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Thread: Pressure Switch Bypass

  1. #1
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    Pressure Switch Bypass

    First off, I am just learning the trade. I got in to help a church buddy with the business. My hours are flexible so I had the time to help him out, being his hands and legs and eyes, as he had almost no use of his right arm. Then a month later he passed away. I'm still learning, with some help with a biker brother (BB) in the business and the owner's son (OS).

    I came across a system with some weird numbers and talked to the boss's son, who knows quite a bit. High subcooling, high superheat, high vapor pressure (to me, based on the high side), low liquid pressure. He said to add more refrigerant. Nope, BB looks at it and says either bad compressor or TXV. Do a pump down. Checked youtube to double check pump down procedures, AC tech training channel (Craig Migliaccio or AC Service Tech). Had a wire to bypass the high and low pressure switches.

    Thought, why not add a switch to the line to be able to cut out the compressor and a connection like the WAGO on the tail to connect to the thermostat connection? Can also use it anytime one needs to turn the unit on and off while working on it, such as startup testing the capacitor.
    https://www.menards.com/main/electri...6964930&ipos=2

    Or does such an animal already exist?

  2. #2
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    Generally it is called a jumper wire.

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  4. #3
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    I'm not big on jumping out low pressure safeties but what kind of compressor was this if it was a scroll I'd say definitely don't do that as I don't think it would really show you anything.
    "Is this before or after you fired the parts cannon at it?" - senior tech
    I'm tired of these mediocre "semi flammable" refrigerants. If we're going to do it let's do it right.
    Unless we change direction we are likely to end up where we are going.

  5. #4
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    High and low pig tail safeties are available.

    You have other issues to address first, not just one.

  6. #5
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    Quote Originally Posted by RedSafety View Post
    First off, I am just learning the trade. I got in to help a church buddy with the business. My hours are flexible so I had the time to help him out, being his hands and legs and eyes, as he had almost no use of his right arm. Then a month later he passed away. I'm still learning, with some help with a biker brother (BB) in the business and the owner's son (OS).

    I came across a system with some weird numbers and talked to the boss's son, who knows quite a bit. High subcooling, high superheat, high vapor pressure (to me, based on the high side), low liquid pressure. He said to add more refrigerant. Nope, BB looks at it and says either bad compressor or TXV. Do a pump down. Checked youtube to double check pump down procedures, AC tech training channel (Craig Migliaccio or AC Service Tech). Had a wire to bypass the high and low pressure switches.

    Thought, why not add a switch to the line to be able to cut out the compressor and a connection like the WAGO on the tail to connect to the thermostat connection? Can also use it anytime one needs to turn the unit on and off while working on it, such as startup testing the capacitor.
    https://www.menards.com/main/electri...6964930&ipos=2

    Or does such an animal already exist?
    Never Ever bypass a Safety unless your there to act as that safety and accept the responsibility.

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  8. #6
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    Customer will find it, destroy the equipment and blame you.

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  10. #7
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    Thread Starter
    But a quick way to test the pressure switches. NOT looking at leaving it in the system, just quick diagnosis when everything else looks good.

    The particular system in question on the pump down, the manufacturer approves pump down on the unit.

  11. #8
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    Quote Originally Posted by RedSafety View Post
    But a quick way to test the pressure switches. NOT looking at leaving it in the system, just quick diagnosis when everything else looks good.

    The particular system in question on the pump down, the manufacturer approves pump down on the unit.
    Thats what your volt meter is for!

    If the HP opens find out why, same for LP.

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  13. #9
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    As pecmsg said, NEVER ever walk away from a unit with a safety bypassed.


    Quote Originally Posted by pecmsg View Post
    Never Ever bypass a Safety unless your there to act as that safety and accept the responsibility.
    I do a triple evac with nitro to remove non condensables.

    I'm feelin' a little peculiar.

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  15. #10
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    Quote Originally Posted by pecmsg View Post
    Thats what your volt meter is for!

    If the HP opens find out why, same for LP.
    On the system I was going to pump down, it would have been a major teardown to get to them. Very user and technician UNfriendly design. On the other systems I've worked on, yes, a meter would be a quick and easy check.

  16. #11
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    Quote Originally Posted by RedSafety View Post
    On the system I was going to pump down, it would have been a major teardown to get to them. Very user and technician UNfriendly design. On the other systems I've worked on, yes, a meter would be a quick and easy check.
    and why do you have to get to them for pumping down?

    Aren't they accessible in the control box?

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  18. #12
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    Jumpering a low pressure switch is a good way to pump oil out of any compressor, especially if you`re not around to monitor operation. Other controls to compensate for that are at best unreliable.

  19. #13
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    Quote Originally Posted by hvacgaspiping View Post
    Jumpering a low pressure switch is a good way to pump oil out of any compressor, especially if you`re not around to monitor operation. Other controls to compensate for that are at best unreliable.
    Tell that to all the manufacturers that don't put low pressure switches. I add low pressure switches every time I get a chance. It drives me nuts that some manufacturers don't include them and that people bypass them.
    "Is this before or after you fired the parts cannon at it?" - senior tech
    I'm tired of these mediocre "semi flammable" refrigerants. If we're going to do it let's do it right.
    Unless we change direction we are likely to end up where we are going.

  20. #14
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    Quote Originally Posted by hvacgaspiping View Post
    Jumpering a low pressure switch is a good way to pump oil out of any compressor, especially if you`re not around to monitor operation. Other controls to compensate for that are at best unreliable.
    How exactly does that work?

    I've seen many compressors that ran in a vacuum for years!

  21. #15
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    Quote Originally Posted by pecmsg View Post
    How exactly does that work?

    I've seen many compressors that ran in a vacuum for years!
    Yeah it seems like recycling on low pressure safety is a lot more likely to cause it than not having a low pressure safety.
    That's why I had a lock out relay every chance I get.
    "Is this before or after you fired the parts cannon at it?" - senior tech
    I'm tired of these mediocre "semi flammable" refrigerants. If we're going to do it let's do it right.
    Unless we change direction we are likely to end up where we are going.

  22. #16
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    I know where a Rheem classic unit is I don't know the age because the data plates gone or maybe I should say long gone but a couple times a year it runs low and sits there running with no safeties at 10° section saturation temperature or lower with extremely high superheat and 155° condensing temperature oftentimes because the only time it gets serviced is when it quits cooling and I get sent out to make it cool again. Is that darn thing just won't quit. This year I told them just replace it because r22 is too expensive to charge it up but I'm not sure what they did because I keep driving by and seeing it still running like always so I guess somebody probably topped it off with some r22 alternative or something.
    I seen running low one time kill LG scrolls so all compressors are not made equal.
    "Is this before or after you fired the parts cannon at it?" - senior tech
    I'm tired of these mediocre "semi flammable" refrigerants. If we're going to do it let's do it right.
    Unless we change direction we are likely to end up where we are going.

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