Anyone with FSM 95-97 - need A/C pressure.

Discussion in '80-Series Tech' started by IdahoDoug, Aug 8, 2005.

  1. IdahoDoug

    IdahoDoug

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    Was running errands with my bro in law and he needed a bulb for his 80. While waiting at the auto parts store, I noticed there were bubbles in my R134 sight glass (anyone else do random stuff while waiting??) so I picked up a recharge canister and guage. Filled it right there in the parking lot. The low side pressure went up from 45 to 55 and the bubbles disappeared completely. Took about 5 minutes of shaking and cajoling the recharge canister to give up its contents.

    Anyhow, notably cooler dash output - no question its at least 10 degrees cooler. I'll repeat last week's digital thermometer test to confirm.

    My question is - what's the proper low pressure on the 80's 95-97 systems? I have another canister I can put in, but I'll return it if I've got it to the max. Anyone??

    Thanks,

    DougM
     
  2. Rookie2

    Rookie2

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    I don't know jack about AC charging, but if I interpret the FSM correctly, under the "Refrigerant System Inspection with Manifold Gauge Set" section of the 97 FSM, it looks like under the operating conditions it list, for a normally operating system, the low pressure side is 21 to 35 psi.

    :beer:
    Rookie2
     
  3. IdahoDoug

    IdahoDoug

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    Hmm, that seems very low. It started at 45psi when I put the guage on it and it had basically foam going past the sight glass. Also, there should be a different system PSI listed for each level of ambient temperature. To wit:

    70 degrees - 40-45psi
    80 degrees - 45-50psi
    90 degrees - 50-55psi

    etc, etc....

    I wonder if it's the "Manifold Guage Set" that is the issue. It could be this is an entirely different way to measure the pressure. I did see such a set for sale there, but it was $90. Mine's a simple pressure guage straight off the low pressure fitting.

    Thank you, Rookie2 - appreciate the info and time. Any further reading show another pressure or series of pressures??

    Anyone??

    DougM
     
  4. Elijah

    Elijah

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    Don't know the factory specs but just charged mine 3 weeks ago and when finished read 64-65 psi. Seems awfully high compared to those fsm specs. Absolutely no bubbles in the glass either. Hope it helps.
     
  5. cary

    cary

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    Doug,

    I am suprised and ashamed at you. Charging an A/C by low side pressure is like determining that you need to pee by checking for skid marks in your shorts. Low side pressure is only used in diagnosing problems, not for setting system pressure.

    You need to buy a high side guage. You can get a single one for about $20. High side pressure should be approximately 2.2 times the ambient temperature in F. If I recall the LC is slightly higher, so use 2.4.

    Note: 1) It is normal for a R-134 system to have bubbles in it, 2) The type of kit you picked up is notorious for overcharging and killing R-134 systems, and 3) R-134 systems work best slightly undercharged, the opposite of R-12 where a slight overcharge works best.

    I would recommend checking with a high side guage and if necessary bleeding off some pressure.
     
  6. cary

    cary

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  7. IdahoDoug

    IdahoDoug

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    Cary,

    Thanks. I'll do that - worth the long term investment I guess. Still need the 80s specs tho.....

    As for normal bubbles, I noted that my sight glass went through several phases as follows:

    First examined (nothing hooked up or done at all): Solid white foamy passing by the glass port.

    About half the canister into the system: Clear for about 10 seconds, milder foamy for a while in a cycle. Seemed like it would be the compressor cycling, but I was right next to the compressor and it was not cycling in synch with these changes in the sight glass.

    Full canister into the system: No bubbles whatsoever. Sight glass perfectly clear at all times.

    Cary, my guess is you're going to say the halfway cycling was where the system should be, eh??

    DougM
     
  8. cary

    cary

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    I'm not savvy enough to fill A/C by sound. The guages don't lie. :D :D :D
     
  9. IdahoDoug

    IdahoDoug

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    Cary,

    Heh - no I was suggesting that you might know enough about the qualities of R134 to know that it's supposed to remain in a threshold/cycling situation of some bubbling to be at its optimal pressure for transfering heat. "Fill A/C by sound" indeed!! Heh!

    DougM
     
  10. landtank

    landtank SILVER Star

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    I don't think the "80 specs" are any different than the "R134a specs" after all the vehicle the system is installed in has nothing to do with how one should setup the system, the AC is a sub system of it's own. If the "80 specs" are different than that of the :R134a specs" then I'd suspect that the "80 specs" are wrong.
     
