Questionmy kia spectra 2002 a/c runs cold then warms up then cold again. I added some r-134, but does not change.The compressor I think is working fine.
AnswerYou have two pressure safety switches inside your system. One for the high pressure and one for the low pressure. The low pressure cuts off the compressor when the pressure drops below a certain point, typically between 16 and 26 psig) At idle your compressor is not turning as fast therefore your low side pressure switch stays engaged. The faster the engine revs, the faster the compressor turns therefore it is going to pull a lower pressure on your low side, and may be disengaging your switch. With the compressor off, the pressure begins to ezualize, and your low side begins to rise, when this happens, your switch closes, and it all starts over again. This is called cycling. It is very possible that your refrigerant charge may be low due to a small leak. As the engine develops higher rpms, it pulls the low side pressure below the opening point and shuts down your compressor. With your pressure readings I can expand more, but from the sound of it this is the most likey cause. A low refrigerant charge.
The other switch is your high pressure switch. It shuts down your compressor when your high side pressures reach too high of a level. The usual cause for high pressure is a dirty condensor. The condensor is located in front of your radiator. Check it and see if it is covered in leaves, dirt, or other road grime. If so, a good cleaning with a regular water hose will do wonders. Also check to see if more than 20% of the aluminum fins on the condensor are damaged, or bent over to the point that they would block air flow through the condensor. No air flow = high pressures. On the same note, make certain that the condensor fan comes on and off. Your vehicle may use the same fan as the radiator, or it may have another on the front of the condensor, I'm nAot certain of the specifics of your car. But if it is not pulling air through the condensor, that will create high pressure and can open your high pressure switch, shutting down your compressor.
The A/C world is controlled by pressures and you would be amazed at the different things they can tell a technician. If you can send me the readings from your high side and low side, with the A/C on and the engine about 1500 RPMs, as well as the ambient temperature when the pressure was checked, I can probably get to be more specific.
Thanks for your question and I await your follow-up with pressures.
