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  1. #1
    Join Date
    Jul 2009
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    Northeast, Md.
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    Lennox 3ton Rooftop question.

    Lennox RTU
    M#LCH036H4EN Y
    S#5611H05061

    Copland Scroll 2 Stage
    M#ZPS30k4E-TF5-130
    S#11AG38D4N
    410A

    Unit is new and was just set a few months ago. Checked Prodigy control and find 2 Low pressure switch faults, and the third had locked it out. Reset system, and checked operation. System runs perfectly in 1st stage cooling. Pressures are great, Comp, fan and blower amps all within range and at proper speed. Everything is running according to design.

    2nd Stage Cooling kicks in. Blower and fan ramp up, amp draws are still doing great, and Suction just drops off the radar. Discharge Pressure remains constant and acts normal. Suction drops to 70psi.

    This is a single circuit system. Every component is used in 1st stage as 2nd stage. Only component that changes is the compressor. I am thinking the bypass ports are not closing and the compressor remains at 67% capacity. With the increased blower speed suction is falling off. I have never seen this before, so any input you guys have is appreciated.

    OAT 78'
    SAT 66
    RAT 78'

    1st stage
    Pressures 125-325
    Comp 4.7A
    Fan .9A
    Blower .76A
    Superheat 18'
    Subcooling 12'

    2nd Stage
    Pressures 70-325
    Comp 6.42A
    Fan 1.1A
    Blower 1.8
    Superheat 54'
    Subcooling 13'

    One thing i did not do was remove charge, and recharge to factory specs. I recommended that we rule that out before we condemn anything. I see no signs of oil anywhere, and I checked pressures according to unit chart and everything is up too par. I truly don't believe this is a charge issue.

    http://www.youtube.com/watch?v=uPhthHuZsQk

  2. #2
    Join Date
    Nov 2006
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    Southeastern Pa
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    17,907
    Are you sure this is a digital scroll?

    I haven't seen these yet in the small RTUs.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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  3. #3
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    Jul 2009
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    Quote Originally Posted by timebuilder View Post
    Are you sure this is a digital scroll?

    I haven't seen these yet in the small RTUs.

    Not a digital. Its the new Ultratech series. I provided a link at the bottom of the first post of how it works.


    http://www.emersonclimate.com/en-US/...ng_system.aspx

    https://www.google.com/url?q=http://...7TKUYGm6YQBNvA

  4. #4
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    Nov 2006
    Location
    Southeastern Pa
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    Well, it's a good thing it's locking out with superheat that high.

    With the variable speed compressor, are they using an EEV?
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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  5. #5
    Join Date
    Mar 2011
    Location
    East Coast FL
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    Your compressor current is increasing on high capacity, so it would seem the load / unload function is working.

    This is an ECM direct drive blower motor?

    Have you verified all of the correct settings in the Prodigy controller?

    The temp conditions posted look pretty mild..

    Your suction pressure drops off and the SH goes way up on high stage..

    It appears the valve is not feeding enough refrigerant for full capacity.

    Maybe pop a new power element on there and see what happens.

    Or a small shot of refrigerant?

  6. #6
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    The Copeland ultratech is just a solenoid activated load / unload scroll that provides a thirty something percent capacity drop.

    That unit should have a non-adjustable Sporlan with a removable power element.

  7. #7
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    Quote Originally Posted by AiResearch View Post
    The Copeland ultratech is just a solenoid activated load / unload scroll that provides a thirty something percent capacity drop.

    That unit should have a non-adjustable Sporlan with a removable power element.

    That's what I thought, too, but the info links he posted says "variable speed," not a "scroll lifter" like the digital scroll. Of course, the link info may not apply to that unit...
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    2 Tim 3:16-17

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  8. #8
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    Quote Originally Posted by AiResearch View Post
    Your compressor current is increasing on high capacity, so it would seem the load / unload function is working.

    This is an ECM direct drive blower motor?

    Have you verified all of the correct settings in the Prodigy controller?

    The temp conditions posted look pretty mild..

    Your suction pressure drops off and the SH goes way up on high stage..

    It appears the valve is not feeding enough refrigerant for full capacity.

    Maybe pop a new power element on there and see what happens.

    Or a small shot of refrigerant?

    Yes direct drive.
    Yes, all setting verified in controller.
    Yes, SH/SC normal on first stage. SH high, and SC normal on 2nd stage.
    Whats this power element you speak of? Please explain?
    Yes, I am going to weigh in a charge next time i am there. I would love if that worked, but just don't think that is it.

  9. #9
    whats the duct work look like

  10. #10
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    Quote Originally Posted by limmy09 View Post
    whats the duct work look like
    Very simple. Drops straight into a room, and return pulls from the room. No duct issues at all.

    No EEV, but just a normal TXV which i have diagnosed as operating properly. Again, this is a single circuit with the new ultratech Technology. First i have ever seen, but all i can come up with as a possible cause. I have checked this thing inside and out! Including all sensors on prodigy controller. SAT sensor seems to be a little out of wack to my readings, but that is the least of my problems at the moment. I have not totally ruled out a charge issue yet. I didn't have the equipment on site to remove charge, and recharge to factory specs. I did put unit into high mode, and check subcooling, and chart for units discharge pressure and all corresponded to what i was seeing. Guys this one is just off the wall for me. I won't sleep till i get to go back and figure this one out! LOL

  11. #11
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    Mar 2011
    Location
    East Coast FL
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    Quote Originally Posted by budman21901 View Post
    Very simple. Drops straight into a room, and return pulls from the room. No duct issues at all.

    No EEV, but just a normal TXV which i have diagnosed as operating properly. Again, this is a single circuit with the new ultratech Technology. First i have ever seen, but all i can come up with as a possible cause. I have checked this thing inside and out! Including all sensors on prodigy controller. SAT sensor seems to be a little out of wack to my readings, but that is the least of my problems at the moment. I have not totally ruled out a charge issue yet. I didn't have the equipment on site to remove charge, and recharge to factory specs. I did put unit into high mode, and check subcooling, and chart for units discharge pressure and all corresponded to what i was seeing. Guys this one is just off the wall for me. I won't sleep till i get to go back and figure this one out! LOL
    Just wondering, are you sure the expansion valve is okay?

    A new power element sometimes works wonders.

    Perhaps the sensing bulb was overheated, or maybe lost a portion of its charge.


  12. #12
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    Quote Originally Posted by AiResearch View Post
    Just wondering, are you sure the expansion valve is okay?

    A new power element sometimes works wonders.

    Perhaps the sensing bulb was overheated, or maybe lost a portion of its charge.


    Its a TXV with a sensing bulb. Please help me understand this if it applies Its not a EEV if that is what you mean.

  13. #13
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    I am attaching a PDF of the actual unit specifications. Thanks everyone for the replies.

    http://home.comcast.net/~budman21901/lennox.pdf

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