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Thread: Carrier RTU

  1. #1
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    Carrier RTU

    Today I had to replce a compressor in a 4 TON carrier RTU. recovered 4.7 Lbs. of refrigerant from the system, just like the name plate says. After I installed the new compressor and filter dryer. I chared the thing with exactly what the name plate stated and what I pulled out 4.7 Lbs. Fired the thing up 50 Lbs suction pressure. Ok I waited for it to come up, nothing hung at 50 I started to see the evaporator ice up. Ok airflow, so I check the filters, coil, fan, and belt, all good. So I ran the unit again, and checked subcooling and superheat. Everything indicated it was low on charge. So I start adding refrigerant till I got my readings where I wanted them. 2 Lbs over before I got what I wanted. It ran fine on 7 Lbs of charge. I've never seen this before any ideas?

  2. #2
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    Sounds like metering devices

    I've had Carrier units that, after changing out compressor, they do the same thing as you described. Check the metering devices. You'll probably end up having to pull the header and clean/replace the orifices. Best of luck.


    Bill

  3. #3
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    Factory nameplate charge is the starting point.

    I can only judge by the information you posted, but I see no real indication of airflow besides 'all good'.

    The original compressor might have failed because your particular application required more charge.
    Perhaps you should have read the instructions before calling.

  4. #4
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    Quote Originally Posted by jrbenny View Post
    Factory nameplate charge is the starting point.

    I can only judge by the information you posted, but I see no real indication of airflow besides 'all good'.

    The original compressor might have failed because your particular application required more charge.

    shouldnt need an extra 2.3 pounds on a carrier roof top unit that calls for only 4.7 pounds total.

  5. #5
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    Quote Originally Posted by y7turbo View Post
    shouldnt need an extra 2.3 pounds on a carrier roof top unit that calls for only 4.7 pounds total.
    Exactly I've never had this problem before and I've changed out countless compressors, funny thing is the evaporator was freezing evenly as if it was low on charge. this is a 48TJE model and I have heard of problems with restrictions after compressor change outs however my head preasure was right on the money

  6. #6
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    Typically an evap doesn't frost up immediately because of low charge. What was your SH after putting in only 4.7lbs.? What was it after the additional 2lbs.? Don't see why the data plate would say 4.7 if it was not correct. If it was a split with additional lineset, then yeah.
    You changed the LLD? Frosting evenly across the coil seems like a restriction,(airflow)possibly.
    I like to take the filter panel off to ensure a good load across the evap coil.

    I had one yesterday that stumped me. York split with Aspen A/H. Call was for not cooloing properly. The stat said 78, set at 70. TD was 3. Go up on the roof. 30ft.lineset. Press. were 72lo 285hi, 24 SH, 66? SL, 100 LL, 30? SC, 98 amb, 0*TD across LLFD. No suction drier. Tried adding 1/2 lb r-22. Head shot up to 355, SC shot over 50*, suction went down a couple of lbs. SH went up 2 degrees. Now this ain't right. Tried removing 1lb. Now we are below where I started. Still ain't cooling right. Look at the A/H, Suction line sweating, not frosting, 58*SL 95*LL still only 2-3 TD.

    Finally it hits me, There has to be a restriction in the metering device. Press are good, even after adjusting the charge either way TD wouldn't budge. Will have to go back next week to repair after getting approval.
    Last edited by chaard; 07-19-2008 at 09:51 AM.
    Discipline your child so that other parents don't have to.

    We're awl pawthetic and kweepy and can't get giwrls. That's why we fight wobots.

  7. #7
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    Quote Originally Posted by Tiger93rsl View Post
    Today I had to replce a compressor in a 4 TON carrier RTU. recovered 4.7 Lbs. of refrigerant from the system, just like the name plate says. After I installed the new compressor and filter dryer. I chared the thing with exactly what the name plate stated and what I pulled out 4.7 Lbs. Fired the thing up 50 Lbs suction pressure. Ok I waited for it to come up, nothing hung at 50 I started to see the evaporator ice up. Ok airflow, so I check the filters, coil, fan, and belt, all good. So I ran the unit again, and checked subcooling and superheat. Everything indicated it was low on charge. So I start adding refrigerant till I got my readings where I wanted them. 2 Lbs over before I got what I wanted. It ran fine on 7 Lbs of charge. I've never seen this before any ideas?

