QuestionQUESTION: hi,
i have 1998 model maruti zen lx,, when i switch on my A.C. my car represents lot of load on its engine.. there is no fine response on a.c. even if i press the acc. paddle fully. but when i switch off the a.c. its like vroom. kindly make me clear that what may be the causes of this problem..
regards
ashit kaushik
ANSWER: First, I am wondering if the car has always done this, or has just started to do it and that is what has you worried. If it has just started, then I would be suspicious that the A/C compressor is on the verge of failing. An A/C compressor absorbs a lot of horsepower. In the old days GM used a compressor made of cast iron that would cool a small office building; it could absorb 25 or 30 horsepower. Even the lightweight high-efficiency rotary compressors used today will absorb 10 or perhaps a little more horsepower. If the compressor is beginning to fail, the power absorption could go up to as much as 15 or even 20 right before failure. If that's the case with your car, you will know soon enough. If we are talking about the ordinary absorption of horsepower in everyday driving, then you are, of course, correct; it's vroom without it and piddle-paddle with it on. If you want to do something fairly simple to remedy this, they make (I really have no idea where you could get one in India, but I'll bet that you can if you hunt around) a small vacuum-operated switch that can be plumbed into your car's vacuum system. It should be hooked directly into the main manifold vacuum, not the ported vacuum used for distributor advance or other purposes. It is wired in series with the connection to the electromagnetic clutch on the A/C compressor. When you floor the accelerator, the switch, in response to the drop in vacuum signal, will open and cut off the compressor. Then, when you let off the pedal, it turns the A/C back on. Once it's hooked up and operating properly, it becomes completely invisible to the driver. And, it will save fuel (although not much) as well. An alternative to this type of switch would be to mount a micro switch on the throttle assembly and use a relay to cut off the compressor when the throttle is moved past a certain point. Many modern vehicles already have a switch like this which is used to trigger the WOT mode in the fuel injection; you could piggy-back your A/C cut-out off of the same switch. Air conditioning in small-engined cars really does affect performance, and you probably want to just turn it off during spirited driving, but a cut-out like I have described will let you drive normally and still be able to accelerate hard to get around a truck on the highway.
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QUESTION: it is really a gud solution of the problem Mike. thanks for the suggestion
but i really wants to know that generally in a hatchback car like mine that is of 1000 CC, What would be the decrement in the percentage in acceleration power of my car.
i make you sure that my car already complete around 150000 kms.
thanks
Answer A 1000cc car is pretty small by American standards, but probably a sensible size since our cars tend to be much bigger than they need to be. A car like that probably makes about 50 peak horsepower. An A/C compressor probably absorbs about ten horsepower. So, you can see that you are going to lose about 20% of your power with the A/C compressor on. But it gets worse. The A/C compressor absorbs the same amount of power all of the time that it is on. So, if you are going down the road with the A/C off at, say, 70kph, you are only using about 9 or 10 horsepower (with such a small car, maybe even less) to keep you going. At a steady speed you are just overcoming aerodynamic drag (low at that speed) and the rolling resistance of the tires. Now, if your engine is only putting out 9 horsepower and you turn on the A/C, which absorbs 10 horsepower, without opening the throttle further, you are actually going to come to a stop. Of course, you won't because you will depress the throttle further, causing the engine to make enough horsepower to run the A/C and keep the car going, too. In some circumstances, like on a hill, you will probably have to shift down to a lower gear in order to continue making progress. And if you have to double the output of your engine, what happens to your fuel economy? It is cut in half, that's what. So, while A/C is a very welcome luxury in hot weather, you will pay for it in increased fuel use. And, the smaller the engine, the larger a percentage of power loss or economy loss you will have.
I had a car back in the '80's, a Lincoln MkIV, with a 7.4 liter engine. It had one of those old GM compressors (I know it sounds odd that Ford would use a GM compressor, but it was the only one big enough) that are capable of cooling an office building by themselves. However, because of the inexcusably large engine, I really never noticed whether the A/C was on or not. And, this car probably weighed over 5000 pounds. We Americans have a lot to answer for, but it seemed like a good idea at the time.
