What Kills Prius Compressors ? How to prevent it !

Discussion in 'Gen 2 Prius Technical Discussion' started by lech auto air conditionin, Jul 31, 2020 at 11:18 PM.

  1. lech auto air conditionin

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    What kills a Prius compressor is really simple to prevent. Heat!. What kills transmission fluid? Heat !. What kills an engine ? Heat !. So will lack of lubricant.

    As your refrigerant level gradually and slowly gets lower. So does the return of refrigerant oil and so does the return of a cool supply of refrigerant over the electric motor windings that gets very very hot. Some of the Prius compressors later models put the inverter on the top of the compressor which gets very hot on its own not even mentioning the heat from the windings of the motor. And they both rely on a cool fresh stream of ample refrigerant to return to cool them off to extend their life.

    In the YouTube link below I show a Prius compressor and the temperature of the discharge line at 190°F plus. One thing most technicians don’t know whatever the temperature of the discharge line outside of the compressor the internal temperature at the point of compression on the surface of materials where the lubricant i’m bearing surfaces is between 50°F to 75°F higher than the external discharge temperature. Most refrigerant oil start breaking down at 230°F This is about first grade math I think you could see the picture that’s about to happen.



    The static resting pressure on the gauges was 42 psi When I connected my gauges.when I connected my gauges. some people say the low pressure switch on a Prius will protect the system from running when it’s out of refrigerant.

    At 42 psi with the ambient temperature around close to 60° that means there was absolutely no liquid refrigerant in the system it was just vapor left. But yet the system we’re still allowed to operate this is normal do not believe what others tell you about the low pressure switch cutting off the compressor when it’s low on refrigerant. This is normal.

    You will also notice the high side pressure was 60 some odd psi plus with only 3 ounces roughly refrigerant in the entire system. I released a video about two days ago on a 2012 Prius C that I just recharge to factory specification of 420 g took it out on a road test with live Bluetooth sensors connected up to the pressure ports and temperature sensors on the refrigerant lines. Driving the Prius with the air conditioning on max position for fan speed as cold as possible and the high side pressure was only 66 psi and this was normal for this vehicle under these operating conditions.

    I also immediately pulled over the vehicle after driving for a few minutes with the camera still running opened up the hood and showed you the site glass for the refrigerant was all bubbly and barely flowing the majority was air with very little liquid refrigerant but yet the day before I just filled it up with 420 g of refrigerant that is factory specification. Don’t believe the boys who believe in bubbles. They live in a bubble world full of rainbow ponies and unicorns.
     
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  2. valde3

    valde3 Senior Member

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    Can you simply use the temperature of discharge line to determine if the system has enough refrigerant?

    Prius workshop manual gives the maximum pressure on a high side as 1.57Mpa or 15.7Bar or 228Psi. Would this mean that the discharge line temperature shouldn't be higher than 60c or 140F? Or what would be a good temperature? And how much would the outside temperature effect this?
     
    #2 valde3, Aug 1, 2020 at 1:50 PM
    Last edited: Aug 1, 2020 at 1:56 PM
  3. ChapmanF

    ChapmanF Senior Member

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    Those look like numbers that might have come from a table of R134a pressure/temperature at saturation. But in the discharge line from the compressor it is allowed to be above saturation temperature; after all, it hasn't been through the condenser yet.

    The question is how far above saturation temperature is reasonable. I seem to recall one of Tom's videos on the subject (haven't taken the time to re-watch the one linked here to see if it was this one) showed a car brought in for service and the discharge temp was very high, and after properly charging it was lower by a large amount. The implication might be that if you're trying to decide how close your charge is to correct, just looking at discharge temp is too crude to tell you much—except that if you see a discharge temp that's far above anything normal, you can safely conclude the charge is nowhere near ok.
     
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  4. Mendel Leisk

    Mendel Leisk Senior Member

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    Or similarly, the coldness of the air from the vents?

    We use ours only sporadically, and a couple of years back got it recharged at dealership, due to so-so performance.

    Turned it on about a week back and was happy to see good-and-cold air right off the bat.

    I think semi-regular use is good too; it doesn't like long hiatus?
     
  5. valde3

    valde3 Senior Member

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    Yes that temperature seems too low. But wouldn't the discharge line temperature be a good way of telling you that charge is low enough that your compressor is in danger.

    Yes temperature of air from vents can be used to determine something about charge. But based on the OPs post and video it would seem like a discharge line temperature be better way to determine charge level without pressure gauges.

