Engine Pulses when AC turned on.

[DJD-Rod]

Hey guys, I have a mk4 2003 Jetta 1.8T Awp engine. I noticed that whenever I turn on my ac, i can feel pulses on the steering wheel. I notice that my vacume (on the boost gauge) goes from about 20 hgz (or what not) down to about 16hgz. I only notice it at idle with the ac on.

Now i know my alternator is on its way out (lights dim and what not) And one time, I was blasting bass in traffic and my car stalled (battery light went on). swapped rthe batter with a big a** one (for free!) which i havent had that issue anymore (with the stalling). Yet, im wondering if because of the extra load on the alternator because of the A/C, could it cause these vibrations?

As far as the rpm goes, it dosent really move with the pulses. The rpm pointer seems pretty stable, although it does fluctuate a little, weather the Ac is on or not. But bearly anything.


IF any of you pros could chime in and lend a hand or tip, id be very thankfull!!

thanks guys

[BoostedGLS0218]

Your driving a 4 cyl car. They all struggle a little with the ac. The fact that your having alternator probably doesn't help tho.

[Rivals Inc]

Your driving a 4 cyl car. They all struggle a little with the ac. The fact that your having alternator probably doesn't help tho.

especially at idle. Yes it's normal. Mine does it to. Get your alternator fixed soon though.

[DJD-Rod]

especially at idle. Yes it's normal. Mine does it to. Get your alternator fixed soon though.

But is it normal to pulse when it's on?

[Rivals Inc]

Yeah. Worse case scenario, you are out of refrigerant thus causing your compressor to cycle (to kick on) 15 times a minute. and if you were out on refrigerant then you would have noticed your car not cooling.

[DJD-Rod]

Yeah. Worse case scenario, you are out of refrigerant thus causing your compressor to cycle (to kick on) 15 times a minute. and if you were out on refrigerant then you would have noticed your car not cooling.

Hmm, the ac is pretty cool , even on hot days. I do notice I need to really ride that clutch cuz it takes such a load on the engine. I'm convinced it's my alternator. Although , sure isn't a cheap repair .


The pulsing is similar to "vvRRvvRRvvRRvvRR" haha :p

Although, it has pulsed in other ocassions! Once after usig my subs, and anoter just after a casual drive to work, nothing fancy, no ac.

Ugh, cars and their annoying problems: /

[K20017]

To give you an idea how much the AC affects a 4 cylinder, usually my car has a nice lope at idle from the cams. When I turn my AC on, it actually smooths my idle out as drops my vacuum to 5inHg from 10in.

And if I want to get out of first with the AC on.... Forget it.