I'm not talking about closing the plastic vents on the dash, I'm talking about the climate control itself. When the CC is set to four fans the car feels like a dog. When it's set to 1 fan it feels fine. When it's set to 4, it's loud and you can hear the air blowing in. When it's set to 1 it's quiet and no where near as intense, and still blowing through all 4 vents.

Edit: BTW, I know there is only fan. I'm just talking about the LED display that shows the intensity of the AC. The more fans, the more intense. The more intensity, the more strain put on the pulley.

MacAlert

iTrader: (1)

Ohh, thats fan speed. Not how many fans are on.

2K3MAX2NV

iTrader: (10)

yea but dont you love it when the stealership says "the a/c doesnt blow cold enough"

Lytheum

yeah...with ac on my car has no throttle response. its lag lag lag lag.....then POWER. maybe that just my vtec kicking in

Epacy

iTrader: (6)

DAMN IT!!
...

BlackBIRDVQ

iTrader: (15)

I can barely feel my AC on, but then again I have a underdrive Pulley from Unorthodox and Fidanza flywheel :P

ILLJIM69

mines the same........but i never ran it anything below 2 "fan blades". im gonna try all the "fan blades" all the way and then just one.....but its fricken hot in arizona, i love A/C!

jim

bladerunr

iTrader: (14)

Invest in an under drive pulley (UDP).

Maximax2

Yep. Interestingly though, I've found much less of an effect since the timing advance. There's still a power loss with the AC on (and believe me, living in Houston in the summer - it's on...), but the engine still feels strong. Added torque helping out? Dunno.

Also, on most cars, including ours I believe, the compressor will shut down at WOT allowing max power. You'll notice the effect if you floor it and run up to 80+ - the air coming out of the vents starts warming up.

igzy

iTrader: (18)

The way AC works is that the climate control senses the internal temperature and compares it to the set temp and then if on AUTO control, it decides if it should turn AC on or not and blower fan speed (fan blades mentioned above). When AC comes on, compressor engages (up to this point only a pulley ring is spinning freely - with least resistance to the drive belt). When compressor turns on, main shaft locks the pulley (clutch engage) and the drive belt turns AC compressor shaft and builds pressure inside the compressor (air compression = buildnig presure -> in chem. PV=nRT) which cools the freon and that cools the air in the vent passages. When compressor engages, idle is raised by computer by about 100-200 RPM to compensate for the drive belt driving the extra load of the compressor on the belt and as such you will feel the "loss of power". So yes, some power is diverted to the compressor and not sure but I think it is something like 3-5 HP are drawn from the engine as the result. Number of fan blades dictates how cool you want your interior to be - the more "blades" you have the longer the compressor will stay engaged to try to cool the car, if you have only a few blades going it only turn the compressor on occasionaly... So to answer your original question: there is nothing you can do to eliminate the loss of power when AC runs except that you can minimize it by making sure your compressor is operating properly, don't set the cool temp to the lowest setting, run it at a few deg above minimum or not run the AC at all (don't use AUTO but only ECON setting that will not turn the comrpessor on). I cannot speak to UDP as I have no experience with it :-)

Bones45

power is not "being diverted from the wheels to run the compressor"

igzy

iTrader: (18)

Well, I think it is more like: more power is required by the main pulley to drive the compressor and that power comes from drive belt going over the main pulley (UDP), i.e. harmonic balancer attached to the crank and it is drawing power from the engine so you will have less power at the wheels...

mert

Does the a/c suck in this model of maxima?

I'm used to a 2000 camry, and just got a 2000 maxima. During a recent 100 degree weekend: In the camry, I'd run the a/c with the fan on 1 or 2 and set all the way cold. In the maxima, I had to run it with the fan on 4, and I still didn't get that cool. I took it to a tune-up shop and they said it was a little low on freon, they recharged it but it didn't make much of a difference.

I spotted a guy at the dealership that had the same model, and he said he has to run his with the fan on 4 all the time too.

Bones45

My hondas a/c was always decent at best...nissans seem similiar.

NYPD-Arnold

iTrader: (8)

Ahh, that's why 2001 Maximas rock. We go down to 60 and up to 90. My A/C blows just great.

takkar

Nissan A/C are known for not being the best. I think Toyotas and Hondas A/C cool much more quickly than Nissan ( atleast the Maxima's)

spirilis

iTrader: (2)

In a manner of speaking, it is. Power isn't being diverted from the *wheels*, it's being diverted from the engine, which means it never reaches the wheels (so it never reaches the transmission, never reaches the differential, never reaches the axles, and therefore never reaches the wheels).

The A/C compressor, when its magnetic clutch engages, adds extra mechanical load to the drivebelts at the front of the engine, therefore making the crank pulley more difficult to turn. As a result, the engine's pistons are now pushing against greater load than before (load = load against the transmission, internal friction/compression, and now in addition, the extra load from the A/C)--since they can only output a certain amount of torque at any one time, this extra load ensures that the engine cannot spin up the crankshaft as fast as before, whereas turning off the A/C (or having the compressor clutch click off) restores original operation. This is perceivable as the A/C compressor "stealing" power from the wheels, since the effect results in less acceleration.

I'd imagine this effect is proportional to the amount of torque required by the A/C compressor in comparison to the size/torque output of the engine--i.e. a more powerful engine shouldn't see nearly as much trouble with a 15HP compressor as a 4cyl 115HP econobox would :P

mert

re a/c efficacy:

that sucks. guess it's time for a dark tint.

MaxArt

spirilis, good reply. Now let the professor make it more complicated. Many modern cars not only have an electric A/C clutch that can be programmed to disengage at WOT (you can actually feel it cut in and out), they also have variable vain compressors rather than the old piston type. This means the output (and load) can vary depending on demand and driving circumstances. Therefore, with high fan speed (the little blades), high temperature differential and light or medium throttle you'll probably feel more power loss than on cool day with less demand on the compressor. Pretty much everything driven off of the engine can be thought about similarly. Take the alternator (laws of physics - you don't get something for nothing and nothing sis 100% efficient - thus heat and power loss). With all accessories etc. off their is a small load on the alternator and the pulley is relatively easy to turn. Turn everything on (rear window defroster, lights, radio, accessory outlets etc., etc. and you require more work to generate more output and the alternator becomes very hard to turn. Do it all on a hot, steamy evening and you've dropped a big chunk of turning power which is no longer available to the wheels. Or you could put 300 lbs. in the trunk and drive with the emergency brake on to achieve the same effect. Thus as stated above, the less power you start with, the higher the percentage of loss and the more noticeable. Enjoy thinking about it. Nothing is free, even though manufacturers have turned to electric driven water pumps, steering pumps etc, there is still some loss with increased load.

Maximax2

Just wrote a note about this in another thread. At temps above 85 or so, make sure you're running recirc; that way the A/C is cooling down air that's already relatively cool. This helps a lot - otherwise, with fresh hot air coming in, the car is always trying to catch up.

It still takes a while for the car to cool down, especially if it's been outside. Now that I think about it, here's my advice to cool down a car that's been sitting in the sun in hot temps.

1. Auto roll down windows as you walk up to it, to let the hot air escape.
2. Start the car, run A/C for a minute or so with windows still open and recirc off - the air in the car is still likely hotter than the outside air.
3. As you start rolling, roll the windows up and switch to recirc. By this time the air in the car is cooling down, and max cool is achieved with recirc and internal air only.

Works in Houston, it was 97 here a few days ago.

Peace