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  1. #1
    Join Date
    Aug 2006
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    Colorado
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    310

    Question Freezer: two evaporaters, one condensing unit: How to terminate?

    Okay, so I inherited a store where the freezer (walk in) has had constant freezing problems. So to cut to the chase, both evaporators have termination/fan delay switches. One evaporator was cranking cold, and the other was just so so. The so so evaporator was terminating before the other one could melt all the frost buildup, thus a glacier was forming on the evaporator. So I adjusted the txv so that both evaporators are blowing about the same temp difference across the coil, and I replaced the defrost termination switches in both units so at least they matched. My question is: What do you guys like to do for termination in a system with 2 evaporators working off of one condensing unit.
    I can't say that I have come across this problem before. I thought 2 evaporators off of one unit usually had EPR valves on them........

  2. #2
    Join Date
    Aug 2002
    Posts
    70
    Are the fan delays wired in series so that both have to warm up before overriding the time clock?

  3. #3
    Join Date
    Aug 2006
    Location
    Colorado
    Posts
    310

    Nope

    Nope, which ever one goes first trips the clock. I thought about the series thing, but wouldn't that require a 3rd termination switch? Because one of them is always going to trip 1st......

  4. #4
    Join Date
    Oct 2011
    Location
    Chicagoland Area
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    Quote Originally Posted by tuba View Post
    Nope, which ever one goes first trips the clock. I thought about the series thing, but wouldn't that require a 3rd termination switch? Because one of them is always going to trip 1st......
    I don't know that a 3rd switch is what you'd need. A relay would accomplish what you're thinking of. Have 1 switch energize the coil on the relay and the second switch, when it closed, would send power to the relay contacts, and the other side of the contact energizes the X terminal. That setup would IMO ensure both termination switches closing to terminate the defrost. Just make sure the heater safeties are operational.
    Officially, Down for the count

    YOU HAVE TO GET OFF YOUR ASS TO GET ON YOUR FEET

    I know enough to know, I don't know enough
    Liberalism-Ideas so good they mandate them

  5. #5
    Join Date
    Aug 2006
    Location
    Colorado
    Posts
    310

    Thumbs up tHANKS!!!

    Thank you! That one has stumped my brain for a loooong time. I will see about doing that the next time I have some approved work there.

  6. #6
    Join Date
    Aug 2008
    Location
    Burlington , Mass
    Posts
    470
    Both switches in series is all thats needed. It would take both to terminate the defrost.
    I'll be there when I get there and not a minute later

  7. #7
    Join Date
    Oct 2011
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    Chicagoland Area
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    Quote Originally Posted by BURL-REF View Post
    Both switches in series is all thats needed. It would take both to terminate the defrost.
    If these are 3 wire switches, how would you accomplish that?
    Officially, Down for the count

    YOU HAVE TO GET OFF YOUR ASS TO GET ON YOUR FEET

    I know enough to know, I don't know enough
    Liberalism-Ideas so good they mandate them

  8. #8
    Join Date
    Mar 2009
    Location
    Mid-Mo
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    3,596
    This may be overkill but you might try something like this:

    http://www.ke2therm.com/productsevap.html

    Those who have installed them are giving pretty good feedback. I personally haven't put one in but I'm dying to.

  9. #9
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,434
    Heatcraft's Refrigeration Systems I&O Manual has a lot of good wiring diagrams for this. Check out p.41 (Diagram 3).
    http://www.heatcraftrpd.com/products...5CH-IM-64L.pdf

    It shows how to connect the 3-wire fan delay/termination Klixons in series with no relays needed.

  10. #10
    Just take the termination switch out of the evaporator that terminates defrost first. Of course that's assuming that the same evap always trips first. But this solution sounds like the easiest to me.

  11. #11
    Join Date
    Mar 2009
    Location
    Mid-Mo
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    Quote Originally Posted by icemeister View Post
    Heatcraft's Refrigeration Systems I&O Manual has a lot of good wiring diagrams for this. Check out p.41 (Diagram 3).
    http://www.heatcraftrpd.com/products...5CH-IM-64L.pdf

    It shows how to connect the 3-wire fan delay/termination Klixons in series with no relays needed.
    That's good stuff, that answered some other questions that I had aside from what we were talking about.

  12. #12
    Join Date
    Aug 2006
    Location
    Colorado
    Posts
    310

    Wink Thanks Icemeister

    Thank you Icemeister. I knew it could be done, but this brain has so much hvac/refrigeration stuff mixed up in it that things get blurry. That is the down side of working for a company that does both. I may not put my hands on a freezer for a couple of months, then I will get 3 or 4 of them that the other guys could not figure out.

  13. #13
    Join Date
    Jul 2004
    Location
    NJ
    Posts
    1,795
    Quote Originally Posted by icemeister View Post
    Heatcraft's Refrigeration Systems I&O Manual has a lot of good wiring diagrams for this. Check out p.41 (Diagram 3).
    http://www.heatcraftrpd.com/products...5CH-IM-64L.pdf

    It shows how to connect the 3-wire fan delay/termination Klixons in series with no relays needed.
    Hi Ice,
    on page 42, for unit 'cooler b' there is no fan delay. The unit fan contactor works off of the 'unit a' fan delay. It seems like a flaw in the series wiring of the 3 wire controls. Am I seeing it right?

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