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A/c hose restrictions

Discussion in 'Shop Talk' started by rmllarue91, Jul 11, 2018.

  1. rmllarue91

    rmllarue91 Senior Member

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    Hey hef I got a redot a/c unit a134 roof mounted . I have a restriction can't find it. Have changed everything but hoses until tomorrow. Condenser evaporator expansion valve 2 driers and compressor
    75 degree air temp high side 200 low side 15 2.3lb charge what manufacturer calls for. We are putting new hoses on it tomorrow but I'm not seeing and cold or hot spots in the lines anywhere. Line coming out of expansion vavke will drop down to 55 degrees and almost 100 degrees line going into expansion valve.
     
  2. funwithfuel

    funwithfuel Senior Member

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    So, what about your condenser? Do you have air flow across it. With a roof unit, does that mean no fan for the condenser?
     
  3. heymccall

    heymccall Senior Member

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    Low side @ 15psi with engine idling sounds like undercharged.
    What started all the throwing parts at it?
    My experience with reddot leads me to believe that the expansion valve comes in different ratings in the same configurations. Could you have put in the wrong one? Screenshot_2018-07-11-18-31-40.png
     
  4. funwithfuel

    funwithfuel Senior Member

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    I would have thought just the opposite . Good air across the condenser at idle we should be like 0-5psi on low and maybe 125 on the high. It sounds like overcharge to me. Maybe even inadequate vacuum prior to charging.
     
  5. Mike L

    Mike L Senior Member

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    Have you flushed or at least blown compressed air through any of your lines.?
    At 75 degrees ambient, 200 seems high and 15 is low.
     
  6. rmllarue91

    rmllarue91 Senior Member

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    I blew through whole system piece by not a single piece of debris was found at least 30 min vac down each time. First trip topped system off. Diagnosed restriction ordered expansion valve and drier... Charge system same 15 and 200 tried over charging just made difference worse. Went over system with non contact thermo couldn't find a hot spot or cold spot rolled dice on condenser internally contaminated same.... Ordered a new evaporator and another drier Same results.... Today tried swamping expansion valve from a Kenworth the customer had on shelf that is a 4.lb system. It made it worse low side is about 10 psi. Now getting new hoses made tomorrow and we put a new compressor on somewhere in between because after all this we don't want that to go bad. It's a Timco 425 feller buncher maybe the dealer sent us a wrong expansion valve? Idk but it's sure is my worst a/c job to date.
     
  7. Birken Vogt

    Birken Vogt Charter Member

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    Those pressures sound normal to me at 75 degrees. You are going to need to measure temperatures more certainly before we can tell exactly what is going on. To start we need to know what the temperature of the cold liquid refrigerant leaving the TXV is and what it is coming back as vapor to the top. This will need to be done with thermocouples and insulation, a point and shoot will not be very accurate but might get somewhere. Also what is the temperature of the liquid once it leaves the condenser at 200 psi once it gets out of the area of the cooling fans.

    Is the clutch cycling when you are doing all this? You should have the temperature switch bypassed on and preferably do it on a warmer day.

    Is there full air flow going THROUGH the evaporator, not around it? Sticks of foam pipe insulation can help with this.
     
  8. funwithfuel

    funwithfuel Senior Member

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    Are you charging by weight or by performance.
    I would pull some air across the condenser and check to see if your pressures drop and performance increases.
    Just got treed by BV, solid info.
    I keep asking. Is there a fan blowing or pulling air across the condenser? Is it tied into the trinary switch ?
     
  9. funwithfuel

    funwithfuel Senior Member

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    Oh, btw what kind of expansion valve do you have? The block manifold or the one with the disc and capillary tube? If capillary style, do you have the bulb secured to the outlet tube of the evap coil and properly insulated?
     
  10. rmllarue91

    rmllarue91 Senior Member

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    Twin fans moving lots of air across condenser panel I charged this both ways with a scale and by performance. With point and shoot condenser inlest 120s out about 100 line going into expansion valve 70s and 50s coming out with the tiniest amount of Frost on discharge from expansion valve.
     
  11. rmllarue91

    rmllarue91 Senior Member

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    Block style expansion like ones pictured above
     
  12. Birken Vogt

    Birken Vogt Charter Member

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    Or spray it with a garden hose, quick and easy. But at 200 psi I don't see how there is much to be gained.

