Need help troubleshooting air conditioning

[davislau]

I have a base model 2007, 5-speed Toyota Yaris. Air conditioning was working fine, but one day I got in the car and no cold air. Blower is working, and A/C light comes on.

What I've done so far:

- Tried recharging the system with refrigerant. But the gauge read over 100 psi (> 700 kPa). This is very high, and each time I squeezed the trigger, the pressure went down slightly. I don't know how it can be overcharged because the system hasn't been touched in many years and has been working fine. Does this mean refrigerant is accumulating high pressure in the low side of my system?

- Looked at the sight glass near high pressure port and saw no bubbles. Condition: All doors open, held engine at 1500 rpm, max blower speed, max cool A/C temp.

- Measured low port pressure with engine off. Still read the same high (> 100 psi, 700 kPa) pressure

- With the car at idle, turned on A/C, and turned blower speed higher and higher. Engine speed dropped with each step in blower speed. At max blower speed, engine is shuddering slightly under the load at less than normal rpm. (Usually, my rpm rises when A/C is turned on and you hear a loud fan-like noise from outside. Neither of these happened.

- A/C compressor does appear to be engaged as the disk next to the pulley is spinning. It didn't look like it was disengaged when the A/C was off though. But the engine idle is normal when the A/C is shut off so maybe it is disengaged?

- One day the A/C worked for a few minutes blowing cold air, but stopped working again.

- Felt the input and output refrigerant lines to the compressor. Felt no noticeable difference in temperature.

- No condensation or frost saw on any of the lines.

- Measured resistance between terminals of connector coming out of compressor to be 12 ohms at 70 F. It's supposed to be 10.1 - 11.1 ohms at 77 F

- Checked 3 fuses in engine bay. They were all good.

I'm at a lost now as to what to do. Don't really want to take it to a mechanic if I can help it. Does anyone know what else I can do to diagnose the problem? I still have no idea what it is. I suspect the compressor is bad, but I'm not certain.

Thanks a lot!