Results 1 to 11 of 11
  1. #1
    Join Date
    Jan 2008
    Location
    Lehighton, Pa.
    Posts
    178

    Lennox XP-16 Demand Defrost ?

    I have the Lennox XP-16 which has demand defrost. Last night the o/d temp was around 26 deg. The system seemed to go into defrost every 34 minutes exactly. It only stayed in defrost mode about 3 minutes each time. Since it seemed like an abnormal amount of defrost cycles, I looked outside at my unit during one of the cycles. There was no frost on the coils and only a little dripping on the ground. I did notice that the cars and lawn had a coating of frost, so it was damp out.

    I this normal operation? I thought that with the demand system, the defrost cycle would be more sporadic as opposed to an exact timeframe between each and every cycle.

  2. #2
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,837
    I'm not intimate with your Lennox unit. Maybe a Lennox tech will respond with better info but many of the higher efficiency HPs have an artifical memory that also plays into the equation. That is, if it's been defrosting every nearly every 45-minutes and stayed in defrost for 10-minutes, it'll automatically shorten the defrost inerval and stay in defrost for a shorter cycle before terminating. So for example, if it continued to wait until it demanded a defrost at 45-minutes and stayed in defrost for 10-minutes, that's a total 55-minute cycle. But by shortening the defrost interval to 34-minutes and defrosting for just 3-minutes, the total defrost time per hour is reduced to 6-minutes for 68-minutes of operation for greater efficiency. This may be what's happening on your unit. When it senses that the defrost needs to be terminated in substantially less than the 3-minutes, it'll go back to a demand until it detects another trend. That may be correct or incorrect for you specific unit but that's the way many of the units we work on operate.
    If YOU want change, YOU have to first change.

    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

  3. #3
    Join Date
    Jan 2008
    Location
    Lehighton, Pa.
    Posts
    178
    Let me quote from the installation manual. Maybe this can help you with my question.

    " If the compressor runs longer than 34 minutes and the actual difference between the clear coil and frosted coil temperatures exceeds the maximum difference allowed by the control, a defrost cycle will be initiated".

    Does this mean that it checks the temp. variance between the two sensors (every) 34 minutes and if the difference shows the required spread, it will trigger the defrost?

    By the way, the defrost termination is dictated by a temperature that can be set on the defrost board.

  4. #4
    Join Date
    Mar 2007
    Location
    Toronto
    Posts
    43
    The unit will go into defrost every 34 min if there is no ice sensed on the coil. If ice is sensed on the coil it will immediately go into defrost. The way the defrost shuts off is by sensing the discharge temperature in the condenser. Usually set for 60 degrees f. After it senses this temperature it will go back into heating mode.

  5. #5
    Join Date
    Jan 2008
    Location
    Lehighton, Pa.
    Posts
    178
    [QUOTE=fd3687;2700402]The unit will go into defrost every 34 min if there is no ice sensed on the coil. If ice is sensed on the coil it will immediately go into defrost.

    What you're saying makes no sense. Why would it go into defrost if there is no ice?

  6. #6
    Join Date
    Jun 2006
    Location
    New Jersey
    Posts
    4,336
    It sounds like there is a problem, the board is not calibrating. You sure its every 34 minutes it's going into defrost? The unit calibrates after every defrost, it needs 20 minutes of stable temp to do so. If it doesn't it goes into defrost in 45 minutes. If it does calibrate, then it will only go into defrost when the clear coil and frosted coil temp goes beyond the prest temp on the board or after 6 hours of run time.

    Have the installing contractor come out a take a look.

  7. #7
    Join Date
    Jan 2008
    Location
    Lehighton, Pa.
    Posts
    178
    Quote Originally Posted by ascj View Post
    It sounds like there is a problem, the board is not calibrating. You sure its every 34 minutes it's going into defrost? The unit calibrates after every defrost, it needs 20 minutes of stable temp to do so. If it doesn't it goes into defrost in 45 minutes. If it does calibrate, then it will only go into defrost when the clear coil and frosted coil temp goes beyond the prest temp on the board or after 6 hours of run time.

    Have the installing contractor come out a take a look.
    It definitley goes into defrost at exactly every 34 minutes. Based on what I'm reading 34 minutes is how it operates when the heat is initially energized. It's weird because what I read is it should only revert back to 34 minute time/temp mode if the defrost is terminated by the 14 minute maximum time. Yet as previously stated, it's only in defrost for about 3 minutes.

    The dealer can't seem to figure it out. They already changed the sensors and defrost board based on Lennox's recommendation.


    Any Lennox experts out there?

  8. #8
    Join Date
    Jun 2006
    Location
    New Jersey
    Posts
    4,336
    Quote Originally Posted by jeepgrady View Post
    It definitley goes into defrost at exactly every 34 minutes. Based on what I'm reading 34 minutes is how it operates when the heat is initially energized. It's weird because what I read is it should only revert back to 34 minute time/temp mode if the defrost is terminated by the 14 minute maximum time. Yet as previously stated, it's only in defrost for about 3 minutes.

    The dealer can't seem to figure it out. They already changed the sensors and defrost board based on Lennox's recommendation.


    Any Lennox experts out there?
    Then if you are timing it and its going into defrost every 34 minutes then something is reseting the defrost control after every defrost. Something is not wired right or might have a short in the low voltage.

    I can't get to detailed. But has your service company been out when the outdoor temp in below 35 degrees to see why the defrost board in reseting.

  9. #9
    Join Date
    Jan 2008
    Location
    Lehighton, Pa.
    Posts
    178
    Unfortunately, I'm in SC and it doesn't get under 35 too often and when it does, the service guys are already tucked in for the evening.

    While I know that you cannot get too technical, all I'm looking for is info to pass on to the tech to enlighten him.

  10. #10
    Join Date
    Jun 2006
    Location
    New Jersey
    Posts
    4,336
    Quote Originally Posted by jeepgrady View Post
    Unfortunately, I'm in SC and it doesn't get under 35 too often and when it does, the service guys are already tucked in for the evening.

    While I know that you cannot get too technical, all I'm looking for is info to pass on to the tech to enlighten him.
    Well it's tough then, I'm sure the only time you are seeing this problem is below 35 degrees.

    It sounds like a low voltage problem reseting the defrost control, they should also being able to trigger it in "test" mode.

  11. #11
    Join Date
    Jan 2008
    Location
    Lehighton, Pa.
    Posts
    178
    I think you are right. I don't recall it happening unless it is that cold.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event