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  1. #1
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    Question Questions on first job.

    Hello, new to the game here, few questions to make sure I'm on the right track. Some info for context:

    System is an old R22 hodgepodge. Story is, this thing was acquired on the cheap as used surplus when a nearby shopping center was rebuilt back in the 70s-80s. No idea who put it together or exactly when, and, given that this is a church where the administration has been completely replaced (retired/moved, mostly) multiple times since then, I'm never going to find out. Almost every kind of identifying mark is faded to the point of being unreadable. Anything regarding its original design specs I've had to suss out myself, and may or may not be accurate.

    The system had been seeing degrading performance for some time, but, as it is undersized in the first place, this wasn't really noticed until it got to the point of complete uselessness. Eventually was determined, by the company that does the regular A/C service, to be a low charge. Quote comes back for several thousand dollars to find/repair the leak, I offer to jump through the necessary hoops to be able to fix it, if the office agrees to pick up the tab for all the necessary equipment I didn't already have. Track the problem down to a leaking gasket on the compressor, easy enough fix.

    Now, I'm at the point that it should be ready for use, but it's showing a few problems not (directly) related to the leak.

    1.) There are two TXVs feeding the evaporator. I'm not sure WHY, because it's not like it's a split evaporator or anything, it's just a single evaporator with two inlets/outlets. One of the TXVs is operating normally, maintaining about 3F of superheat. Checking the other, however, shows that it's producing about 35F of superheat. Playing with the adjustment screw does nothing at all. Would I be correct in assuming that it's either failed or clogged? As an aside, why would there be two TXVs, both split off from the same (only) liquid line, feeding a single evaporator like this?

    2.) When I had the compressor open, I noticed the oil was an amber color. No odd smell, nor was it completely opaque, but definitely not like the crystal clear mineral oil I got to soak the gasket in. Worth doing an oil change, maybe?

    3.) I get no pressure at all out of the high-side service port. As in, depressing the valve core releases no gas. I had thought the valve core had maybe been clogged somehow, but nope. Replacing the core didn't help. Turns out, I can completely remove the core and nothing comes out. What the heck? I would think I had the wrong port somehow, but, no, aside from one connection that feeds a pressure monitor, it is the only port on the high side. This seems very weird that I get nothing out of it, and I can't for the life of me figure out why. The piece it's attached to can't possibly have any kind of valving in it, it's just a casting that turns the outlet of the compressor 90 and provides a hole for both a service port and much larger 1" fitting that's capped off. It's got a sizable accumulator and sight glasses before the TXVs, so I was at least able to fill it to a "that's about right" level of charge, but I can't very well determine subcooling or head pressure without a working port on the high side. The obvious solution is to just put another service valve in, especially since I expect to have to empty the system to replace that TXV, anyway. But if anyone has any idea why what should be a hole going straight into the high side plumbing doesn't have any pressure in it, I'm intensely curious.

    4.) Discharge temperature is high, in the neighborhood of 190F. I believe this is related to the bad TXV starving the compressor of some refrigerant.


    Any help/advice is appreciated.

  2. #2
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    If the evap has dual inlet and outlet and you are getting two different superheat readings that is a intertwined coil which requires two txvs. The casting you are taking about is it a service valve? Which may explain why you have no pressure on the port.

  3. #3
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    What model compressor is it?

  4. #4
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    Quote Originally Posted by Skrub View Post
    ...I get no pressure at all out of the high-side service port. As in, depressing the valve core releases no gas. I had thought the valve core had maybe been clogged somehow, but nope. Replacing the core didn't help. Turns out, I can completely remove the core and nothing comes out. What the heck? I would think I had the wrong port somehow, but, no, aside from one connection that feeds a pressure monitor, it is the only port on the high side. This seems very weird that I get nothing out of it, and I can't for the life of me figure out why. The piece it's attached to can't possibly have any kind of valving in it, it's just a casting that turns the outlet of the compressor 90 and provides a hole for both a service port and much larger 1" fitting that's capped off.
    Does this "casting" look something like this?


  5. #5
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    Thread Starter
    Quote Originally Posted by hvac69 View Post
    If the evap has dual inlet and outlet and you are getting two different superheat readings that is a intertwined coil which requires two txvs.
    I've already had a look at the coil when searching for the leak, but some Googling does clear things up a little. It's not an intertwined coil, but a face split. As far as I can tell, though, there's no actual staging going on. May just be a relic of it being surplus?