    Yes that's the bad thing about AC. It's needed for cooling for maybe a week a year or some years not really at all. It's useful in demisting for maybe a month. And can't be turned on for almost half of the year as it doesn't work in cold.
     
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  6. lech auto air conditionin

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    Completely ignore all the pressures and temperatures and if you fill up exactly by Weight only everything will be perfectly OK. Absolutely cannot go wrong if the weight is correct
     
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  7. ChapmanF

    ChapmanF Senior Member

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    There was more information on what's in the ballpark in these two earlier videos, also by Tom:





    Where you wouldn't expect the condenser to have to drop the temp by more than 50℉ and, in a Prius, more often 30 or 20 (first video above, 0:40 to 0:60), that particular 2008 was feeding 201℉ vapor to the condenser and getting 84℉ liquid out, making the condenser drop it by 115 degrees. Post-recharge (second video), the vapor was closer to 91℉ to the condenser and 76℉ liquid out, so just a 15 degree drop.

    So while you probably wouldn't want to use such a crude metric to make subtle judgements about a nearly-OK system, it does look like if you see discharge temps higher than expected by a hundred degrees or that the condenser is having to drop the temperature by five times as much as you expect, that would be a pretty clear signal that the system is not nearly OK and you should stop running it, and go pay a visit to Tom or the local shop.
     
  8. valde3

    valde3 Senior Member

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    I was thinking it more as a way for the owner of the car to determine if there's enough charge in the system to run it. Of course the system is just filled up by weight.

    So a maximum temperature of discharge line and/or a maximum temperature drop in condenser for a correctly charged system would be a very useful value. Maybe even as a chart with how outside temperature would effect it.

    Seems like that would be a lot better way than just measuring how cold of an air AC can blow? And there isn't really a number for that either?

    So a condenser temperature drop might be the best metric to determine if there's enough charge. Could somebody give more accurate value on when you would be sure that it's not good?

    Unfortunately whenever you need AC for cooling it's very hard to get anybody to work on your AC. As everyone is trying to get there AC fixed.

    So basically a temperature value or a chart might be able to used to determine if charge is enough that system can (probably) be safely run. Or should you stop running it and book a time for AC work.
     
    #8 valde3, Aug 2, 2020 at 12:05 AM
    Last edited: Aug 2, 2020 at 12:20 AM
  9. lech auto air conditionin

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    Your last paragraph answers all the questions.

    there are so many variables to take into account this is the reason why so many people get it wrong even if they try or even attempt to use a chart for pressures or temperatures.

    Most of the charts were developed back into years when we had fixed speed compressors not variable. Because the individuals who write the news articles magazine articles books and old technicians come from the old school days they keep attempting to try to use old-school methods on modern vehicles and they keep just re-printing all printed stuff because it’s simpler and easier.

    The condenser temperature drop method that you’re talking about is for determining other things.
    But the condenser sub cooling is for calculating refrigerant charge on a expansion valve system.
    you use superheat method if it’s an orifice tube air conditioning system.
    But on today’s cars with the variable compressors and variable condenser fans you can throw that out the window. You’ll be chasing movie numbers all the time the manufactures do not provide software that you can put a hard lockout you set the vehicle in a test mode where it would take over and manually set the engine speed or the electric compressor speed to a fixed speed that would not vary. Then set the evaporator to a fixed speed. And set the condenser fan to a fixed locked in speed. Then you can develop a pressure temperature chart that technicians can follow when the vehicle is put into this test mode that would be activated for testing only.

    In Toyotas Techstream they do this they have a air conditioning test mode you can access to the software I have a video on this on my YouTube channel. Anybody who works on Toyota Prius knows this. Toyota software takes over controls all the system and air conditioning compressor speed the fan speeds it uses all the temperature and pressure sensors with their built in math algorithm software for figuring out whether the air-conditioning system is charged correctly or not.
     
  10. valde3

    valde3 Senior Member

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    So your talking about refrigerant gas volume check. I don't think that test is available in a gen 2 Prius. I don't think that I've ever seen that under a utilities in a gen 2 Prius. Or am I wrong?

    I think the only test in a gen 2Prius related to this is a test to run the compressor at a target speed. But that tests just gives you the temperatures of different components of AC system and rpm of compressor. So without some maximum temperatures it can't even be used to roughly estimate if the system is filled enough.
     
