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  1. #1
    Join Date
    Mar 2012
    Location
    Rancho Cucamonga, CA
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    2

    Student With A Question.

    Hi everyone my name is jesse and i have been going to school since last october. My teacher wants us to ask a professenal "What will happen if you do a pump down while in defrost".
    He gave us two different wiring diagrams where on one of them the LP, HP, and CC are wired directly to the L1 and L2. As where the other diagram is wired into the defrost time clock. Can anyone help me out on here, am i just missing something? He wants us to tell him what the worst case senario will be having it wired directly to L1 and L2.

  2. #2
    Join Date
    Apr 2012
    Location
    winnipeg
    Posts
    1,330
    Hi Jesse ..first of all you need a liquid line solenoid for a pump down system.... not really understanding your wording... try again and I am quite sure someone will try and help you..
    it was working.... played with it.... now its broke.... whats the going hourly rate for HVAC repair

  3. #3
    Join Date
    Dec 2002
    Location
    SouthEast NC ICW & Piedmont Foothills
    Posts
    7,635
    if those controls are not line voltage-you just let the magic smoke out.
    It`s better to be silent and thought the fool; than speak and remove all doubt.

  4. #4
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,048
    A pump down will not work in defrost because the large line (suction in cooling) is discharge of the compressor in defrost (heat mode) pump down will only work in cooling mode and you will need to jump out lp switch do fully pump down to deminimus amount of refrigerant, doesn't matter if the safety is wired to board or in series directly with contractor coil.

  5. #5
    Join Date
    Oct 2004
    Location
    Central WA
    Posts
    1,534
    @ Jesse: Kind of a vague description and we need to get the whole story to determine an outcome. Can you post a pic of the diagrams? Also, when you do tell us what you think will happen and why. Then, when you get answers try to apply what you are being told. Walk each scenario through the diagram and determine if you are being fed a load of bs or not.

    @ carmon: All you need to manually pump down a refer system is a receiver with a king valve and a service wrench. A/C split systems don't even have the receiver, just valve it off and pump into the condenser coil.

    @ jtrammel: Sounds more like a refer question to me rather than a heat pump as he references the time clock rather than a board.

  6. #6
    Join Date
    Feb 2005
    Location
    Dothan, Al
    Posts
    3,453
    Jessie,

    Though I don't understand your instructors wisdom for the question, except maybe to make you think....
    When in defrost, a heat pump SHOULD do 3 things.
    1) place system in cooling cycle
    2) turn on auxillary heat
    3) turn OFF outdoor fan.

    So, if you were to try & pump the system down, ( close liquid line valve ) ,while it was already into the defrost cycle, the refrigerant would be pumped into the outdoor coil ( as in a normal cooling cycle pump down), however, with the outdoor fan off, the head pressure would increase rapidly, probably causing the high pressure switch to stop the compressor ( this would depend on how much ice was on the coil & the time it stayed in defrost & the outdoor temps)

    This then begs the question of....what would then happen if the system reverted back to heat cycle while you were still trying to pump down?

    Hope this helps some,
    Richard

  7. #7
    Join Date
    Jul 2012
    Location
    Western KY
    Posts
    1,221
    If he is talking refrigeration, walk in cooler/freezer, system would most likely be pumped down at start of defrost cycle if it's electric or air over defrost. So comp would be off on low pressure switch. Need wiring diagrams to see what exactly your teacher is looking for. There are alot of different systems with alot of different control set ups and alot of different defrost schemes. We just throwing darts in the dark with the info provided.

  8. #8
    Join Date
    Apr 2012
    Location
    winnipeg
    Posts
    1,330
    Quote Originally Posted by cjpwalker View Post
    @ Jesse: Kind of a vague description and we need to get the whole story to determine an outcome. Can you post a pic of the diagrams? Also, when you do tell us what you think will happen and why. Then, when you get answers try to apply what you are being told. Walk each scenario through the diagram and determine if you are being fed a load of bs or not.

    @ carmon: All you need to manually pump down a refer system is a receiver with a king valve and a service wrench. A/C split systems don't even have the receiver, just valve it off and pump into the condenser coil.

    @ jtrammel: Sounds more like a refer question to me rather than a heat pump as he references the time clock rather than a board.
    Really, never new that...how did I survive in this trade for 30 years
    it was working.... played with it.... now its broke.... whats the going hourly rate for HVAC repair

  9. #9
    Join Date
    Oct 2004
    Location
    Central WA
    Posts
    1,534
    I don't know... You must have put in a lot of solenoid valves so that you could pump down systems?

  10. #10
    Join Date
    Sep 2004
    Location
    Kansas City, Kansas, United States
    Posts
    13,833
    Lol

  11. #11
    Join Date
    Apr 2012
    Location
    winnipeg
    Posts
    1,330
    Quote Originally Posted by cjpwalker View Post
    I don't know... You must have put in a lot of solenoid valves so that you could pump down systems?
    Yes I have probably thousannds
    it was working.... played with it.... now its broke.... whats the going hourly rate for HVAC repair

  12. #12
    Join Date
    Mar 2012
    Location
    Rancho Cucamonga, CA
    Posts
    2
    thank you for all your help but i cant seem to find a way to upload the picture of the diagram

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