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Case 210C has A/C problem

Discussion in 'Excavators' started by Shimmy1, Jun 4, 2017.

  1. Junkyard

    Junkyard Senior Member

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    I thought I knew a little about A/C stuff. I don't know jack! Wow
     
  2. Birken Vogt

    Birken Vogt Charter Member

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    The way I think of refrigerant systems is the opposite of the usual way.

    Most people tend to think of the system with the compressor compressing gas, condensing it to liquid, and then it vaporizes somehow and provides cooling.

    I prefer to think of it like this: Think of the compressor pulling down the pressure inside the evaporator. The tail end of the high side is a reservoir of warm liquid to measure into the evaporator and when it hits the low pressure zone it gets cold fast.

    If you have spent a lot of time working with propane or similar liquid gases that come in a warm pressure tank it is more intuitive. When you let liquid out you have the potential to make your fingers very cold.

    In the case of this problem we need to know whether the condenser is full of liquid or empty.

    I agree with the above that most systems I work on that have a lost charge will have both high and low side pressures low. I don't quite know what could be causing the high side to run so high especially when it was not that hot out unless something is not letting refrigerant through.

    It would also help to know whether the clutch cycling device is pressure based or thermostatic on this model and where it is located.
     
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  3. Junkyard

    Junkyard Senior Member

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    Could the high pressure reading be a fubar'd gauge? I overcharged one last summer due to a faulty gauge.
     
  4. Shimmy1

    Shimmy1 Senior Member

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    Thanks for the replies, guys. I've kind of put together what everyone has been trying to say, and I'm fairly certain the tx valve is plugged/malfunctioning. Based on Birken's suggestion to check the temp on the condenser outlet, I'm more certain than ever that the valve/dryer is the culprit. The outlet is basically ambient temp, while the inlet (where the high side check port is) is hot to the touch. I did try and add a bit of juice today, smd promptly had to let it back out because high side pressure immediately went over 400 when the compressor kicked in. My gauges are new, been used about a dozen times.
     
  5. Shimmy1

    Shimmy1 Senior Member

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    Birken, I knew you were the one talking about using a thermometer to measure cooling on an A/C system, but couldn't find your previous posts. After I read one of your posts earlier, I checked the temp of the condenser outlet. It is basically ambient temp, not warm at all while the inlet is hot. If you feel the low pressure side, the line going back to the compressor, it's cool (but not cold), and you can feel the temperature changes as the compressor cycles. Cooler while running, warmer when kicked out. Based on Junkyard's experiences with plugged tx valves, I'm going to change the expansion valve and the dryer. The dryer is cheap, and easy to get to. BTW, the current dryer has a sight glass, and it is clear. Too clear. In all previous systems I've worked on, I've always seen at least some bubbles in the glass. This one stays clear all the time.
     
  6. Birken Vogt

    Birken Vogt Charter Member

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    Rig it up so you can start and stop the compressor with your eye on the sight glass and then watch it like a hawk while starting it from a good overnight. Should usually see some foam through there before it goes solid liquid. Then if you stop it you should see the liquid go back to foam and then vapor after some time passes. That is unless the high side is so far shut down that it will not drain the liquid in a reasonable time. Just another piece in the puzzle.

    If the system has dye in it the sight glass is much easier to tell, it will be green when full and clear when empty. Dump some dye when you are in there, good to have.
     
  7. Shimmy1

    Shimmy1 Senior Member

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    One more thing I forgot to mention earlier. I ran the system about an hour today, then shut it off. Dug for about two hours, loaded the hoe on the trailer, and ran down the road 20 miles at 60 mph. When I got to the yard, I hooked up the gauges before starting it, and the high side was at 140 psi, low side was about 115. Outside air temp was around 80°F.
     
  8. Birken Vogt

    Birken Vogt Charter Member

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    Interesting that they were not the same. But I have seen some TXVs that do not open except when there is real pressure being generated by the compressor.

    The pressures you see at rest like that are related only to the temperature of the liquid in that part of the system. Be it an ounce or a pound of liquid the pressure will be the same at any given temperature.

