04 prius AC intermittent cool

Have you checked the codes on the car?

 

Honestly, you need to have the AC system evaluated by a qualified AC Mechanic. AC is one of those often expen$ive repairs that is VERY tempting to turn into a DIY project... generally winds up being more costly to get it fixed correctly after a DIY event.

Right off the bat, your low side pressures are out of spec - how did that happen? I'd bet at some point in the past, "AC Service" was performed incorrectly.

 

The AC system repair price is horrifying. Mine was $2600 last year. A lot of the AC shops around me didn't want to work on my Prius because they were scared of electric shock. They need to have special gear and materials.

 

Bring the low side pressure down to 30 psi and see if that helps.

 

Well yes if there's no air across the condenser the compressor will run very hot.

Probably the condenser just needs a good cleaning. Buy 2 cans of coil cleaner at lowes and take the black plastic cover off the rad so you can get to the front of the condenser and hose it down with the cleaner. let sit and then hose out. Probably bug clogged. Also make sure the bottom FOD cover is on below the condenser or it will take a beating from road debris. You can tell if you take the black plastic cover off and look down if you see pavement its missing.

And the e-coil under the dash needs routine cleaning also.

This is basic AC maintenance for both car and home..

 

As expected.

So the AC vent temp is ambient -35 while driving and ambient -20 when parked. Clearly a condenser airflow problem.

The compressor operates at a speed that is not related to that of the engine or vehicle. Why are you proposing removing refrigerant from the system? The mass of refrigerant is proportional to the BTUs of heat it can extract, less is less.

Fix the condenser airflow problem.

 

Because the low side pressure as measured by the OP (40-50 psi) exceeds the spec (22-36 psi) considerably. More refrigerant is not necessarily better if the refrigerant can't change its state from liquid to gas.

I've found that a tiny change in the refrigerant charge can make a big difference in the performance of the system.

The high side spec is 199-228 psi and the OP also measured more than that range.

It is possible that there is excessive moisture in the system and the expansion valve is freezing up, thus causing the temporary stop in AC function that the OP reported in post 1. So if bringing the refrigerant down slightly doesn't help, the OP probably needs to visit an AC shop for them to pull a vacuum on the system, then recharge. In that case he should visit a Toyota dealer or an AC shop that understands the Toyota hybrid AC system will not tolerate regular AC compressor oil.

 

He's got a bigger issue than clogged condenser. Vent temp at 50 sucks. Down here he'd be sweating. Got to be really cold to do anything.
Pats right get it to a good ac shop that does Prius the guy that said your condenser is not right..

Never mentioned miles on the car.

 

Patrick, with all due respect, both are caused by lack of condenser airflow. The whole system works on "change of state" and if you cannot remove enough BTUs from the HOT GASSEOUS refrigerant as it passes thru the condenser, ALL your pressures will be out-of-spec; even with the correct charge mass.

AC is not to be trifled with, it has confounded some of the best mechanics I know, because they never accepted the change-of-state requirement.

 

Register temps of ambient minus 35 to 40*F is AWESOME performance, especially since he's in the tropics! Unfortunately, he only achieves these while he is driving.

 

I took the attached two photos in July 2010, with my 2004. Looks like 60 degrees F difference between ambient air vs. register temp, to me. I'm using a Fluke 62 mini handheld instant read thermometer. I would not accept 40 degrees F difference as being satisfactory.

 

The problem with IR temperature readings is that they vary considerably based on the color of the object. You are also in the desert, while the OP in the tropics, humidity makes a HUGE difference, because condensing the moisture from the air takes a tremendous amount of energy out of the system.

The industry standard is to use a physical thermometer, I have four and even then, temps vary between registers

 

Time to seek professional assistance, then. Also, check to make sure the radiator fans are blowing air towards the engine.