    Quote Originally Posted by hvac69 View Post
    The casting you are taking about is it a service valve? Which may explain why you have no pressure on the port.
    It does, in fact, look like icemeister posted.

    ...that cap is covering a valve stem that opens the port, isn't it?

    Quote Originally Posted by remanworld View Post
    What model compressor is it?
    I don't know for sure, I can't find any name plate, model number, or serial number on it. I know it's one of the Carlyle 06 compressors. Based on appearance and feature locations, it appears to be one of the 06E models.

  6. #6
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    People can be seriously injured or killed working with HVAC equipment if those people do not have a fundamental understanding of the equipment and are not extremely careful .

  7. #7
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    Under that 1 cap you may find your answer


    Sent from my iPhone using Tapatalk

  8. #8
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    Skrub, tell us a little about yourself and your HVAC background. Do you have an EPA license?

    You have to understand this is an open forum....anyone can walk in and ask questions. Advice given by people here could end up getting someone seriously injured. If you dont have any experience Im this field, you could inadvertently seriously damage the equipment youre working on....especially a reciprocating compressor.

    One thing that about your post that makes me feel this way is that are saying 3* of superheat is normal.

    While your intentions of fixing the equipment to save money is a good thought, many times there is a higher cost after the fact

  9. #9
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    Thread Starter
    Quote Originally Posted by remanworld View Post
    People can be seriously injured or killed working with HVAC equipment if those people do not have a fundamental understanding of the equipment and are not extremely careful .
    Quote Originally Posted by 71CHOPS View Post
    Skrub, tell us a little about yourself and your HVAC background. Do you have an EPA license?
    I should clarify that I'm not a random member of the congregation. I'm on the payroll as the maintenance guy ("sexton" is my official title). I already take care of the odd problems that crop up with the various HVAC systems around the premises, just not ones that require a set of gauges. Not until now, anyway. I got a universal 608 cert since I'd like to keep this kosher, so to speak, and I've never been one to say "no" to adding to my skill set. I'm well aware of the potential hazards, given the nature of the rest of my job. The only new one here is frostbite. Additionally, this is not a high-priority project. This system is only used one day a week, and usually not at all in the winter months. I'm free to proceed as cautiously as necessary. Case in point: I had suspected as much regarding the cap on the service valves before asking, but wanted to make damn sure before I cracked it loose.

    Quote Originally Posted by 71CHOPS View Post
    One thing that about your post that makes me feel this way is that are saying 3* of superheat is normal.
    I did think that was cutting it a little close, but this is also right after the evaporator. There's a good run of piping afterward, some of which runs underground, that brings the total SH to around 8F, if I remember my measurements correctly. I'm under the impression that this is within the expected range. Is it not?


    Anyway, if I haven't ruined anything already, I don't think I'm going to. Finally got a chance to have another look earlier today, but I'm kind of at a loss on this one. I took the problem TXV apart. Spotless, no gunk inside. Power head didn't feel empty (I couldn't depress the diaphragm by hand), but I swapped it with a new one since I didn't really have anything else I could try. That half of the evaporator STILL comes up with a crazy superheat, with no response to adjustment of the TXV.

    Any ideas? I can see through the sightglass that the TXV is not being starved of refrigerant, yet the TXV itself doesn't show any obvious physical problems. The only thing I can think of is that the distributor is clogged, but what are the odds of that clogging before the TXV does?

  10. #10
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    Ok, thanks for the info. Everyone starts from somewhere.

    That is a basic service valve. Back seat (counterclockwise) opens the compressor to the line, and closes the access port. Crack the valve (clockwise one turn) and your access port is open for service. Front seat the valve (clockwise 100%) isolates the compressor to the line.

    All compressor manufacturers have different specs. On all recip. Compressors, I go by 20* SH 18 from the compressor body. Watch design return gas temperature. Usually around 65* is max safety.

    If you have a liquid receiver (after condenser, before TXVs). You will have to calculate your system total refrigerant charge. Measure all your piping. Measure all the tubing In the condenser (including return bends), measure the liquid line, then use the capacity mutipliers for the piping sizes to calculate liquid volume. Calculate receiver capacity at 80% full. That will get you close to full operating charge. Google search the DuPont refrigerant piping hand book.

    Replace the expansion valve.

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