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  1. #1
    Join Date
    Aug 2006
    Location
    Colorado
    Posts
    309

    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
    309

    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
    Posts
    4,625
    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

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  5. #5
    Join Date
    Aug 2006
    Location
    Colorado
    Posts
    309

    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

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