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  1. #1
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    Modifying/troubleshooting Porkka walk in freezer



    Hi! I recently got an about 15+ years old Porkka 3000 walk in freezer. I had the refrigeration unit serviced by a supposedly qualified tech, and installed it later in the walk in cabinet. The problem was that due to a defective temp sensor the evap. fan would not start. The sensor was no longer available, and the tech just short circuited it. I`m not sure what the sensor function was, but I can enclose a circuit diagram here later if anyone would look at it.

    The freezer then seemed to work fine, temp reached -20C, and after a while the defrost cycle started, and I could feel that the evap. bottom tray heater got warm. Then the next day I noticed that the freezer was stopped, and the fuse for that circuit was blown. I reset the fuse, and the freezer stated normally again. When the defrost cycle started I noticed that the bottom tray heater no longer got warm.

    I inspected the mechanic timer, and noticed that it lagged a lot, and that the defrosting time was probably 2-3 hours. I also had a look at the electrical contacts of the timer, and they looked bad.

    I then replaced the mechanical timer with a Dixell electronic controller (from eBay), but still no heat. From studying the circuit diagram it seems that there is a overheat sensor in series with the heater element.
    So if this is open circuit the heaters will not work.

    If I remove the evap. fan cover I see a large bulb with a cappilary tube (is this the right term?), sitting just inside the fan cover, not in contact with the evaporator. Is it likely that this is the overheat sensor? It is very difficult to see what else is inside the evap. area, and I don`t know how much I can move the evaporator without damaging anything?

    Cappillary tubes from the room sensor and the one that I think might be the over temp sensor leaves the cabinet through a hole in the wall (see picture, covers removed), and goes to a box (controller?) outside near the compressor. It is not easy to get to this box without removing the refrigeration unit, but it might be possible.

    With the Dixell controller I got a room sensor and a evap. sensor, so I should be able to get rid of the original sensor(s).

    Hopefully someone here has worked on a freezer like this, and can provide some advice...

    Gunnar
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  2. #2
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    Re: Modifying/troubleshooting Porkka walk in freezer

    Today I had a closer look at the capillary thermostat that I think is the defrost overtemp thermostat. Its a Teddington rather big blue box, see picture. This has a cable that goes into a connection box. What a wire spaghetti! It is difficult to reach from the side, as the compressor and condenser is in the way. But I`ve located the terminals where the thermostat is connected, and disconnected the thermostat. I`ll make a short jump wire tomorrow to check if the defrost heaters work when the thermostat is bypassed.

    Gunnar
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  3. #3
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    Re: Modifying/troubleshooting Porkka walk in freezer

    No success with the jump wire. Talked with the tech, and he told that it is possible to pull out the evaporator much further than I thought. I did, and the connection box for everything inside the evaporator casing could be exposed. I checked the heaters with an ohm-meter, and they seemed to be ok. Disconnected the wiring and connected the heaters directly to the mains, and both heaters worked! one of the heating rods through the evaporator didn`t work, but after cleaing the wiring terminal everything seems to be ok. The insulation on the wiring from the heaters and to the outside of the cabinet has burnmarks. I removed some of the insulation, and the inside is ok. Something close to the wiring have been very hot. Will check the wiring all the way through, and put everything together again.

    Gunnar
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  4. #4
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    Re: Modifying/troubleshooting Porkka walk in freezer

    With your new dixell controller you may be able to use it to delay the fan as original. Often they are set to prevent the fan from running until the evaporator is below freezing to stop any water drops being blown off after defrost. The dixell may also be able to control the defrost timing too, depends on model.

  5. #5
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    Re: Modifying/troubleshooting Porkka walk in freezer

    Yes, it is connected to take care of defrost and fan delay, but the defrost doesn`t work. But now I have cleaned the wire terminals, cut of the part of the wires with burned insulation, and connected everything again. Also checked the wiring all the way through to the Dixell, so if the heating doesn`t work now...

    Will power up tomorrow!

    Gunnar

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    Re: Modifying/troubleshooting Porkka walk in freezer

    I wouldn't be surprised to find a faulty defrost heater on a 15 year old unit, i would test them for a short to earth, resistance through the heater, and if that checks out i'd test them with an amp meter to see how much current they pull, i have seen heaters that are ok cold but go faulty when warmed up!

    Good luck

  7. #7
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    Re: Modifying/troubleshooting Porkka walk in freezer

    Thanks! I did check the heaters, both with an ohm-meter, and also by connecting to the mains directly. Both the tray and the evaporator heaters seems to work fine now.

    Do you know the power rating these heaters use to have?

    Gunnar

  8. #8
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    Re: Modifying/troubleshooting Porkka walk in freezer

    in my opinion, what i would do is rip out all that wiring and stats, fit a lae controller or eliwell controller,fit the probe 2 into the top right hand of the coil as far from the heater as possible, fit probe 1 onto the air return.
    fit 2 contactors 1 for your heaters and 1 for the compressor and condenser fan, control the evap fan through the controller contacts, looking at the attached pictures there are more probes,stats and capilarys than anything, just rip it all out and start again, or you will just end up chasing your tail.

  9. #9
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    Re: Modifying/troubleshooting Porkka walk in freezer

    It works! Except that the mains fuse blew once yesterday when the defrost cycle was over, and the evap. fan started again. Reset the fuse, and it has not happaned again. Could be an earth fault in the heaters. The mains fuse has a 30mA earth fault detector.

    Gunnar

  10. #10
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    Re: Modifying/troubleshooting Porkka walk in freezer

    Quote Originally Posted by coolhibby1875 View Post
    in my opinion, what i would do is rip out all that wiring and stats, fit a lae controller or eliwell controller,fit the probe 2 into the top right hand of the coil as far from the heater as possible, fit probe 1 onto the air return.
    fit 2 contactors 1 for your heaters and 1 for the compressor and condenser fan, control the evap fan through the controller contacts, looking at the attached pictures there are more probes,stats and capilarys than anything, just rip it all out and start again, or you will just end up chasing your tail.
    Sorry, didn`t see your post before posting. But I agree, I would be happy to get rid of all the old stuff, and do the setup from the Dixell controller that is already in place. So far it is only taking vare of the defrosting and temperature display.

    But everything has been working fine since my last posting , and I`ve been busy with other projects..

    But I have a question: What is the expected on/off dutycycle when everything works as expected? Currently the freezer runs for about 5 minutes, and then stays off for about 10 minutes. Temperature when turning on is about -17.5C, and it turns off again at about -22C.

    Gunnar

  11. #11
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    Re: Modifying/troubleshooting Porkka walk in freezer

    Quote Originally Posted by cyberkul View Post
    Sorry, didn`t see your post before posting. But I agree, I would be happy to get rid of all the old stuff, and do the setup from the Dixell controller that is already in place. So far it is only taking vare of the defrosting and temperature display.

    But everything has been working fine since my last posting , and I`ve been busy with other projects..

    But I have a question: What is the expected on/off dutycycle when everything works as expected? Currently the freezer runs for about 5 minutes, and then stays off for about 10 minutes. Temperature when turning on is about -17.5C, and it turns off again at about -22C.

    Gunnar

    that sounds perfect!!

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