A/C stopped working a few weeks ago, it would occasionally kick in for a few seconds and blow cold, but then go back to hot pretty quickly. Evacuated the system, ran the vacuum pump for 45 minutes, made sure it kept the vacuum, then recharged. Nothing, only hot air. Replaced the expansion valve and recharged, now it cools nicely when it comes on, but a couple of minutes of driving it turns warm again. If I turn it off for a few seconds and then back on, it comes out cold, but again after a short while it blows hot. Anyone have any ideas what to try next? I have a spare compressor, but that's a lot of work, especially when you live in Phoenix and you're not sure if that will fix the problem.

 

I just had similar trouble with a different brand (Opel).
The A/C had some sensor which was supposed to detect abnormal pressure conditions. This sensor was acting up.
Maybe you can read some codes with SDD ?

 

I assume you have good HVAC skills, as you were able to evacuate and refill system to spec with 134a. Below are the specs on the Pressure Cut-off switch. Based on your symptoms, sounds like someone in the past overfilled 134a to correct no cool, you temporarily fixed it by discharge/recharge. See if you can use meter to read switch output while simultaneously reading system pressure(s).

· When the compressor discharge pressure rises to approximately 2,896 kPa (420 psi), the ECM will interrupt the compressor operation and disable the compressor.
· When the pressure drops to approximately 1,724 kPa (250 psi) the ECM will enable the A/C compressor circuit.