    Also I forgot to ask is there a sight glass to see if there is solid liquid or bubbles going to the evaporator.

    Edit: I looked at the chart and 200 is too high for the condenser after all especially at 75 ambient.

    Correct my understanding if wrong but you are seeing 200 condenser pressure and 100 degrees outlet that is 31 degrees of subcool, indicates overcharge but a garden hose will take care of that temporarily.
     
    Last edited: Jul 12, 2018
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  13. funwithfuel

    funwithfuel Senior Member

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    There's no chance that the oil charge is too much , is there?
    Do the fans run continuously? Or tied through trinary switch? If they're continuous, you're losing air flow across the condenser . That pressure is too high for a cooled condenser. That and you're only shedding 20*.
     
  14. funwithfuel

    funwithfuel Senior Member

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    I know I beat the condenser thing to death. I do that for a reason. Every challenging A/C problem I've encountered and sometimes overheating as well has been tied to poor air flow. Either dams are missing, fans bolted to hubs backwards... all kinds of crap. Once pulled a perfect blanket of cottonweed off a radiator face. Since it was between the CAC and the rad, no one saw it . I know that's not what you have, but the principle is the same.
    Place a rag in front of or behind the condenser will the fans hold the rag against the face? Do they blow through the condenser/ housing or around it. Does the air flow forcefully blow the rag away at the exit side of the condenser?
    BV was spot on with the garden hose. I completely forgot about that as an option. The liquid water on the surface of the evaporator will drop pressures like a rock. If this simple test proves out, you gotta look at airflow
     
  15. Mobiltech

    Mobiltech Senior Member

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    What is the temp at the line going into the evap core? Is the heater shutting off properly or adding heat to the system?
     
  16. rmllarue91

    rmllarue91 Senior Member

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    Condenser has alot of air moving across it and it pushes alot of heat off it very warm air. Didn't try watering it down when I was there. Line going into expansion valve witch is mounted to evaporator is in the 70s can't get to evaporator with system operating.
    The heater hoses are shut off and there is no coolant in the lines at heater box.
     
  17. funwithfuel

    funwithfuel Senior Member

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    Well your diagnosis is textbook correct with an obstruction based on the pressures that you have. However I still struggle with that thought process since you don't have a sudden temperature drop or a frost spot anywhere along the system. I was really hoping that we would find something with poor air flow across the condenser to drop your in your Inlet pressure that doesn't seem to be the case I am all out of ideas I apologize I could not be of more help
     
  18. Birken Vogt

    Birken Vogt Charter Member

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    With the H-block TXV, the TXV opens and closes to maintain the superheat at whatever it is set for. Like the one in the picture is 5 degrees superheat. So if the low side pressure is 15 psi, the vaporizing liquid leaving the TXV entering the evaporator should be 15 degrees F and the vapor coming out the top of the evap, back to the TXV should be 20 degrees F.

    If I understand the problem correctly, the evaporator outlet is more like 50? If this is the case the evaporator is not getting enough refrigerant and you already know to look for cold spots to find the problem.

    Does it have a sight glass?

    In any case I would be using thermocouples taped to the pipes and insulated from the outside air at this point. I would be measuring evaporator inlet, evaporator outlet and condenser outlet temperatures.
     
  19. rmllarue91

    rmllarue91 Senior Member

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    Thanks for the help I really appreciate the descussion I'm not the most technical with a/c yet. As far thermo couplers do you mean the type to a multi meter if you can post a link or a pic I'm interested in getting some. My customer is getting a local radiator shop owner that is a Reddot dealer out next Tuesday to shed some light. I will be there sucking up whatever I can from the guy. I will report back when I know more.
     
  20. Birken Vogt

    Birken Vogt Charter Member

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    This is what I use since I didn't buy a meter that already had the setting on it

    https://www.flukeonlinestore.com/products/temperature/80tk-thermocouple-module

    The trouble with measuring lines and hoses with a point and shoot is that the outside of the line will be affected by all the ambient air the engine fan is throwing around. But if you tape a thermocouple to the line in question and then insulate it with some foam rubber or even a wad of paper towel or a rag then the surface of the hose or line will quickly be the same as the fluid inside and then you can get a good idea what is going on. Good for thermostat diagnosis and air conditioning.