Fix A/C or Live Without? ;-)

Discussion in 'Gen 2 Prius Technical Discussion' started by Robert John, Aug 13, 2021.

  1. Robert John

    Robert John New Member

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    Right you are – thanks for the correction & comprehensive automotive refrigerant overview. I should have stated: “To my knowledge, R134a was phased-out at the retail-level in Canada, although it can be purchased & shipped from some U.S. retailers. To my knowledge, the only retail replacement options for Canadian DIY’s are R12a or R1234yf.”
    Interestingly, one mfg claims that “…1234yf has an extremely low leak potential...”
    Q1: Does anyone have any practical experience with this claim?
    Also, it appears that R12a “…will operate with a lower compression ratio, thus improving the operational characteristics of the compressor by significantly lowering high side compressor pressures.” (from a R12a mfg's website)
    Q2: Is it possible that this is why I’m getting 30 psi on the L-side, but only 115 psi on the H-side (vs. the 199 to 228 psi specified in the shop manual for R134a)?
    Thanks again!
     
    #41 Robert John, Sep 6, 2021
    Last edited: Sep 6, 2021
  2. Robert John

    Robert John New Member

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  3. Robert John

    Robert John New Member

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    "slowly roasting the compressor to death"
    When I bought the car, the A/C didn’t work and I didn’t want to risk running the A/C compressor w/o any refrigerant. I wasn't getting a DTC or anything helpful from the [Auto + Recirc (on steering wheel) + Power (on touch screen)] inquiry, so I wandered around the Toyota Prius Shop Manual and found this: (pg. AC 63 - Pressure Switch) "The pressure switch to detect the refrigerant pressure is located in the sight glass side of the pipe on the high-pressure side. This DTC is output when the refrigerant pressure is either significantly low (below 196 kPa (2.0 kgf/cm2, 28 psi) or significantly high (over 3,140 kPa (32.0 kgf/cm2, 455 psi). Then the pressure switch sends appropriate signals to the air conditioning amplifier. The pressure switch has built-in switches to detect high and low pressure and is turned off when either is determined to be defective. The air conditioning amplifier continuously monitors the pressure switch signal after the power switch is turned ON (IG). It stops compressor control and outputs the DTC when it detects the signal indicating that the switch is turned OFF."
    The switch's connector was in good shape, and although I didn't get the DTC, the A/C amp did prevent the compressor from running… so I guess I was very lucky I didn’t roast it.
    As I was charging the system w/ R12a (as per the manual), the compressor turned-on and the system started cooling. But a few days later the refrigerant had leaked-out and the compressor wouldn't turn-on… so I started hunting for leaks with UV & a sniffer.
    I’m the first to admit I know nothing about A/C, so I really appreciate the help I’ve been getting from everyone in this forum to solve problems, and more important, not make things worse ;-)
    Thanks again!
     
  4. ChapmanF

    ChapmanF Senior Member

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    That is sort of interesting. I'm not sure exactly what that means in a system where the compressor's physical compression ratio hasn't been changed. But I suppose it's possible, if "in condensing conditions, the pressure of RED TEK 12a will be lower" (website containing earlier claim), then that lower back pressure may allow refrigerant to exit the compressor scrolls earlier, producing a lower effective ratio.

    I also see that a proper charge of R12a by weight is 40% of the charge of R134a (same website). How much of the stuff did you weigh in?

    I don't really know how Toyota designed the algorithm they use to control the variable-speed compressor. If their algorithm works mostly by finding the minimum speed getting them a target evap temperature, maybe it will adapt well to the different refrigerant. As this is the Gen 2 forum and Gen 2 only has a pressure switch, not a sensor, I guess they can't really be controlling based on high-side pressure.

    That puts me in mind of Tom Lech's concerns about having enough refrigerant in the system to effectively carry lubricating oil back to the compressor. I don't know enough to make predictions myself; I guess it kind of depends on whether the oil circulation has more to do with the refrigerant's volumetric flow rate (which should be about the same) or its mass flow rate (reduced to 40%).

    I see that the same website has this note: "Where a thermostatic expansion valve is used, slight adjustments will ensure the refrigerant is superheated vapor when it leaves the evaporator."

    The Prius does use a TXV, but it is a bit of a pain to get access to, and I don't know that it is adjustable.

    I guess under the Canadian regs, for anyone who isn't committed to a DIY refrigeration research project, the simple option of taking an R134a-designed car in to a qualified A/C shop for R134a recovery and recharging remains very much available, and probably an economical choice if all the necessities and uncertainties are figured in.
     