    140 psi = 107° probably the hot radiator nearby

    115 psi = 96° probably some leftover heat source nearby
     
  9. 007

    007 Well-Known Member

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    Hi guys sorry i missed the latest.
    Sounds like you are honing in on the prob.
    A lot of tx valves will not alow the system to equalize fully so is not a problem to see different pressures.
    At this point you could do some basic tests still.
    Chances are the receiver dryer will be ok prob tx valve problem.
    Assuming you have not over charged it to a point you will damage some thing you can check a few things at the tx valve.
    you can unscrew the capillary bulb off the leaving pipe of the evap and warm it and cool it and see if it is controlling the flow of liquid as it should.
    Some times we used to be lazy and just spray some coolant on the head of the tx if the bulb was hard to get to.
    If you see no changes on your gauges it would be high probability as the root cause.
    Cheers
     
  10. Birken Vogt

    Birken Vogt Charter Member

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    Something I thought about while driving around. One reason the high side goes high when first compressing is that the compressor is (probably) a fixed displacement unit. Meaning the more pressure you give it on the inlet side the more refrigerant it is pumping per stroke. Then as the low side pulls down, the compressor is more "starved" for refrigerant and there is less being moved from low to high for a given RPM and the high side pressure begins to drop. There are a lot of variables in this concept but that is the general idea.

    I hope to learn how this actual project turns out when the OP gets it fixed.
     
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  11. Shimmy1

    Shimmy1 Senior Member

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    I will most definitely post when I get it sorted out. I have decided to dig into the evaporator housing and make sure the coil doesn't have any sort of restriction on part of it. I have a new expansion valve and dryer, so if the evap and ductwork are clean, there really isn't much else to consider.
     
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  12. CatKC

    CatKC Well-Known Member

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    I agree with the above that most systems I work on that have a lost charge will have both high and low side pressures low. I don't quite know what could be causing the high side to run so high especially when it was not that hot out unless something is not letting refrigerant through.

    Perhaps this may help-
    The older terms are VACUUM (what a pump draws) and PRESSURE (what pump puts out) but I will relate this to LOW and HIGH.
    When an AC unit is -very low- on Freon both HIGH and LOW readings may both be lower than normal.
    However when an AC unit is -somewhat low- the expansion valve aka TEV/TXV/TX VALVE (or whatever you choose to call it) shuts off most of the flow of Freon, creating a -HIGH- high pressure reading. When an AC unit is -slightly low- on Freon the LOW side pressure (vacuum) gets low enough to the point to where the Freon -evaporates/cools- too quickly. When this happens the evaporator gets TOO COLD as the Freon is evaporating/cooling TOO QUICKLY.
    There is a small -tube- in the expansion valve that senses the temperature, which relates to pressure, of the evaporator. If the evaporator gets TOO COLD, the expansion valve RESTRICTS the flow of Freon, which results in a -HIGH- high pressure reading, to prevent FREEZING . This is the purpose of the valve, to PREVENT FROSTING/FREEZING/ICING of the outlet/evaporator. The evaporator must maintain a temperature above freezing or it will ice over and stop airflow.

    Whatever HIGH/LOW gauge pressure readings are considered normal will be slightly different and related to boiling points of different Freon's: F12= -21degF, F22= -41degF, F134A= -15degF at atmosphere, not under pressure.

    Refrigeration/AC is not complicated if one doesn't over think it.
     
    Last edited: Jun 17, 2017
  13. Birken Vogt

    Birken Vogt Charter Member

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    With all due respect, the TXV will happily freeze an evaporator into a solid block of ice. Its purpose is to control superheat, not temperature.

    For those who haven't heard this before, superheat is the number of degrees above the boiling point that the outlet gas coming out of the evaporator is at.

    So you feed liquid into an evaporator which is running at 26 psi, the liquid immediately begins to boil and drops to 30°. It continues to boil on its journey through (getting all the air cold) until all the liquid is used up and what is left is just gas/vapor. The last few turns of the coils are adding the superheat to the gas so no liquid reaches the compressor. This is where the TXV will measure it, just as it is leaving the evap. Let's say it is 10° superheat, it will be 40° leaving the evap. The TXV does this by comparing actual evaporator pressure to the pressure of a little bulb full of refrigerant that sensing the outlet gas and a spring to add a little force to the valve, otherwise superheat would be zero.

    Now let's say the cab got down to temperature so the operator turned the blower to low. Now there is much less air warming up the liquid that is flowing through so liquid is getting closer to the outlet. Superheat is getting less so the TXV closes down. Superheat goes back up to the setpoint, but what happened to the pressure inside the evaporator/suction?

    It dropped way down because there is less refrigerant flow into it. Now let's say the evaporator is running at 18 psi. This means the refrigerant coming in will be boiling at 19° which will quickly turn the whole mess into a block of ice.

    So there is another temperature sensing element that either senses the actual (absolute) temperature of the evaporator, or the pressure inside, (sometimes a variable compressor). It will stop the compressor pulling vacuum on the evaporator in order to allow the temperature to rise above freezing, then start the system again.
     
  14. CatKC

    CatKC Well-Known Member

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  15. Bc18

    Bc18 New Member

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    Sounds like your txv is bad.