  11. cary

    cary

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    Specs very slightly. It has to do with airflow and the sizing of components. In the case of the 80, the pressures are set slightly higher than average because there is no electric fan. No E-fan at idle means less airflow and correspondingly high temperture of the evaporator which leads to higher tems. That is why on the 80 you aim for 2.4 times or so ambient temp rather than the more normal 2.2.
     
  12. RavenTai

    RavenTai

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    From

    http://www.onlineconversion.com/pressure.htm


    Same as what R2 said,

    We are reading gauge pressure here not absolute pressure but the absolute should not skew the results as we are converting from another gauge pressure, not something like:

    1 atmosphere [standard] = 14.6959503 pound/square inch [absolute]




    Here is some info on reading the sight glass, IMO it is only for troubleshooting purposes not servicing the system. Note the test conditions.

    “higher than usual” for GA? ID? or Tokyo?

    And IMO the most accurate way to service the system is by weight, it does not change with ambient conditions (temperature, pressure, altitude, humidity ) and vehicle state (door open/closed, AC control setting, RPM, engine bay temperature etc) also this is the only spec given under SERVICE DATA, servicing by weight does require removing all the old refrigerant and vacuuming down the system and has not been popular with those on this forum in the past.

    Edit, incorrect see post #15 and #17 below.

    Failing that service it by pressure with a full gauge set. Remember to purge the lines to prevent introduction of air into the system.


    I have a coworker that has charged his system by temperature of the outlet air, he slowly adds refrigerant until the temperature bottoms and just starts to come back up, he has added a different compressor and therefore changed the volume of the system.

    Seams to be it would be best to watch all 4 indicators when servicing, in descending order of importance: weight, pressure, outlet temperature, and sight glass.
     
    Last edited: Aug 9, 2005
  13. landtank

    landtank SILVER Star

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    WHen I did mine the guage readings didn't seem all that accurate or constant. It seemed more like a ballpark reading. I only say this as the guage kind of floated, but I was in a cool garage that was warming quickly since I opened the south facing garage door.

    at 70 deg that would be 168 verses 154, from my experience you would be lucky to be within half that range of ideal.

    interesting about the variables of the vehicle, I would have thought it would have been up to the designers to meet the specs of the R134 on their end. But I can see how high side PSI would be influenced by condensor temps.
     
  14. scottm

    scottm

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    Looks like you got what you need here, my FSM says the same. I can fax you pages if you'd like. Doesn't our brother Jeff have AC guages? I need to charge also, haven't ever looked at the charging stuff you used. Should I try the kit or go through the effort of getting Jeff and his guages? They're old, would they still work on new systems?
     
  15. Tools R Us

    Tools R Us

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    The sticker under my hood reads; Max .90 kg, 1.98lb, min .80kg, 1.76lb. Where did "(59.98 +/- 1.76 oz.)" come from? There are still 16oz to the pound, right, or did that change with new math? :D Correct charge is 31.7oz?

    Be careful what you buy as "freon" a lot of the stuff at parts stores has seal sweller and oil in it. You don't want the seal stuff, if you haven't lost any oil you don't want to add any and the oil in most of the cans isn't the correct type for our trucks.
     
  16. IdahoDoug

    IdahoDoug

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    OK,

    So tomorrow I'll check to see that the system shows bubbles immediately after the A/C is shut off, then goes clear. If it passes that, I'll call it good. If the sight glass stays clear, then I've got a bit too much in there.

    Still bugs me that the system pressure is higher than spec calls for - even before I started adding it was 10psi higher than the FSM max.

    Agree with the comments about some canisters having junk added to them. After realizing this, I carefully went back through the various choices and even found one that had mostly oil and just a smidgen of freon even though the label blared "R134 REFILL". I chose the one that had freon as I don't see any evidence of oil leakage in the cursory lookover I did.

    System definitely works better though I'll reborrow the same digital guage tomorrow to verify this subjective comment.

    Scott - come out to Idaho and I'll correctly refill yours with my guage - heh. Actually, hang tight and I'll send it along with the rear axle special tool and save you the $20.

    DougM
     
  17. RavenTai

    RavenTai

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    "(59.98 +/- 1.76 oz.)" is a direct copy paste from the 96 LX450 E-manual (well I did have to add the +/- as it did not copy over into this font) , checked my paper manual and it says 850 +/- 50g 29.98 +/- 1.76 looks like a type O in the e-version :mad: not the first time

    Under the hood of my 96 LX it also says 1.98 1.76 pounds.

    max....., 900 gram = 1.98 pound = 31.74 ounce
    nominal, 850 gram = 1.87 pound = 29.98 ounce
    min......, 800 gram = 1.76 pound = 28.22 ounce


    Thank you for pointing that out. I would hate for someone (maybe me) to put almost twice the needed refrigerant in and blow the compressor.
     
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