Hey any help would save me time. seached all the post coudnt find any. 1993 PONTIAC SUNBIRD 77k miles. engine surging only with ac on. ac doesnt cool when idling either. Thanks for the help in advance

 

Is the compressor cycling in time with the surging?

Cooling fans running like they should at idle?

 

cannot tell about the compressor cycling but the cooling fans do not seam right

 

Does your car have a voltmeter as one of the instrument panel gauges? If so, what do the volts show when idling?

If you don't have such a gauge, or it doesn't seem to work, (and perhaps even if it does) use a voltmeter to test volts at battery terminals with the a/c off, and then again with it on.

I wouldn't doubt whether you have a low volts condition with low alternator output at idle and this is causing weak ignition and weakness for the car to even make the electrical engage the clutch for the a/c and/or the blower speed may even be slower..

Just a guess, but that is where I would start my search. Then post back after making some of these confirmations.

 

Since you are fairly certain that the car is surging only when the A/C is on, and given that the A/C system is not cooling-it would make sense that the car is low on freon. When the compressor kicks on-the car will momentarily shutter due to the added load on the engine. Now in your case the compressor is kicking on, and then immediately shutting off due to the low pressure switch (low on freon) cutting the compressor off. After a moment, the compressor will try to engage again, then the low pressure switch will turn it off again, repeat the cycle, repeat the cycle, and you have your surging.

Check freon level first. If that checks ok, then check for a faulty/failing low pressure switch and replace. My guess would be low on freon. If that is the case, when you re-charge it, get dye put into the system because you DO have a leak somewhere. Good luck.

 

Thanks Go69 yeah I just bought the car and the mechanic installed a used pressure switch. lol I never worked on a/c before switch easy to replace?

 

Easy, but you have to remove the refrigerant and then recharge after doing the switch which means it's not a DIY job.