  11. lech auto air conditionin

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    You’re correct not on GEN two wasn’t thinking about that totally forgot.
    I have my own clamp on Bluetooth temperature gauges I don’t need TechStream . And I have my hands my ears and my senses they actually work faster and better than Tech Stream.
    Some of my coworkers who see me work on cars say I’m like one of the religious healing guys just lay my hand on the vehicle and it fixes itself or gives me the diagnosis without equipment. Hallelujah you’re healed
     
  12. valde3

    valde3 Senior Member

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    I was just trying to find if there's way for somebody without a set of gauges to check if the charge is low. If you had to do (a rough estimate on) that what would you base it on? Temperature of air blown into cabin? Temperature of lines? Evaporator temperature on Techstream?

    Figuring the amount of charge from pressures doesn't seem that useful as basically you might as well just empty the system vacuum it and fill it by weight at that point.
     
  13. lech auto air conditionin

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    I grab the suction line before entering the compressor. On a hot day it’ll be nice chilly and cold with lots of condensation dripping off of it.
     
  14. valde3

    valde3 Senior Member

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    So the most basic method. You think that would tell that system probably has enough charge? And of course stuff like temperature, humidity, set temperature and fan speed will effect it.
     
  15. lech auto air conditionin

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    Hot day, all doors and window open, high fan, fresh air mode. Vehicle out in the sun



    This dose not 100% mean there is enough charge but this is a good basic backyard mechanic indicator. Without getting technical and starting to use contact thermal couple temperature probes on refrigerant lines, using delta T method of evaporator temperature drop, Plus you’re high side and low side pressure’s, taking in account ambient temperature, If it’s a accumulator system taking the Delta temperature drop across the inlet and outlet of a accumulator. But most vehicles today we no longer have the easy opportunity of taking the Delta temperature drop across the evaporator because the expansion valves are off to located under the dash.

    But when it comes down to it it’s so easy and fast to recover the refrigerant and recharge it by weight nothing else comes Close or even compares. A two minute to 5 minute recovery time in perfect conditions pulse 60 seconds to fully recharge system with refrigerant.

    Why would I want to go through all that trouble of hooking up gauges and taking readings doing math unless I was looking for a problem. Or wanting to confirm that the system is working correctly.

    In the 2 to 5 minutes it took to recover the refrigerant you will immediately know whether you’re full or you were Low or empty by Weight after that you can perform your diagnosis. It’s either yes or no.
     
  16. valde3

    valde3 Senior Member

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    Yes. I'm just trying to think of a way for backyard mechanic or a small repair shop that doesn't have gauges to figure if it needs to be sent somewhere to be charged and/or diagnosed.

    If you have the gauges then of course you can just vacuum and fill it up by weight. But even smaller shops might not have machine to do that. So all you can do without is to check temperatures and the info available with scan tools.
     
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  17. ChapmanF

    ChapmanF Senior Member

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    A lot of this seems to come down to the idea that there can be tests that aren't symmetrical in their false-positive and false-negative rates. A test can have a specificity higher than its sensitivity, and it seems like for car A/C we have a lot of those.

    So with the discharge temperature or condenser drop, it may be pretty easy to say look, if that's a hundred degrees too high or if that's five times what you'd expect, dude, there's a problem. But trying to pin it down further to "ok, what number would tell me there isn't a problem" would be demanding more sensitivity of the test than it's capable of; you might pick some threshold X and Tom could still rattle off various ways you could see < X and still have some problem.

    The other aids we've got for judging the system condition seem to be kind of the same way. If you look in the sight glass and it looks pretty much the way the manual says it should, Tom could still list off situations where that wouldn't mean everything is necessarily ok. On the other hand, if the temps are mild and all the test conditions are right and you're just seeing gobs of foam, that's telling you everything is not ok.

    Or if a manifold gauge set is showing you pressures that all look about right, that might not be complete independent proof that there aren't any problems. On the other hand, if you see pressures that are way wrong, you'd be wise to conclude there is some problem.

    Some tests are just like that.

    In principle, when you have three different high-spec/low-sens tests like that available, you can use them in combination and give yourself better confidence. In casual terms, it makes sense that if you've got three things you can check that are better at revealing a problem than convincing you things are ok, and none of the three reveals any obvious problem, you might feel better that things might be ok than you would with any one of the tests by itself.

    More formally, if you had good statistics on the true and false positive and negative rates of the three different tests independently, you could figure out what they should be for the three tests together. But that's more likely to be seen in a classroom than in a working shop, where probably nobody's taking the time to collect those statistics.
     
