Problem with AC + CNG

Hello All,

I am a new member, in the sense that I have been reading posts for past several months but have posted rarely.

I have a model 2002 Spectra.

The problem is that when running on CNG, the engine stalls if AC is turned on when engine is idle. No problem happens when accelarator is pressed (i.e. during normal running). When engine is put into idle state with AC on, the RPM sharply dips. Petrol being more powerful feul overcomes the dip, but CNG fails.

My second observation is that the situation becomes a bit better after a long run, e.g. more than 30km. RPM still dips, but even on CNG, the engine is somehow able to overcome the dip in RPM. After a day or two the problem re-appears.

I am a novice as far as engine technology is concerned, whatever I know is due to Pakwheels and experts contributing to it. For which, MY BIG THANKS to all.

My guess, so far, is that source of this problem is either of the following 2 reasons:

1. Wrong Idle RPM setting for CNG.
2. a) Weak battery b) Weak alternator

(My guess may be totally wrong)

I had got the car tuned and changed battery just a couple of weeks ago.

If my guess#1 is correct, then I will appreciate if any one can guide me on how to set idle RPM setting in Spectra. This problem was not happening at the workshop, and started happening after a week or so. I will also appreciate if someone could tell me why the setting changed in such a small amout of time. (BTW, I get gas from only two stations. One near my office, one near my home)

Again Thanks in advance.