Automotive Air Conditioning Information Forum

First off, I've tried to read and search to see if this problem is common and I'm not able to find anything already discussed. If I overlooked something, I apologize in advance. Also, thank you for any help anyone can provide..

I have a 2007 pt cruiser, non turbo with 39k miles.

I turn on my car, set air condition to max. open the hood and connect gauge to low pressure side of a/c. At idle with the ac compressor running the gauge is reading apx 42 (in the green). The vents blow cool but not cold air, mostly feels cool just because of the volume of air movement.

There is then a change where the compressor begins to cycle on and off with the pressure climbing into the red then the compressor comes back on and the pressure returns to apx 42. This happens about 5 to 10 times with a steady on/off interval of about 5 seconds. Again, there is no cold air, no change in air temperature.

Then it seems as though the engine is straining a bit and the pressure will drop to around 5-10 and the compressor cuts off and the pressure grows back to 42 and the compressor kicks in and the pressure drops and this repeats about 5 to 10 times but I can feel a fluctuation in the air temperature of the air coming from the vents.

The pressure will then return steady to about 42 and the air goes back to where it was in the first paragraph. This whole cycle will repeat.

Originally, the compressor was not coming on, so I replaced the a/c switch (low pressure sensor) near the firewall on the passenger side. Once I made that change, which I tested first by jumping out the wires attached to the sensor which allowed the compressor to engage, I then replaced the part.

I do not know what to do

The low-pressure-only gauges that come with the refrigerant cans are notoriously inaccurate and unreliable. These cans, known as "death kits" in the trade, often contain refrigerant and sealer. You definitely DO NOT want any sealer in your A/C system. Trust me on that.

To get a better handle on what's happening with your A/C, at the very least you'll need an accurate manifold gauge set that measures both low pressures and high pressures. This site's sponsor offers an excellent professional-grade gauge set.

Although your car has only 39K miles, it's still 11 years old and probably has a slow refrigerant leak someplace. Mobile A/C professionals report that the majority of cooling problems result from leaks, which can be very challenging to find.

Mobile A/C isn't DIY friendly, can be hazardous to work on, and can result in additional expensive problems if you lack the proper equipment, training, and experience to work on it yourself.

If you don't have the know-how and equipment to troubleshoot this beyond just measuring temperatures and pressures, I advise turning the job over to a professional, who will most likely save you time and money in the long run.