Low side high, high side low?

[PeterW76]

Hi. New to this forum and seeking some help to diagnose a problem. I just bought a 2010 Chevy Aveo and the AC is not blowing cold air. I borrowed the gauge kit from AutoZone and got the following readings with the AC running and the compressor clutch engaged: low side pressure around 90psi, high side pressure around 150psi. Based on ambient temperature around 95F I think that high side pressure is a bit low.

Pressures with the engine off were around 105 on both sides.

From my limited understanding of the system I was initially thinking the expansion valve is faulty. My logic being that that's the "barrier" between the low and high sides. But then I read somewhere that if the expansion valve is stuck open then liquid refrigerant would do directly to the evaporator and cause freezing.

So getting to my question...does anyone know what would cause my low side high, high side low issue?

Thanks in advance,
Peter

[PeterW76]

Thank you for the very detailed reply. I appreciate you taking the time to write that. Clearly I have some more studying to do!

My initial, basic level thinking was that the exv must be stuck open, allowing the high pressure to bleed through to the low pressure side hence the pressure readings I was seeing. But I think I seriously underestimated the complexity of the system.

The car isn't home right now but I'll spend some more time over the weekend, check temperatures of the suction lines etc. I didn't notice any strange noises when the compressor is engaged. Also, the compressor stays engaged...no cycling on and off.

Thanks,
Peter

[PeterW76]

One quick question... Wouldn't low refrigerant level result in low system pressure, either on the the low pressure side or just overall? Would it be worth evacuating, checking for leaks and refilling and take it from there?

[PeterW76]

Hi. Hooked the gauges up again today and got 65psi on the low side, 100psi on the high side. I understand that pressures don't mean a whole lot with a variable compressor system but just wanted to see what they were today. Feeling around the pipework I feel only mildly warm at the compressor outlet and mildly cool at the evaporator outlet. Would that support lack of refrigerant charge?

You mentioned to recharge with the compressor off... does that mean I'm relying on the vacuum to draw the new refrigerant in?

Finally, do I need to add any oil prior to recharge?

Thanks,
Peter