  18. Mendel Leisk

    Mendel Leisk Senior Member

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    that kinda reminds me of my tire air pressure gauge collection: ill try them all on one tire; they're all pretty close except for one that's 3 pounds higher? I rely on the consensus of the rest, assume the outlier is wrong.

    OTOH, there's the Twelve Angry Men syndrome...
     
  19. lech auto air conditionin

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    If they are legitimate shop and they don’t have gauges they should not be touching AC PERIOD !!!..... now we’re gonna start using the word HACK ! and BUTCHER !. Starting to sound like the same kind of shop when the transmission burns out they get a new transmission or wrecking Yard transmission but don’t flush out the transmission cooler that has the metal flakes in it from the burnt one or the old torn converter and they put it on charge the customer and only last 30,000 miles and burns out again.

    We are motor shop with no gauges those are the guys when they accidentally overfill it and it starts blowing out the refrigerant out the pop off valve on some vehicles releasing refrigerant to the atmosphere. When they need to change a part they don’t own equipment they just open up the line and bleed the refrigerant to the atmosphere. Those are not shops those are animals of a lower human species.

    OK now I’ll come down and get back to the question.

    Because the Prius has a electric compressor unlike most of the cars this is an added heat load.

    There is a situation where when you have a lower charge at a certain point the pressures that were falling and going down start going back up again. It is a situation when your overcharge in the pressures go up again. And yes the more heat there is outside the more heat there will be in the system to dissipate through the condenser.

    Trying to put one formula for all cars is not possible. Remember the vehicles with the fluid thermal fan clutch that fan clutch holds it calibration pretty well usually within the first 30,000 to 50,000 miles. After that it doesn’t work so well and you just starting to lower the airflow over the condenser this will mess with all your numbers and you will be off.
    Then you’ll have guys who don’t understand the systems with fans that pulse the fans with a constantly moving target of pressure that’s bouncing up and down as a say for example the fan pulses on when the high side pressure hits 230 psi keep the fan on until the pressure on the high side falls to 150 psi turns off and repeats so fast that you can never use the pressures to determine what is right and what is wrong. Then you’ll have guys who don’t understand the systems with fans that pulse the fans with a constantly moving target of pressure that’s bouncing up and down as the sea for example the fan pulses on when the high side pressure hits 230 psi keeps the fan on until the pressure on the high side falls to 150 psi turns off and repeats so fast that you can never use the pressures to determine what is right and what is wrong.
    Been vehicles with fluid driven fans remember the infinity with what looked like a power steering pump but actually drove the fan at different speeds this constantly moving your target temperature or pressure.
    Then there are the two fans on the condenser we’re only one works until a certain pressure and then as your steadily lean out and it keeps raising then the second fan kicks in.
    And there’s other variations so many other things that can affect your pressures and temperatures. Usually everybody just wants one way of doing things simple and short and then they apply it to everything and this is where all the mistakes start to happen. Human beings are naturally lazy and look for the easiest method.

    That’s why it is nice that Toyota has their AC volume test under tech stream software. That’s only in the later versions of vehicles but since the majority of the mechanics at Toyota know nothing about air-conditioning they could just hit a volume test button and be in the ballpark as good. But it’s faster and easier to just drain the system fill it up charge the customer and make money and push it out the door. The guys at Toyota or on a bonus program the more cars they get done in a day and more billable hours the more money they make and then you have the s Service advisor on their little bonus their hand is in the piece of the pie. And there is a shop manager who is under pressure by the owner or higher ups to make the numbers profitable he gets his little bonus at the end of the quarter.

    If you did only one vehicle one model one bike and you try to apply pressures and temperatures that never change yes then you can do this. You were able to be able to map and graft every ounce of refrigerant over a wide range of temperatures and come up with a pretty good fixed chart that you could apply to every vehicle of the same year the same make the same model under the same conditions.

    Oh yeah I remember those guys don’t check the cabin air filter that throws your numbers off when they’re dirty even partially dirty.
     
  20. valde3

    valde3 Senior Member

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    Of course a shop without a gauges can't touch AC. If they have no gauges they have no way of filling up the system and probably no personnel qualified to work on AC. And without a qualified personnel and machines there shouldn't even be a way for them to buy the refrigerant. Also releasing the refrigerant would be a crime. But those places might be checking a vehicle over and seeing if it needs work so if there would be a method to check if AC is working good they could do that.

    Exactly because of your talk about Prius AC system being different than old systems I thought that you might be able to tell some ways without a gauge set to determine if the charge in a Prius system is (probably) enough. But it seems like it's not that easy on gen 2 Prius.
     
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