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  5. lech auto air conditionin

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    You do not need a ( REFRIGERANT ) leak detector

    you need a HC leak detector use for a gas ( flammable gas ) leak detection like the PG&E guy uses it in your house

    This is something every plumber has who works on furnaces and are heaters

    I do work in commercial and residential furnaces or boilers have flammable gas leak detectors.

    if you do not find anything with the UV dye and it all leaked out within a day or two and most likely it’s the evaporator.
     
  6. lech auto air conditionin

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    R1234YF leaks just like all the other refrigerant no difference.

    was that 199 to 228 baced on the ambient temperature ?

    R134 @ 201 psi = 131°F

    propane R290. @ 115 psi = 72°F

    what was the temperature of your liquid line in those circumstances.

    Think there’s something wrong with your charge quantity.

    is there both times the car was at the exact same outdoor ambient temperature.

    The air selector was on fresh air with the doors and windows open.

    car has been running for 10 to 15 minutes stabilize pressure.
     
  7. Robert John

    Robert John New Member

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    OK, here's the 411 on the responses (Thanks everyone!)
    “…the simple option of taking an R134a-designed car in to a qualified A/C shop for R134a recovery and recharging remains very much available, and probably an economical choice…” As mentioned earlier, if I was in the Bay Area, I’d drop the Prius off with Dr. Lech. I took the Prius to a few local ‘A/C Specialists’ and explained that it worked fine when freshly charged, but stopped cooling after a few days (so assumed there was a leak). I received a myriad of responses, the most common being “with Prius it’s usually the compressor” …accompanied by quotes of $100 to $200 to charge the system + 1 hr or more at $100/hr to locate the leak: i.e. $200 to $400 …just to get an estimate. While I had the bumper & grills off it was easy to inspect the condenser & fittings, so for $352.87 CAD I purchased: 2 cans R12a, manifold gauge set, vacuum pump, gas detector, complete set of A/C O-rings + compressor gasket, ND-11 oil, POE oil-charge can, 4 oil testers - taxes, shipping, duty, included. Granted, none of the equipment is professional grade, but everything worked, did the job, and now – with the generous help of the knowledgeable contributors to this forum – my 2008 Prius has A/C.
    “…you need a HC leak detector use for a gas…” I’m using a gas detector rated for R22, R134A, R404a, R410A and all halogenated refrigerants including HFCs, CFCs, HCFCs and blends… and it seems to work.
    “If you do not find anything with the UV dye and it all leaked out within a day or two and most likely it’s the evaporator” With UV & gas detector, I located a leak on the low-side input flange on the compressor (and saw tiny bubbles in the condensate on the flange). With A/C on 'max' & gas probe in air vents (car off, starting, running, turned-off, waiting a while, then starting again) there was no alarm. Ditto for the flanges on the firewall (UV & sniffer).
    “How much of the stuff did you weigh in?” Better part of a R12a can labeled “24 oz (680g) R134a equivalent” (lost unknown amount due to a defective can puncture valve) fed into a system with a resting vacuum of -26 psi.
    “What was the temperature of your liquid line in those circumstances?” Recent system check (done a few weeks after the repair of the leak & R12a charge) at 67°F ambient, A/C on max, recirculate, doors & windows open, car running 20-30 minutes: Compressor in 90.9-92.8°F; compressor out 102.3-104.0°F; condenser in 90.6°F; condenser out 78.0°F (measured w/ laser temp reader). Gauges: H 112-115 psi; L 33.5-34.5 psi; A/C air out 46.6°F (measured w/ wired probe on vent).
    Going back to my original questions: Prius shop manual says L 21.7-36.2 psi; H 199-228 psi (R134a refrigerant, 86-95°F) Sooo… given that I’m using R12a (not R134a), and readings done on 67°F day:
    Q1: Is the H reading of 112-115 psi too low?; and...
    Q2: Should I be adding anymore R12a? In one chart, for 104°F it equivales 133 psi of R134a to 122 psi (bubble), 99 psi (dew) of R12a – although I have no idea what ‘bubble’ & ‘dew’ means. But that's still way lower than the shop manual's 199-228 psi.
    Thanks again everyone, this forum rocks!
     
  8. ChapmanF

    ChapmanF Senior Member

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    Did your equipment purchases include a cheap electronic kitchen scale to put the can on?

