[barton1976]

2012, Sienna, base, v6.
The A/C usually could start when the engine is cool, then doesn't work if I ever shut the A/C off, or when the engine is restarted.
I observed below:
1. The clutch can always engage when I jump the relay, so it is good.
2. If I don't jump the relay, the clutch doesn't engage when I turn on the AC, if I tried to use it when the engine is hot, or need to use it the 2nd time of the day.
3. Since, it starts sometimes, and I also have another relay to replace to test, I think the relay is OK, as it changes nothing with another relay.
4. When it works, the lower side is about 40 or 41, condenser fan works, clutch engage. I don't have a gauge terminal to test higher side yet, but don't feel the higher side pressure is an issue.
5. Wired thing here: I have seen, clutch engaged, condenser fan stop, and compressor not work as the lower side is about 65 to 70s, meaning, even clutch engage, the AC could still be stopped by something else.

What to check next?
I checked the manual, looks only higher side has the pressure sensor. However it doesn't look like I can play jump trick on it. Anyone has experience to test the pressure senor on 2012 sienna? See the sensor manual captured below.

 

[barton1976]

After I posted this, I read another post about AC compressor flow sensor. So, I tried. The AC kicks in immediately when the magnetic piece moves close to the sensor. Now, the only thing left was that I am not sure if it is going to be the case when the engine is hot. I will try tomorrow when my wife drive back from work, when the engine is hot.
Thanks Patchman's post from last year. I am excited, and will update tomorrow.