Page 1 of 3 123 LastLast
Results 1 to 13 of 27
  1. #1
    Join Date
    Dec 2007
    Posts
    37

    Best deforst cycle?

    Hi,

    Carrier 38SQ system - it has three defrost cycle choices (30, 50 or 90 minutes). Which is best? (Located in Montreal, Canada, if it makes a difference)

    Thanks.

  2. #2
    Join Date
    Dec 2006
    Location
    Middle Tennessee
    Posts
    11,347

    *

    Quote Originally Posted by KrisAMS View Post
    Hi,

    Carrier 38SQ system - it has three defrost cycle choices (30, 50 or 90 minutes). Which is best? (Located in Montreal, Canada, if it makes a difference)

    Thanks.

    in canada use 30!



    .

  3. #3
    Join Date
    Apr 2005
    Location
    NE PA
    Posts
    698
    You can't say what is best. A lot depends on the local weather environment. More humid areas will require shorter defrost cycles. Here in PA I always use 90 min and have had no problems. Shorter times will cause more frequent, and possibly unneeded defrosts, with higher costs. If you are in a area that will need a shorter time and you are set to 90, you may end up being iced up more often and use aux heat until it defrosts.

    Start with 90 and reduce if you tend to ice up too much.

    paul

  4. #4
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,613
    We find, especially with newer Carriers which have tight fin spacing, that 90 minutes is a problem. They spend much of the time frosted. Best bet is try 90 but probably will find that 50 might be better.

    There's a Carrier around the corner from me, unless it is dry & sunny, that sucker is probably gonna be frosted up. If real bad weather, it gets overwhelmed due to 90 minute defrost and never clears up.

  5. #5
    Join Date
    Feb 2006
    Location
    Tn.
    Posts
    1,344
    default should be 90 min. from factory. Dont change that if you dont have too.

  6. #6
    Join Date
    Apr 2005
    Location
    Kingston Ontario Canada
    Posts
    1,234
    Quote Originally Posted by KrisAMS View Post
    Hi,

    Carrier 38SQ system - it has three defrost cycle choices (30, 50 or 90 minutes). Which is best? (Located in Montreal, Canada, if it makes a difference)

    Thanks.
    I live in southeaster Ontario and have a Carrier 38YZA heatpump and use 50 mins defrost selection. I have never tried the 90 minute choice but I would think it would spend a lot of it's time frosted up, and I believe you loose efficiency when they start to frost. Like a couple of the other chaps stated it depends on the climate and especially how humid it is in your locale.

    thorton
    __________________
    I'm not going bald
    I'm getting more head

  7. #7
    Join Date
    Jun 2006
    Location
    Southeastern Connecticut
    Posts
    844
    Quote Originally Posted by thorton View Post
    I live in southeaster Ontario and have a Carrier 38YZA heatpump and use 50 mins defrost selection. I have never tried the 90 minute choice but I would think it would spend a lot of it's time frosted up, and I believe you loose efficiency when they start to frost. Like a couple of the other chaps stated it depends on the climate and especially how humid it is in your locale.

    thorton
    __________________
    I'm not going bald
    I'm getting more head
    You may lose some efficiency when they frost but but I bet you lose more when your switching to a/c mode every 50 minutes instead of 90. Areas that have higher humidity need to defrost more often. I always set defrost for 90 minutes in my area.

  8. #8
    Join Date
    Dec 2006
    Location
    Middle Tennessee
    Posts
    11,347

    *

    i always set them up for 30min even in middle tenn.

    no more cry baby customers, besides if the coil is not frozen it aint gonna try to defrost

    i know that will drive the light bill up a little bit, but gone are the whining not warm enough customers



    .

