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  1. #1
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    Oct 2002
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    Carrier 38AKSO14

    Found one of the fans not running on this one today. Found the fan cycle switch not making, so I opened the door to let the pressure rise, and it did finally come on. Put the door back on and the head pressure droped to around 205. The sight glass was full. The suction pressure was 60 and the suction line temp was around 68. The outdoor temp was 90 and the indoor temp was 76 per state regulations. Both fans were running with the numbers I am posting.
    I hooked up and put in some R-22 to try to get the head pressure up and to get the line temp to around 90 degrees and the head to about 235. This is a TXV unit. It is a twin system, so the other unit is evidently toating the load. What bothers me here is that the suction line never got below 65 degrees the whole time I was charging it. The pressures seem to be dead on the chart numbers. I think that I know what may be wrong with this unit, but I would like to have your ideas to confirm my theory. I charged the other unit to pretty much the same numbers, but the line temp on it wound up to be around 45-50 degrees or so. Your ideas are appreciated here. Thanks

  2. #2
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    Jan 2008
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    Was your compressor running loaded or unloaded?

  3. #3
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    Oct 2002
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    Lexington, NC
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    I did not notice an unloader on the compressor. This compressor is smaller than the compressor on the twin unit. Being that neither of them seem to cycle, I would think that it would have been loaded. I must admit, I need to do some learning about unloaders. I see them a bunch, but I am not really familiar with what they do exactly. I do know that I usually see lower pressures when the unloader is engaged.

  4. #4
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    That should be a 6 cylinder and should have 1 unloader whether it be enectric or pressure. If electric and it is energized then it is unloaded. De-energized compressor is loaded. Unloaded pressure suction higher discharge lower loaded suction pressure lowers and discharge rises. Can also check amp draw to check.

  5. #5
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    Quote Originally Posted by thegoodlistener View Post
    That should be a 6 cylinder and should have 1 unloader whether it be enectric or pressure. If electric and it is energized then it is unloaded. De-energized compressor is loaded. Unloaded pressure suction higher discharge lower loaded suction pressure lowers and discharge rises. Can also check amp draw to check.
    I did not check the amp draw today, but I did look for the unloader. The part doesn't have a selonoid. It is basically a round piece at the bottom, goes into a larger round piece resembling the head of a TXV, and then goes back down to the smaller size of round at the top. The suction line was cool this morning, and the head was running around 190. This afternoon the line was back around 68 degrees.
    The twin unit has a larger compressor, but they both are the same model unit. It also has an electric selenoid. I am wondering if Carrier made a change on this model. I did not see anything about an electric selenoid on the schematic of my problem unit.
    While I am asking, what exactly powers up the selenoid to make it unload?

  6. #6
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    There should be a normally closed relay in the unit and when y2 makes it causes the relay to open and takes power off of the unloader.

  7. #7
    Join Date
    May 2008
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    Jax Fl.
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    Quote Originally Posted by nchvac View Post
    I did not check the amp draw today, but I did look for the unloader. The part doesn't have a selonoid. It is basically a round piece at the bottom, goes into a larger round piece resembling the head of a TXV, and then goes back down to the smaller size of round at the top. The suction line was cool this morning, and the head was running around 190. This afternoon the line was back around 68 degrees.
    The twin unit has a larger compressor, but they both are the same model unit. It also has an electric selenoid. I am wondering if Carrier made a change on this model. I did not see anything about an electric selenoid on the schematic of my problem unit.
    While I am asking, what exactly powers up the selenoid to make it unload?
    Hopefully this will be helpful; Carrier has two types of unloaders. The electric version has a small solenoid coil that energizes to unload and also enables the #2 condenser fan on some models.
    The second type is a suction pressure controlled unloader that has a giant nut that unscrews to lower the suction/loading up the compressor. There is a small cap nut perpendicular to the setpoint nut that encloses the differential adjusting screw. Be careful not to run in hard the large sepoint nut or you will flex the poppet diaphragm and ruin the unloader.

  8. #8
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    This must be the suction controled kind. I described it in an earlier post, but it comes out of the machine round, goes into a larger round part that rembles the head of a TXV(probably the diaphragm) and then goes into a smaller round piece. How do you know if the machine is running loaded or not with this type of unloader?
    I checked today, and the suction line is still running around 70 degrees. I just can't figure out why the pressures look dead on, the subcooling is dead on, and the suction line temp is so high. Any help is appreciated.

  9. #9
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    Quote Originally Posted by nchvac View Post
    This must be the suction controled kind. I described it in an earlier post, but it comes out of the machine round, goes into a larger round part that rembles the head of a TXV(probably the diaphragm) and then goes into a smaller round piece. How do you know if the machine is running loaded or not with this type of unloader?
    I checked today, and the suction line is still running around 70 degrees. I just can't figure out why the pressures look dead on, the subcooling is dead on, and the suction line temp is so high. Any help is appreciated.
    The way to see if it is runing loaded/unloaded is by measuring the compressor-only amp draw. It will be closer to RLA when loaded. 99% of the time the problem you are looking at is due to one of the two TXVs on the coil having a flat powerhead or having too much spring pressure [valve adjusted too high of a superheat]. You might also have a closed liquid line solenoid on the second stage TXV also.
    When you get the TXVs solved make sure your unloader setpoint is between 60-65 PSI and that the differential is >5 PSI to prevent hunting/wearing out the unloader. Only adjust the unloader setpoint nut by hand, do not use a wrench.

  10. #10
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    Jul 2008
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    Philly,PA
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    This unloader is operated on pressure only. the suction pressure will drop if compressor is running at full capacity.get some literature from your carrier distibutor and it will show you how to adjust cut in and cut out of unloader.

  11. #11
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    Quote Originally Posted by JRINJAX View Post
    The way to see if it is runing loaded/unloaded is by measuring the compressor-only amp draw. It will be closer to RLA when loaded. 99% of the time the problem you are looking at is due to one of the two TXVs on the coil having a flat powerhead or having too much spring pressure [valve adjusted too high of a superheat]. You might also have a closed liquid line solenoid on the second stage TXV also.
    When you get the TXVs solved make sure your unloader setpoint is between 60-65 PSI and that the differential is >5 PSI to prevent hunting/wearing out the unloader. Only adjust the unloader setpoint nut by hand, do not use a wrench.
    There is not liquid line selenoid, but if it was closed I would think that the suction pressure would go sky high in an effort to pump down the unit into the evap coil. Either way, the pressures should be off. I will try to adjust the TXV. I assume that when you say a flat power head, you are saying that the power head has gone bad? This is something that I wondered about, but I figured that the suction pressure would be really low because when a TXV goes bad, it closes down almost or all the way shut doesn't it? Thanks

  12. #12
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    Jul 2008
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    Philly,PA
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    I was a little confused in your statement. If there is a liquid line solenoid and it closes the suction pressure will drop and the refrigerant will all go into the condenser not the evap coil.Sounds like you have a metering device problem.

  13. #13
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    Quote Originally Posted by JRINJAX View Post
    The way to see if it is runing loaded/unloaded is by measuring the compressor-only amp draw. It will be closer to RLA when loaded. 99% of the time the problem you are looking at is due to one of the two TXVs on the coil having a flat powerhead or having too much spring pressure [valve adjusted too high of a superheat]. You might also have a closed liquid line solenoid on the second stage TXV also.
    When you get the TXVs solved make sure your unloader setpoint is between 60-65 PSI and that the differential is >5 PSI to prevent hunting/wearing out the unloader. Only adjust the unloader setpoint nut by hand, do not use a wrench.
    Don`t worry about the txv statement might be a little over your head right now but it will come in time.

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