The AC on our Toyota Sienna (2007, 167k miles) just stopped cooling suddenly. Worked great last week, with vents blowing like 25F below intake temp. On Friday, wife says it suddenly quit cooling. Yesterday (Saturday) it blew cold for about 3 mins, then only 2F below intake.

I hooked gauges up, high side is 90psi and low is between 55psi and 75, depending on how long the units been running. I vented some coolant off of low side until it read 45 Psi, but it gradually built back up to 75 psi.

So here's my question:
Is there any way this is something (filter, drier, evaporator) besides a compressor? My googling says this is compressor, but I am a true rookie at trouble shooting AC issues.

Sounds more like a leak.

If the expansion valve is stuck open the delta pressure across the compressor can look like that. But depending on system it may be expansion valve, tube, orifice some are more prone to failure than others. Don't know about sienna but uses to be stuck open expansion valve on the rear ac in suburbans will show these pressures and kill the front ac at the same time. Could clamp off the suction line to rear unit to test. Probably can't do this on typical lines used with r134

To clamp off the line I'd likely need to cut in a valve and close it because all lines are rigid.

This may be the point where I use a real expert? I'm all for DIY to save $ but I might make this worse before it gets fixed.

If it was a leak, wouldn't pressure have gone down (less than 20psi) instead of up (over 55 psi) ? When I last added coolant 2 years it was 40 psi and hasn't moved until last week.

please don't just vent the refrigerant to the air

Is it a single evaporator system? I think the sienna is van don't know if it has dual ac. If valve is stuck open you will have little pressure differential across it and likely no temperature differential. Some guage sets can measure sub heat or super cooling and get an idea if there is any expansion in the circuit

It's a single evaporator.

You'd think, but there's a chance that the line will freeze and restrict the flow of coolant if the low side gets too low.

I saw over-pressure conditions on my Mustang and thought the thing was overcharged or blocked. The evaporator core was leaking. The extreme delta p was causing the low side to pull in humid air and freeze which caused a block and high pressure. ...counterintuitive.

You need to take it somewhere


The pressure equalizes when off. You probably have a leak and the low pressure switch is disabling the clutch so its staying at equalibrium. You could observe the clutch and see, but since you think your car is generating its own refrigerant you need to bail on this challenge

Thanks, makes sense.

Thanks!

Quick state of charge can be found in the boiling point temperature/pressure charts for the refrigerant type (134 in this case). Systems typically are charged so in the non operational equalized pressure is such that it's just high enough to keep the refrigerant in the liquid phase. The t/p chart for 134 is close to 1:1. So I would expect the pressure should be close to the air temperature after sitting overnight or for several hours. Much above over charged less low on charge.
Getting 134 to the solid phase is not possible here basically it freezes at ~-100c. It is for sure possible to freeze water and cause strange pressures sure to impeded airflow.
I did look quickly at Rock Auto and it does indicate that Siennas (at least some configuration) have rear expansion calves in addition to tvs for front system(combination expansion and suction throttle valve)

I speak just enough AC jargon to have understood almost none of what you just said.

Alright, paid a monkey wrench (firestone) $930 to diagnose, drain, swap out the compressor, and then refill. Still isn't cooling. Just picked em by price, so I probably got what I paid for....

Worse yet, main engine's temp's running hot. Used to stick stead at 4 out of 10 bars (I think that's like 180F), but now it's running 8 to 9 out of 10, so like 230F. I'm about to do a themostat swap, coolant flush, and refill by flashlight.

I'm going to take it to a more-reputable AC mechanic tomorrow.

This has got to be an expansion valve, right?