Air Conditioner Issue

Very difficult to troubleshoot without measurements of system pressure. And now that you've added refrigerant, the original symptom might get masked.

The dust cap isn't a big deal. It keeps the valve clean and prevents accidental contact from triggering a gas release, but it isn't part of the pressure seal itself.

If you're not ready to take on the repair at home, see if another shop can get you in sooner. The steps and tools needed are going to be the same no matter who actually does the work. Nope, I just educated myself and this is incorrect. Special steps required for Prius A/C, read on.

A manifold gauge set, thermometer and volt-ohm meter are bare essentials for tooling. Factory service guide a big, big plus.

 

Things to consider: If it needed gas before, I guarantee it had a leak. AC systems do not "use up" refrigerant. A good system can last decades without adding refrigeration gas, regardless if its your home, auto or commercial system. If the system is low again, it still has a leak. Finding and fixing the leak is the real solution especially if it's already leaked out after a recent refill just a few months earlier. That's a big leak. Second, when you have a leak, often moisture and air will enter the system creating a situation where just adding gas will not give you the original btu capacity. They should pull a vacuum after they repair the leak. Get a new charge port cap at a dealer or junkyard.

I would find some other shop that can find, repair, vacuum and charge properly.

By the way, refrigerant oil is also lost through a leak. Sometimes you can find the leak by looking and feeling for the oil. A good shop knows to replace that oil as it lubricates the compressor.

The good news is the Prius v air conditioning system is a very good high capacity unit bigger than normal prius systems. It is also an electric driven variable speed compressor capable of full capacity at idle. I live in south Texas and it will cool a hot car down in minutes and require turning the capacity down.

 

The Repair Manual cautions against using gauges that have been used on AC systems with regular oil, say it can cause contamination. I'm not sure how critical that is, and just hope-and-pray the dealership was on the ball, when I brough ours in recently.

 

OK! I was just reading up on this- there is something to it, and I would call it critical because it compromises electrical safety.

I guess that rules out borrowing or renting a gauge set, because you'd never know where it has been and what substances have passed through it. Not having cheap/free access to that tool more or less eliminates DIY possibilities.

From this page I was just reading, Prius air conditioner work is fairly specialized. I would advise the O.P. to wait for existing service appointment.

 

I would not get too excited about oil contamination as an overarching issue. In most cases, "local mechanics" are just adding refrigerant which by itself, usually does not have oil in it. It is a good idea to have a gauge set dedicated for POE oils, which is almost universal these days on newer home, auto and commercial systems. POE is basically a synthetic oil where older systems used mineral oil. One of the downsides of POE oils is their increased vulnerability to moisture pickup. A good shop will replace the receiver drier after they fix the leak. The 134a cans with leak sealant are a problem in these cars and even to some degree, in all cars.

 

The repair manual says you can use a gauge that's been used on regular systems three times at most. Sounds a little iffy, how do you track "uses", and with big bucks riding on contaminated vs not, I would almost want to use a new gauge set every time. Like single-use hypodermics, lol.

I don't want to think about what the dealership used recently, hopefully all kosher. If anything bad happens, hopefully my invoice will provide some leverage, if there was an issue down the road.

(The notice is on next to last page in attachment.)

 

With so much at stake I'm really curious why Toyota didn't adopt a different fitting- opposite threads or something to prevent accidental contamination. It's no big deal for pro shops to get a few more manifolds, maybe paint them with a blaze of dayglo and hang them on the hook that says "prius only". It's not much more to have that set married up to a thread adapter ring or something.

 

Ambient temp affects the operation of every air conditioner. An overcharged unit can show normal pressure on a cool day and danger-high pressure on a hot day- always need to do a temp compensation on the gauge reading.

It sounds like there's a combination of a leak and overcharging. If it were mine I would have the gas recycled, replace the schrader valves and the o-rings on the ends of each of the hoses, then do an evac test. If it can hold a hard vacuum for a few hours, it's ready to recharge.

When you say the temp gauge was in the red zone... which gauge exactly was this? One of your tools or the gauge on the car dashboard?

 

Agree with the above. You have overcharged the system and it's cycling on excessive pressure especially when it's hot. Take it to the dealer.

 

It is fairly specialized ... well, really, I don't know how specialized. There's the electric compressor, and the importance of not wrecking it with the wrong oil. There's the subcooling condenser design, which moves the correct charge quantity from "around when the sight glass bubbles stop" to "100 grams more after the bubbles stop". So two specialized things to know; beyond that, it's an air conditioner.

That's an interesting article; there's good information in it, but also a lot of it is weird. He quotes a diagnostic code "POAG" (several times, not just one typo!) when we're pretty much all familiar with OBD-II DTCs being five characters, not four ... and he's got strange ideas of what the problem to be avoided is.

"If another universal ester or PAG oil is used instead of this special oil, there's a risk that the aircon system is not grounded correctly. A mechanic who is unaware of this and touches the aircon compressor at the wrong moment, runs the risk of getting an electric shock."

Um, errr. That compressor is aluminum and it's bolted rather solidly to the engine block, which is also aluminum and fitted with heavy ground straps. The chance of the compressor being "not grounded correctly" is, mmm, pretty low, as is the chance of it giving you a shock. The thing you're really hoping to avoid is creating current paths between the windings of the compressor itself, until those paths make more heat, more heat breaks down more insulation, more current conducts, making more heat, and the motor burns out.

Having it start with a small leakage to ground is a useful advance warning, because the ECU can detect that.

Then he goes on about testing the compressor itself with an ohmmeter on the "two terminals of the motor". That could, possibly, work on a Gen 2 compressor, where the terminals you can access really are the motor terminals (only there are three of them, not two; it's a three-phase motor). You'd probably want to use a megger, not a regular ohmmeter. And good luck trying the same thing on a Gen 3 compressor. That one does have two power terminals instead of three, but they don't go straight to the motor. The Gen 3 compressor has its own inverter inside, so if you put your meter on those terminals you're just trying to meg out a circuit board.

It reminds me of a sort of article I've seen a few of before, usually on sites that offer to pay contributors some amount for supplying articles of a certain sort, in a certain length and style. The would-be author can have some amount of real, accurate information about something to start with. The editor says "liked your first draft, but we'd like something with more detail and closer to, oh, 1400 words."

So the author sits down and makes up enough more details that sort of sound like they could be true to hit the word count, and pockets the check. I've occasionally seen authors with whole strings of such stuff, where it seems like they've learned the expected style and wordcount and just flat out make up the right amount of BS for the first submission; saves everybody time.

-Chap

 

Thanks for the insight! I've never attempted to repair a prius air conditioner but I've done okay on "traditional" automotive AC diagnostics in the past.

Have I understood this correctly that the electric compressors used by Toyota bathe their drive motor in refrigerant, thus requiring that the mix of refrigerant and oil maintain a certain level of electrical non-conductivity? I can easily picture such a system & requirement, just haven't run into that in a mobile cooling setup. I gathered that the risk was the refrigerant/oil conducting HV from a motor winding.

 

That's more or less the size of it. I don't honestly know how much of the effect is the oil's own conductivity, and how much is the oil chemically degrading the nonconductivity of the insulation coating on the windings. I would think it has to involve at least some of the latter (after all, you sort of hope you could take good windings with their insulation intact and set them on a conductive surface without letting the magic smoke out!), but anyway, the end result seems to be compressors exposed to the wrong oil burn out, and it reportedly doesn't even require all that much of the wrong oil.

-Chap