    I have seen them take as much as a half hour to forty five minute to settle out...They also tend to run in the upper 50 lb's range, 50 lb's is to low...I vote restriction...now it's up to you to figure out where...

    Sometimes If possible I will run a torch or heat gun over the orifices while the unit is running, don't bake the effing things just heat them up...you may even hear it free up...or see it in a rapid rise on the suction side... or maybe not... In your case if this happens you are going to want to get the extra charge out of the system...I would change the filter/drier again.

    Does this count as my good deed for the day…I sure hope so…

    Good luck.

    .
    "Nothing else can poison our culture, corrupt our society or ruin the character of our people like unearned money or unearned opportunity." -- James R. Cook

    "Fooling around with alternating current is just a waste of time. Nobody will use it, ever." Thomas Edison, 1889.

  8. #8
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    Quote Originally Posted by Tiger93rsl View Post
    Exactly I've never had this problem before and I've changed out countless compressors, funny thing is the evaporator was freezing evenly as if it was low on charge. this is a 48TJE model and I have heard of problems with restrictions after compressor change outs however my head preasure was right on the money

    what were your superheat and subcooling numbers? if you pulll that 2.3 pounds out and check the subcooling right before the liquid line get to the orifice manifold and its high like 25+ and your superheat is nowhere near the chart. you can bank on the refrigerant getting backed up in those orifices.

    takes a 1-2 weeks to get the orifice manifold if they have to be made and not in stock. their easy to replace.I have done 4 this summer so far.
    Last edited by y7turbo; 07-19-2008 at 04:15 PM.

  9. #9
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    We have had similar problems with these rooftops. We had one mechanic remove the filter drier he installed and blew out liquid line with nitrogen. Unit ran good and was not freezing. Someone on this site said make sure u blow nitrogen through system while brazing. Sounds like a good idea considering how small those flow resrtictors are and how easily they can get clogged up. Oh and don't forget CARRIER ROOFTOP UNITS ARE JUNK!!!!!

  10. #10
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    Quote Originally Posted by rmac2 View Post
    Oh and don't forget CARRIER ROOFTOP UNITS ARE JUNK!!!!!


    Only eight post before you made a stupid comment, I did not check the other seven...


    I have worked on many brands over the last 35 years or so, so I can say for sure that you are wrong. I have seen great rtu's and crappy rtu's from all the manufacturers...more times then not it is the service tech that is the main problem. Over all my experience with Carrier has been excellent. You are posting on an open area, you should use some discretion. Other then that I have no more to say.

    .
    "Nothing else can poison our culture, corrupt our society or ruin the character of our people like unearned money or unearned opportunity." -- James R. Cook

    "Fooling around with alternating current is just a waste of time. Nobody will use it, ever." Thomas Edison, 1889.

  11. #11
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    I will agree with you, older carrier units were good but as you know alot of equipment has declined in craftmanship. But I have worked on alot of rooftop units and by far CARRIER UNITS have been the most trouble. Sorry if I insulted your excellent opinion of Carrier!!!

  12. #12
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    Quote Originally Posted by rmac2 View Post
    Trane ROOFTOP UNITS ARE JUNK!!!!!
    There I fixed it for ya!

    Carrier RTU's are the most fun to work on.
    Discipline your child so that other parents don't have to.

    We're awl pawthetic and kweepy and can't get giwrls. That's why we fight wobots.

  13. #13
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    Quote Originally Posted by chaard View Post
    There I fixed it for ya!

    Carrier RTU's are the most fun to work on.

    You are the bestest fixer upper there is...


    I like all rtu's...


    .
    "Nothing else can poison our culture, corrupt our society or ruin the character of our people like unearned money or unearned opportunity." -- James R. Cook

    "Fooling around with alternating current is just a waste of time. Nobody will use it, ever." Thomas Edison, 1889.

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