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  1. #27
    Join Date
    Sep 2001
    Location
    East Stroudsburg, PA
    Posts
    13,215

    Hey, Bud

    If you know how to wire a thermostat to turn the compressor on and off, you ALREADY know how to wire the tstat to control a Liquid Line Solenoid valve.

    Pretend that the valve is the compressor contactor, and set your LPC to cut out at about 15, and cut back in at about 25.

    When your tstat opens, (Shuts off) the Liquid Line Solenoid coil will deenergize, which closes the valve itself, which will cause the refrigerant in the evaporator to pump into the receiver and condenser, until the LPC "opens" (shuts off) the compressor contactor, turning off the compressor.

    As the box temp rises, and the tstat "closes", it OPENS the valve, by powering up the solenoid coil, and the whole process starts all over.

    Here is an abbreviated list of what you'd need to do:

    • Cut in a liquid line solenoid valve (rated greater than the entire system tonnage- REAL easy on a small system like you have.) right before the coil.
    • Install a thermostat (Close-on-rise, like a Penn A19) near the solenoid valve, preferably near the BACK (Inlet air side) of the evaporator.
    • Find a power source for the tstat and solenoid. (This can come from the evap fans, if no other source is available, although a separate source is much preferred.) It does NOT have to connect in any way, shape or form to the condensing unit.
    • Wire the "hot" to one side of the stat, then take this "hot" from the other side of the stat, and get it to the solenoid coil.
    • Wire the L2 or "neutral" (depending on the voltage. I'm assuming 115, but 230 is also common...) direct to the solenoid coil. (Other wire in coil, not already occupied by the "hot".)
    • Connect the ground whereever there is a place to connect it. (The stat and the coil should have grounding screws already in place.)
    • Turn all this **** ON.
    • Set the tsat to 35 degrees or so.
    • LOWER THE LPC SETTING TO 15-25, like I said above. {NOTE: The LPC is STILL turning the compressor on and off, but only on a "command" provided by a low suction pressure condition caused by the tstat turning the coil off!!!}
    • Get paid.
    • Go home.
    • Repent your sins.


    The entire process sounds intimidating, until you've actually done it.

    The parts are relatively inexpensive, and you don't have to CHANGE A DAMN THING, other than the setting on the low pressure switch.

    I could do this whole thing, vacuum and all, in a real limited-access cooler, in about 2-3 hours, but I've done it a few times before...

    Print this out, go unf*ck that thing, and make the customer happy.

    You might want to discuss the bill with your boss before you hand it to the customer, as he may want to knock some off of it for all the excess time. That is OK. I'd worry if he didn't. Remember, he THREW your sorry ass into this mess while he was filling up the G-string of some worn out stripper near some airport. He should expect to cover some of that bill.

    .Have fun


  2. #28
    Join Date
    Aug 2002
    Location
    Orange County CA
    Posts
    1,084
    Dave , you are a patient man

  3. #29
    Join Date
    Sep 2001
    Location
    East Stroudsburg, PA
    Posts
    13,215
    Did I actually use the word "abbreviated"????

  4. #30
    Join Date
    Sep 2001
    Location
    East Stroudsburg, PA
    Posts
    13,215
    Originally posted by NedFlanders
    Dave , you are a patient man
    Note that my phone number appears nowhere in that entire post.

  5. #31
    Join Date
    Aug 2004
    Location
    chicago
    Posts
    123
    thanks again for info everyone, i explained to the costumer about the pumpdown valve and that it should be installed,the manager said it seems to work fine so well give it some time and if we have trouble well go ahead with it,

    i put on a tstat since i bought one anyway, i had one service call prior to this on a walk but some idiot turned turned the tstat down to -30 degrees and left the dooor open because the air conditioning wasnt working and never turned it back up, i had 2 york rooftops to clean the evap and consensore coils, the cooler condensor was on the roof too, it put the tstat back to 35 and it seemed to cycle fine as i was watching while cleaning the coils, and they havent called back yet,

    On the cooler i posted with the trouble, i noticed there wasnt a tstat so picked one up when i got all the equipment to have just in case because the prior cooler had one, its in place and cycling the unit off,i told the manager to get new thermometers cause one said 38 and the 52 only 3 feet from one another, defrost timer now on 2 times a day for 60 min after searching for the pins to attach to the clock, everything seems kosher the manager said it held 35-38 with constant door opening all day and i seen minimal frost on the coil and condensation in the drain pan and at 8 am frost on the food so im guessing it was a lil colder than the thermoeter that said 38 but i didnt callibrate the differential on the tstat yet at that point

    i've done residential HVAC for 6 years now and learned on the job no schooling, then went to school thru local 399 and put all the pieces to the puzzle together so now on residential is a piece of cake, but refrigeration i havent a clue on the controlls, on a furnace i almost know the problem right away when the costumer explains what is happening

    all and all is the purpose of the pumpdown valve is to close off the liquid line at tstat cycling to get all the refrigerant back to the compressor untill the LPC shuts down the compressor ? is the main reason to get the frost and ice off the evap faster by getting the refrigerant out of the suction line?

    should i go by the costumer request on the valve(see how it runs) or tell him its mandatory

    thanks again all, im so glad i found these forums just take it easy on me, im new to refrigeration so if i ask what you think is a dub question just ignore it

  6. #32
    Join Date
    Apr 2002
    Location
    most of the time in the Philippines
    Posts
    1,207
    It sounds like this has been a good learning experience for you. Why use the T-stat/LLSV aka pumpdown control? A thermostat will control the temperature better then an LP control will and you won't have to make seasonal adjustments. I like the Ranco ETC stats. They hold their setpoints/differentials better than electromechanical t-stats and you can lock the keypad with a switch under the cover. A pumpdown system controls liquid refrigerant in the low side during the off cycle. This is especially important if the compresssor is below the evaporator coil and is mandatory on a freezer application with electric defrost. One suggestion for this job; if the customers box needs new thermometers, sell them some new ones. I would never tell a customer that it's up to them to get some new thermometers. I can repair that [at a profit of course]. Suggestions for the next time you have to do a job like this-

    1. Verify the line sizes for the refrigerant you switch to. Don't assume that the existing lines sizes will be ok.

    2. Verify the size of the nozzle in the distributor. I noticed that no one asked about it.

    3. Install a door switch. On walk in coolers, the door switch can shut off the LLSV and the evaporator fans or just the LLSV- dealers choice. On walk in freezers, the door switch has to shut off both the LLSV and the evaporator fans.

    One other suggestion- invest in a micron gauge and some deep vacuum hoses and isolation valves.


  7. #33
    Join Date
    Jun 2001
    Location
    San Diego, CA
    Posts
    1,149
    primary advantage of installing a pumpdown on a tstat is tighter temperature control. pumpdowns MUST be installed with some form of defrost control. LPC control may or may not since the control can be set to cause the coil to defrost by itself. Pumpdowns are also more able to handle heavy traffic as they turn on quicker when you open the door. In applications where temp is critical - milk etc. pumpdowns are best.

    Also, for stats - I sell Johnson Controls A419's.
    The additional settings allow for a lot of flexibility
    when dealing with 'problematic' icing.


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