Results 1 to 9 of 9

Hybrid View

  1. #1
    Join Date
    Jan 2010
    Location
    Toronto,Ontario Canada
    Posts
    355

    defrost cycle electric defrost

    I was at a call this morning for a walk-in freezer. and i discovered the evap coil was iced up. its a new customer i already checked if the drain heater was working, it was. checked if the drains were plugged it was checked if the heaters on the coils were working in defrost, it was. i already made sure it couldnt be anything else but the length of the time in defrost.

    when i got there it was set for 4 times a day 6am noon 6pm and midnight. and it was set for 28 mins defrost it was an electric defrost.

    as a inspiring tech i thought about the coil being frozen, i considered the length was too short and i raised it to 40 mins long.

    my question is is 40 mins ok for a 2 fan evap system
    could i put the length a little bit longer just incase? i dont really remember about this part in school but if the length is too long will it jump into the cooling mode if the coils already gets the ice off and now its just making the evap too hot?

    wat is the normal length it should be in for?
    appreciate the help well in advance

  2. #2
    Join Date
    May 2004
    Location
    SE Pennsylvania
    Posts
    928
    Yes there should be a defrost termination thermostat. I have had jobs where the defrost timer would stop when it hit a pin and couldn't advance to initiate defrost. Check the condition of the evap, air flow across evap and check superheat, possible causes of excessive ice forming.

  3. #3
    Join Date
    Mar 2012
    Location
    Miami Florida
    Posts
    16
    40 minutes is to long unless you are 100% sure that the defrost termination works but even if it works 40 minutes is not correct. You will start to get ice building up all over the case because that is to much time off. You should not need more than 30 minutes 3 times a day for a walk-in freezer with electric defrost. You need to make sure that the heating elements are working. Also dont confuse frost that build up on the evap with ice. Lastly I would suggest that you check the door switch to make sure that the evap fans stop when the doors open and check if you have a drip timer on that defrost setup. It is the small things that could cause problems.

  4. #4
    Quote Originally Posted by akelesis View Post
    I was at a call this morning for a walk-in freezer. and i discovered the evap coil was iced up. its a new customer i already checked if the drain heater was working, it was. checked if the drains were plugged it was checked if the heaters on the coils were working in defrost, it was. i already made sure it couldnt be anything else but the length of the time in defrost.

    when i got there it was set for 4 times a day 6am noon 6pm and midnight. and it was set for 28 mins defrost it was an electric defrost.

    as a inspiring tech i thought about the coil being frozen, i considered the length was too short and i raised it to 40 mins long.

    my question is is 40 mins ok for a 2 fan evap system
    could i put the length a little bit longer just incase? i dont really remember about this part in school but if the length is too long will it jump into the cooling mode if the coils already gets the ice off and now its just making the evap too hot?

    wat is the normal length it should be in for?
    appreciate the help well in advance
    Many potentials. Refrigeration cycle FULLY stopped? Fans dropping out? Termination (if equipped) not prematurely ending defrost.

  5. #5
    Join Date
    Nov 2011
    Location
    British Columbia
    Posts
    48
    Humid weather in Toronto? The higher the humidity - the more frost there'll be. Need to set the defrost timer to whatever works. Should only have frost forming, not ice remaining. If that's the case then frost from the previous cyle didn't completely melt before restarting the cooling again.

    Your're on the right track.

  6. #6
    Join Date
    Jan 2010
    Location
    Toronto,Ontario Canada
    Posts
    355
    I meant defrost heaters not drain heaters! opps my fault
    and o ya i forgot to mention evaporator was dirty because i remember finding a lot of dirt build up on the evaporator so i went thru with my coil brush (matching the number of fins) then i sprayed the coil cleaner and went back with a hose (hot water) lots of dirt fell off it. simple fix learning experience. and i also went back recently and checked the condition of the system running ok without letting the customer know i re-adjusted the time for defrost to 30 mins. customer seems happy boss is happy. i guess until i screw up again.
    Get er Done!

    Do what has to be done
    when it has to be done
    as well as it has to be done
    And doing it all the time.

  7. #7
    Join Date
    Jun 2004
    Posts
    854
    If box is not very tight
    Gaskit bad,box leaking air
    It will freeze very fast like Spaceman said when its very humid.

    I always make sure termination is working when I adjust it any longer than 30 min

  8. #8
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    18,556
    Many freezers use 40 mins from the factory, and four defrosts cycles in 24 hours. Check what your manufacturer recommends for your geographic area.

    If you have a mechanical paragon-type defrost timer, kill the power and take the timer mechanism out of the metal enclosure. Check the mechanical linkage on the back side, as that solenoid and the operating arm is what takes the unit out of defrost when the termination contacts close. I was stunned the first time I found broken parts back there, but it kept the unit from working as it should.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

    AOP Forum Rules:







  9. #9
    Join Date
    Jul 2012
    Location
    Western KY
    Posts
    1,221
    40 min is fine so is 20 min. DTS should cycle it out of defrost not time anyway. If it can't have all frost gone within 20 min there is a problem, to much frost or bad heaters etc. rarely see walk ins with door switches to cycle fans, good idea but rarely used, in my area anyway.

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