No cooling. Low pressures old Toyota Sienna

[russ]

Asking for advice before taking car to the shop. Toyota Sienna 2001. Has front and rear manual AC. Expansion valve type. Has sight glass.

AC very poor cooling for yrs. Nothing done except check low and high pressures with two gauges.

Measurements: US General gauge
Ambient temp 62F
Engine off. Static Low 55psi high 55psi.
Engine on idle speed, ac clutch on. Low 4 high 75
Engine on. Rpm about 1000 car has no tach, ac clutch on. Low 4 High 80

Engine off for 1 min to equilibrate. Low 50 High 50

Measured again: Pittsburgh gauge
Ambient temp 62
Engine off. Static Low 45 high 50
Engine on idle speed, ac clutch on. Low 6 high 80
Engine on. Rpm about 1000, ac clutch on. Low 2 High 100

Engine off for 1 min to equilibrate Low 40 High 45

AC clutch observed to be on by seeing it spinning and seeing moving bubbles in sight glass. Sight glass mostly bubbles. Never gets clear. AC clutch cycled off only 2-3 times. Not short cycling. Stayed on most of time with low pressure. Off at about 5psi, back on 35. But clutch stayed on most of time even below 10 when measurements were done. Have not looked for leaks.

Both gauges checked by measuring different car with functioning AC. Static pressures only and both gauges measured nearly the same.
Ambient temp 59-60 deg F.
US General Low 65 High 60
Pittsburgh Low 62 High 60

Heater blend door works. With cold weather, vent temp is clearly cold at cold setting, hot at hot setting.

Are low readings due to low charge or something else? Blockage?
Why should the clutch be engaged with such low pressures?
What to do? Attempt vacuum and recharge or just take it to the shop? Thanks.

[Cornbinder89]

Sight glass is more indicative than the pressures alone, but both together point to low change. The low side reading when running is what you would expect if the unit was low on charge. High side also, but a low high side can be many things.
Rarely do I see a more clear indication of low charge. When was the last time it was serviced?

[Cusser]

Remember - NEVER add any sealers or refrigerant containing sealers !!!

It's possible that over 19 years your issue is just accumulated refrigerant loss. But the leak may be larger, maybe have a shop add UV dye and refrigerant and check for leaks like a week later.

[russ]

Thanks for replies. Bought Sienna used about 4 yrs ago. Don't have service records. Seller claimed some AC service was done but don't recall when or what was done. AC was cold 4yrs ago. I have never used sealer. How to determine if is low charge or something else? If both pressures are low, could it be due to clogged expansion valve? I think would be possible with an orifice tube system.

Are low price leak detectors like an Elitech on Amazon for about $25 useful or does it take a higher price device? Did Toyota add UV dye at the factory? Have UV light. Will check.

[Cornbinder89]

Sight glass is the key, it is showing vapor in the system after the condenser. It is low, but you can't know exactly how low or how much to add. Best to evacuate and measure the correct amount by weight and recharge. No, it doesn't show a clogged Tx, which would show high, high side and vacuum on the low side.
I would recharge and add dye, if you already have a UV source.