    If a Gen 2's specified R134a charge is 450 grams, and the equivalent R12a charge is 40% of that, 180 g is what I get.

    Are you on a mountain? -26 psi sounds like a kind of lackluster vacuum.
     
  9. lech auto air conditionin

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    112 psi to 115 psi for a 67° ambient sounds normal. Since I’m in San Francisco 67° is just about a daily average.

    If you see the majority of my Prius videos on call days that’s about the high side psi you would see.

    26 vacuum that’s barely nothing that any vacuum pump that would barely be considered a vacuum pump more like a bicycle tire pump that you pump by hand and you just hook the hose on the vacuum side.

    just by sucking through a hose you could pull a 15 vacuum with your mouth.

    since you’re using a laser pointer I can’t trust any of the temperatures so I can’t comment to anything that have to do with temperature to pressure relationship.

    I can tell you the suction line going back to the compressor with a clamp on thermistor type directly clamped to the section line will read somewhere in the low 40° degrees below 50° on your return temperature to the compressor

    I will tell you 21 psi on the Prius is not very common on the low side. It may happen but rarely under certain circumstances.
     
  10. Robert John

    Robert John New Member

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    A) Yep, I’ve got a good digital scale – didn’t occur to me to measure the refrigerant before use, mea culpa. I just added small amounts of refrigerant until the specified psi max was achieved on either the L or H side… whichever came first. d’Oh! I measured the weight of the POE oil can, but I don’t have a reliable way of measuring the amount of lubricant in the system (those little oil measuring cartridges are hard to read) so I’m not sure how much oil I need to add… if any. B) Well, it took a lot more R12a than that to get the requisite pressure on the L side... most of an entire can. I don't know what that implies. C) I’m at 1200’ above sea level. It's possible my vacuum pump sucks ;-) I noticed most gauge sets only go down to -30 psi, so I didn’t think -26 psi was too bad. Could be the vacuum pump, could be the hose(s), could be the gauge. I’m going to connect the pump directly to the gauge and see what happens.
    It's possible my vacuum pump sucks ;-) I noticed most gauge sets only go down to -30 psi, so I didn’t think -26 psi was too bad. Could be the vacuum pump, could be the hose(s), could be the gauge. I’m going to connect the pump directly to the gauge and see what happens.

    Q: What is the preferred vacuum for evacuating an automotive system? For setting-up a mini-split home A/C it's only -76cmHg.
    Thanks again everyone for the feedback & advice - much appreciated. I'm learning a lot here!
     
  11. ChapmanF

    ChapmanF Senior Member

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    -26 ... errm, we both typed psi there, didn't we. I assumed you meant inch Hg without even noticing. -26 inHg is a vacuum, but not an HVAC-quality vacuum. -26 psi isn't even possible (on land, on earth ... maybe on a submarine?)

    Those kinds of readings (called 'gauge' readings) have negative signs because they are what you see on a gauge that reads zero when it just sits on the bench. That zero is really atmospheric pressure, which is about 14.7 psi really, or 29.92 in Hg, or 76 cm Hg (maybe more often written 760 mm Hg). As you pull a deeper vacuum, your gauge reading goes further negative. -26 in Hg is a decent engine manifold vacuum, say, or you could easily use it in a suction cup to pick things up with, but you can see it's still almost 4 in Hg away from being true vacuum. Also, measuring downward from atmospheric that way is a little fuzzy, because atmospheric pressure changes, say if you're on a mountain, or a storm is coming.

    HVAC vacuum will often be measured on a micron scale ... millionths of a meter of mercury, and measured upward from true vacuum instead of downward from atmospheric. So it doesn't depend on your elevation or weather. True vacuum is zero microns. Normal atmospheric is 760,000 microns (I don't think any real micron gauge even reads that high). A gauge reading of -26 in Hg is still around 100,000 microns.

    Toyota's Gen 1 Prius manual specified evacuating to at least -750 mm Hg (which would be 10,000 or lower on a micron gauge), and I bet Tom probably evacuates to the low hundreds of microns.
     
  12. Robert John

    Robert John New Member

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    OK, got it: the minus part of the psi scale is not psi – it’s inches of mercury. So when I was reading the minus section of the gauge’s psi scale it was -26 inHg, or 660 mmHg …12% short of the 750 mmHg prescribed in the Prius manual for evacuation. Do I have that right now?
    Thanks for the primer on vacuum – very helpful.
     
