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Thread: Carrier rooftop charging issues

  1. #1
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    Carrier rooftop charging issues

    Hey guys, I’m having an issue with a old carrier rooftop unit with no TXV and a superheat that won’t seem to change when I add refrigerant from about 3° or 4° roughly.

    The model number on the rooftop unit is 48TME004–A–301

    With the system running I had an indoor wet bulb ranging from 60 to 62° and an outdoor dry bulb ranging from 80° to 83° so my target superheat should’ve been somewhere between 8° to 12°.

    My super heat was at about 3/4 degrees with 55psi on my low side and a 18 degrees sub cooling with a 210psi high side. I took out about a half a pound of refrigerant and the system froze up and went off on low pressure and I added 2lbs more just to see what would happen and my sub cooling went up like it should have but my super heat stayed the same around 3/4 degrees...any thoughts on why it wouldn’t change? Compressor? blockage?

  2. #2
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    Sounds like you're not transferring any heat at the evaporator.

    Dirty coil
    Low airflow
    Supply or return registers closed or blocked

  3. #3
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    Thread Starter
    Quote Originally Posted by 71CHOPS View Post
    Sounds like you're not transferring any heat at the evaporator.

    Dirty coil
    Low airflow
    Supply or return registers closed or blocked
    We cleaned both coils during the PM and changed the filters, But they had originally called us out there because the system was not cooling at all and we found that it had a broken fan belt a dead compressor capacitor and they almost failed fan capacitor so we replace the belt and both capacitors and did a PM on the system. Do you think that possibly the fan motor is also failing?


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  4. #4
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    Quote Originally Posted by HyperFusionHVAC View Post
    We cleaned both coils during the PM and changed the filters, But they had originally called us out there because the system was not cooling at all and we found that it had a broken fan belt a dead compressor capacitor and they almost failed fan capacitor so we replace the belt and both capacitors and did a PM on the system. Do you think that possibly the fan motor is also failing?


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    Many the blower is running backwards?

    Sent from the Okie state usin Tapatalk

  5. #5
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    blower wheel clean ....

  6. #6
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    Clean everything is good but for sure doesn't guarantee enough cfm.
    Find a way to measure it if possible.

    Sent from my SM-G950U using Tapatalk

  7. #7
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    Read the external static, evap DT.

    With 3-4 *f ssh, 55 psig you are not transferring heat per CHOPS.
    1. air flow
    2. dirty coil
    3. excess oil or ref side contamination (less common)

  8. #8
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    Way back when, I worked for a company that had several top notch techs, they never bled off their gauges, over time, the systems with small leaks would get non-condensables in the system and cause high head pressure with low suction, I literally would dump the charge(which is how we did it back in the olden days) then pull just a really fast vacuum and recharge to name plate data and the unit would start working again.
    "Orange Man RAD!"

  9. #9
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    This unit might have a header on the inlet of the evap coil from the liquid line. on the outlet of the header are brazed in fixed orifices which may be plugged. To check shut blower fan off and you can see is some are plugged by seeing frost on the inlet of the coil.
    If so good luck what a pain in the butt to change

  10. #10
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    Thread Starter
    Thanks for all the input here really appreciate it! Gonna try these things when I go back tomorrow

  11. #11
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    Quote Originally Posted by HyperFusionHVAC View Post
    Thanks for all the input here really appreciate it! Gonna try these things when I go back tomorrow
    If I get a call on a unit I have never seen before and I have wacky things happening, it is very common for me to recover the charge and weigh in a new charge as per the nameplate. The problems either go away or if there is truly a problem then it is easy to diagnose.
    I do a triple evac with nitro to remove non condensables.

  12. Likes DavidDeBord liked this post.
  13. #12
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    Quote Originally Posted by fac 213 View Post
    This unit might have a header on the inlet of the evap coil from the liquid line. on the outlet of the header are brazed in fixed orifices which may be plugged. To check shut blower fan off and you can see is some are plugged by seeing frost on the inlet of the coil.
    If so good luck what a pain in the butt to change
    plugged or leaking by?
    "Orange Man RAD!"

  14. #13
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    Quote Originally Posted by fac 213 View Post
    This unit might have a header on the inlet of the evap coil from the liquid line. on the outlet of the header are brazed in fixed orifices which may be plugged. To check shut blower fan off and you can see is some are plugged by seeing frost on the inlet of the coil.
    If so good luck what a pain in the butt to change
    If the orifices were restricted, the superheat would be high. Sounds like he has an airflow problem.

  15. #14
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    Check your temp probe (clamp or strap) it might be malfunctioning..It happens to me sometimes..
    I came across a 410a Trane RTU yesterday, 2 comps..Both metering manifolds at the evap. 1st stage was running fine till the 2nd stage kicked in, the 1st stage head pressure tripped, leaving 2nd stage only. 1st stage Green Comp much larger than the 2nd. Condenser needed a deep cleaning. Both stayed running afterwards. High superheat on the 1st stage..the crankcase heater was also no good..

    Now 1st stage was found with a lower suction and higher head..4-6degrees across the filter dryer and a The head Pressure not steady..+/-14psi..

    The compressor looks newer. I’m thinking too much oil From the other comp and possibly restriction. Waiting on the customer to approve recovery and replace Refrigerant / filter dryer / crankcase heater, blow out excess oil first..I go after the simple things first.

  16. #15
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    Rip out those crappy accutools and put in a TEV.Done many like that.It is a lot of work,But end result is good.There is a company in St.Louis that will make the feeds and distributors for you.(KeepFlo-800-233-1477) Tell them the type of freon, how many feeds and the tonnage.You need to add your own TEV .They will make the distributor with the feeds .Cut out the Accutrols ,Install feeds and TEV.I have done about 10 of these.A lot of work,But works great.Accutrols SUCK!!!!Especially when they plug up.

  17. #16
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    Air Flow
    Air Flow
    Air Flow

    Has TESP been tested?
    Evap motor amperage?

    Start looking for Fire Dampers, balancing dampers.

  18. Likes slctech liked this post.
  19. #17
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    Silly but is the IDF rotation correct..

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  21. #18
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    Thread Starter
    Quote Originally Posted by CHEYENNE2020 View Post
    Silly but is the IDF rotation correct..
    Yeah I checked that as well


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