  9. #9
    Join Date
    Apr 2005
    Location
    Kingston Ontario Canada
    Posts
    1,234
    Quote Originally Posted by dngtig View Post
    You may lose some efficiency when they frost but but I bet you lose more when your switching to a/c mode every 50 minutes instead of 90. Areas that have higher humidity need to defrost more often. I always set defrost for 90 minutes in my area.
    Hi dngtig! So just to get this straight, are you suggesting that it is better to use 90 min defrost cycle, even though the condenser may be covered in frost for an extra 40 mins? If you are you may have a good point there! I never thought of it that way. I think I may set my timer to 90 mins and see what happens. I guess that if it's too humid in my area it will just stay frosted, but not ice up in 90 mins?
    I have always wished I could use the 90 defrost cycle to save wear and tear on the reversing valve, but was always afraid of the consequences of too much frost forming and hurting efficiency, and high pressure problems.

    thorton
    ________________________
    Without passion, all the skill in the world won’t lift you above craft.
    Without skill, all the passion in the world will leave you eager, but floundering.
    Combining the two is the essence of creative life.
    Last edited by thorton; 12-25-2007 at 10:54 AM. Reason: typing error

  10. #10
    Join Date
    Apr 2005
    Location
    NE PA
    Posts
    698
    Quote Originally Posted by Airmechanical View Post
    if the coil is not frozen it aint gonna try to defrost
    Actually where it is only mildly humid, the coil will be a few degrees above ambient. Here in PA, when we have a really cold spell, it is usually very dry air. The coil will get down to the teens or 20's, and the heat pump will run almost continuously to keep up. In these conditions the unit will tend to defrost every 30, 50 or 90 minutes, depending on the setting, even though there is little or no frost on the coils. True it may result in an occasional call from a customer, but it does save electric. Conversely if it does ice up, the coil will chill enough to trigger a defrost. The only loss might be some aux heat till it defrosts. As I had said it really depends on the local climate as far as what is the best setting.

    paul

  11. #11
    Join Date
    Dec 2006
    Location
    Middle Tennessee
    Posts
    11,347

    *

    Quote Originally Posted by thorton View Post
    I have always wished I could use the 90 defrost cycle to save wear and tear on the reversing valve, but was always afraid of the consequences of too much frost forming and hurting efficiency, and high pressure problems.
    i dont think wear and tear on the reversing valve is an issue

    also its not the high pressure, (the pressures are reduced while frosting occurs)

    but its the slugging that the compressor experiences when liquid refrigerant

    is sucked into the compressor during extended coil frosting that slowly kills compressor valves!



    .

  12. #12
    Join Date
    Apr 2005
    Location
    Kingston Ontario Canada
    Posts
    1,234

    Confused

    Quote Originally Posted by Airmechanical View Post
    i dont think wear and tear on the reversing valve is an issue

    also its not the high pressure, (the pressures are reduced while frosting occurs)

    but its the slugging that the compressor experiences when liquid refrigerant

    is sucked into the compressor during extended coil frosting that slowly kills compressor valves!



    .
    Yes, thanks, Airmechanical! I wasn't sure if it would, or could cause high or low pressure problems, I should have just used the generic word "pressure" problems when I didn't know for sure (poor choice of words on my part.) If what you state is true about " extended coil frosting kills compressor valves," isn't that the role of high and low pressure switches that my heat pump is equipped with, to shut down compressor before these extended coil frosting do waste the compressor valves? I'm glad you pointed out that more frequent defrosting (30-60-90 mins) is not an issue in reversing valve wear and tear. Now, I'm not sure if having my defrost timer on 50 mins is the right way to go. I believe it was you that suggested 30 min defrost cycle was the way to go in cold climates. I certainly have noticed that with my existing 50 defrost timer, the copeland schroll compressor does seem to do some labouring and vibrates quite a bit the last few minutes of a run cycle before a it goes into a defrost. Then it is much quieter. You really have me thinking now. Thanks so much for the heads up!

    thorton
    ______________________
    A mind once stretched by a new idea
    Never returns to its original dimensions
    Last edited by thorton; 12-25-2007 at 03:51 PM. Reason: typing error

  13. #13
    Join Date
    Jun 2005
    Posts
    14
    reversing valve solinoid no problem, also i hope carrier is using scroll compressor no valve problems. scrolls can pump some liquid and get a way with it.
    defrost timer is going to look at defrost thermostat for permission to go into deforst every 30, 50, or 90 min whatever you set it at. 50 min maybe a good place to start at.

Page 1 of 3 123 LastLast

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