  13. ChapmanF

    ChapmanF Senior Member

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    I think that sounds about right. I have to say, though, that the Gen 1 manual was the last one where I have seen Toyota specify a vacuum figure, that's where I saw that -750 mmHg figure, which is still about 10,000 microns.

    In Gen 2 and Gen 3 they've definitely changed to only saying "perform vacuum purging using a vacuum pump." They don't give a level, they just expect the tech to know that. Most techs would probably scoff at even a 10,000 micron figure. I am guessing Tom probably evacuates systems to low hundreds of microns, not ten thousand.

    Whether it's "12% short" depends on which end you do the math from. Remember, these figures you're looking at are counted down from atmospheric. 750 mmHg is some distance toward vacuum, and 660 mmHg is 12% less than that distance.

    But if you turn around and count up from actual vacuum ... Toyota's -750 mmHg figure is about 10,000 microns, and the 660 mmHg you achieved is about 100,000 microns ... 900% too high.

    Changes the perspective, no?

    And most techs would probably call even 10,000 something like twenty times too high.
     
    #53 ChapmanF, Sep 16, 2021
    Last edited: Sep 16, 2021
  14. lech auto air conditionin

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    I cannot even imagine only vacuuming down to 10,000 µm I would find that difficult to do such a poor job you would actually have to try. Lol

    I would get scolded and reprimanded when I used to work for automotive shops by the service managers and by the service writers for attempting to use metric and all my measurements I was taught by my father and school in math and science don’t even think about mentioning pascals or micron .

    I converted over to digital gauges about 20 years ago so using analog gauges to me is like having to crank start your model A Ford.
    They are massively inaccurate go out of calibration often and their accuracy is only good in their middle range of their numbers scale.

    Yes often always pull down into the low hundreds of micron with a vacuum pump is very easy unless the system is severely contaminated with moisture.
    Severely moisture contaminated system and your vacuum pump will start stalling out at rest somewhere above 2000 µm to around 3400 µm

    If you leave your vehicle on the vacuum pump overnight it’s easy to get below 100 µm

    My father introduced me to a micron gauge at the age of 12 it ran off of six or 8D batteries it had an analog needle you had to let it warm up for five minutes and it took about another five minutes of calibrating procedures to get it working at a starting point. And it was in a rawhide leather case.

    Micron gauges have advanced a long ways since the 60s and the 70s

    using analog gauges is like going back to old bias ply tires with inner tubes on cars mono single cylinder oil filled shocks on your car and you might as well throw on some leaf springs and a front I-Beam axle with king pins.

    Let’s not forget all that fun we had packing wheel bearings
     
  15. ChapmanF

    ChapmanF Senior Member

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    I even had a tool called a wheel bearing packer, whose main distinguishing feature was that it was 100% ineffective on any of the styles of bearing any of my vehicles actually had.
     
  16. lech auto air conditionin

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    I had one of those to
     
  17. lech auto air conditionin

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    I think I have an economical answer.
    A 20 pound cylinder propane in your trunk hooked up to a long hose under the car to the low side fitting on the suction line.

    every time you feel the duct dash temperature starting to get warm you open up the valve until you feel cold air come out of the dash and just perform this task the exact same as if you had a slow leak in your tire and you keep filling it up every couple days.
    Buying 20 pounds of propane for the barbecue is a lot cheaper than the little 5 ounce can of the over price 12a HC
    Probably 1000 times cheaper.
     
  18. Anita24

    Anita24 New Member

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    She has a leak. Evaporator any idea the cost for repair?
     
  19. lech auto air conditionin

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    Around $1500 plus or minus a few hundred dollars depending what part of the country or state you are located.

    Just the labor alone is 7.5 hours to get to the evaporator so you can multiply that by the shop labor rate

    Here in San Francisco California mechanical shop labor rate for an independent garage is usually somewhere between $150 an hour to $230 an hour.
    Dealership rate will usually be higher than that
    Multiply that by 7.5 hours

    Plus replacing the desiccant material in the condenser that may tack on an extra half hour labor

    so a few hundred dollars for the new evaporator new desiccant material and while you have the expansion valve out and off on the evaporator highly recommend just replace it.
     
  20. ChapmanF

    ChapmanF Senior Member

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    I once drove a vehicle to a shop with pretty much everything removed but the steering wheel and driver's seat, to minimize the labor on their end (and maybe also a little because I trust myself more to get it all back together right).
     
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