A9 valve?
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Thread: A9 valve?

  1. #1
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    A9 valve?

    got a hussmann rack with (no cool gas defrost)all off time. my A9 valve is closed
    my liquid level gauge aways goes from 0 to 45% its never stable i opened the A9 to see how it does i left it at 190 psi my condenser set.point is 220 its a 404a rack. is this valve needed at all or can i leave it closed i know it applys pressure to the tank to push the gas out during cool gas defrost.could this make my level go up/down?

  2. #2
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    Jun 2001
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    I would get the receiver level at 20-30% with all systems calling.

    I think your receiver is jumping up due to systems off and LLSV's denergizing, liquid is backing up into receiver and then when all of the circuits are calling you go to zero in the receiver since the liquid needs to move from receiver to circuits. And I am only responding in the way you posted. If it aint that then we need more info. For example. Is this a flow through or is it a surge style of receiver?

    I'd set the rack head pressure as low as possible, which right now in florida, I doubt she can drop below about 180 in the ambient you have at the moment.

    I think most hussman racks of newer 404 design want to see a fan cycle head pressure at 205, Hold Back set for 200 and the receiver bypass at 195.

    But I also think hussman only uses that as a guide that a guy could use and be safe. There should be engineering specs on the rack inside the control cabinet and they will state their desired range of head pressure. Some guys think that is the bible, but I have been lucky with departing from that a little.

    I just set 2 new hussy racks. and I got my head down to about 160 with out going in the toilet. So. I then picked 180 as my benchmark for fancycle, 175 for hold back and 170 for receiver. And we will see how she does here over the next few weeks. I have the perfect weather at the moment to be seeing if my setpoints are good or need to be tweaked a bit since my ambients are ranging up and down by 50 degrees.

    And remember, amount of liquid is important. As you set your controls, some refrigerant may need to be added. Some might even be able to be taken out.

    Anytime you see your head all dicked up from the last ten idiots, you kinda gotta start from scratch.

    I have gone on leaks, and had to add refrigerant to get things online, then end up having to set the whole friggin rack up so it runs correctly.

    Lots of times, guys getting rushed and set something to get it by, hoping to return, then never being able to get back. Then that goes on for 3 years and now your the poor shmuck who is gonna need to make it right.

    Anytime you see a receiver jumping, one thing is for sure, you have to see the receiver and column of liquid when everything is calling to see if you may need more refrigerant.

  3. #3
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    Quote Originally Posted by gatorfan9606 View Post
    got a hussmann rack with (no cool gas defrost)all off time. my A9 valve is closed
    my liquid level gauge aways goes from 0 to 45% its never stable i opened the A9 to see how it does i left it at 190 psi my condenser set.point is 220 its a 404a rack. is this valve needed at all or can i leave it closed i know it applys pressure to the tank to push the gas out during cool gas defrost.could this make my level go up/down?
    Its funny how I end up at the same settings as Dowadudda. Sounds like a surge rack , I use the hand method, close the ball valve to the A9, let it cool down, back the valve off untill completely closed, put your hand downstream of the valve and slowly open untill it just starts to get warm, leave it alone.

    Too test this setting, shut off all pumps,(simulate a power failure) wait 20 mins, restart system normally. If the bypass is set too high the rack will go off on high head pressure, very common. I get racks locked up like that all the time, Some of these guys actually read the hussmann book and try to set the valve.

    Dowadudda is very correct on the rest of the settings, I like the 160 (even as low as 140 with ballanced port valves and no hot gas) it does work.

    Dowadudda how are you setting the duel holdback valve or is this just something common to my area?

  4. #4
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    [QUOTE=Dowadudda;2000037]I would get the receiver level at 20-30% with all systems calling.

    I think your receiver is jumping up due to systems off and LLSV's denergizing, liquid is backing up into receiver and then when all of the circuits are calling you go to zero in the receiver since the liquid needs to move from receiver to circuits. And I am only responding in the way you posted. If it aint that then we need more info. For example. Is this a flow through or is it a surge style of receiver?

    I'd set the rack head pressure as low as possible, which right now in florida, I doubt she can drop below about 180 in the ambient you have at the moment.

    I think most hussman racks of newer 404 design want to see a fan cycle head pressure at 205, Hold Back set for 200 and the receiver bypass at 195.

    But I also think hussman only uses that as a guide that a guy could use and be safe. There should be engineering specs on the rack inside the control cabinet and they will state their desired range of head pressure. Some guys think that is the bible, but I have been lucky with departing from that a little.

    I just set 2 new hussy racks. and I got my head down to about 160 with out going in the toilet. So. I then picked 180 as my benchmark for fancycle, 175 for hold back and 170 for receiver. And we will see how she does here over the next few weeks. I have the perfect weather at the moment to be seeing if my setpoints are good or need to be tweaked a bit since my ambients are ranging up and down by 50 degrees.

    And remember, amount of liquid is important. As you set your controls, some refrigerant may need to be added. Some might even be able to be taken out.

    Anytime you see your head all dicked up from the last ten idiots, you kinda gotta start from scratch.

    I have gone on leaks, and had to add refrigerant to get things online, then end up having to set the whole friggin rack up so it runs correctly.

    Lots of times, guys getting rushed and set something to get it by, hoping to return, then never being able to get back. Then that goes on for 3 years and now your the poor shmuck who is gonna need to make it right.

    Anytime you see a receiver jumping, one thing is for sure, you have to see the receiver and column of liquid when everything is calling to see if you may need more refrigerant.[/QUOTE
    i have seen 404a just sit in the condenser at 180psi and my sightglass flashes like crazy.i just dont know why it does that but it does even if i run my A8 on bypass thats why i have it at 225psi i had all my sorits active when i checked the level so nothing was on defrost at the time.now it a twin reciever set-up not a surge tank a (flow through)i did a spot check here and there on s-heat on some cases i went back today and its still going up&down?

  5. #5
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    sorits can do that. I don't know why, but I swear I read your post and thought you said you had all LLSV for control. My mistake.

    You might be seeing the "lazy river" in your sight glass, due to low load, not so much that it's true flash gas. There is a term for it. It's called laminar flow. Actually some very good discusions about this very anomally at refrigeration engineer dot com. During periods of time when your sorits are all closing down and you start to see this swash bucket effect.

    Up and down receiver level is very common with sorits all along the manifold as well.

    I'd try to get your receiver to never fall below 15 to 20%. If it goes to 60, so what. As long as she only see's a minimum of 15 to 20%. Set your head the way I explained. And in this ambient, you should not even be in play with your hold back and ord valves. Shouldn't even be thinking of them. Alot of guys think to fiddle with them when having issues like your describing but it's the wrong direction to think.

    Hold Back is to stack liquid, by reducing the effective condenser surface area, to elevate head pressure in low ambient conditions. The receiver valve, I call all of them ord, (which is the wrong terminolgy) is to keep receiver pressure from falling below the basement threshold you decide is the correct basement pressure. anywhere between 5 to 30 psi below what hold back is set for. Hussman wants to see 5 psi difference. I have seen as much as 45 in my travels.

    (basement is what the design delta p is for the TXV's). A rule of thumb is to stay above 100 psi difference between suction and head pressure.

    This ord valve should and only will come into play, when there is a pressure difference between drop leg and receiver pressure due to the hold back in play. It's for the ability to keep liquid manifold pressure sufficient while we are doing the best we can with elevating head with hold back and experience pressure penalty in the receiver and liquid manifold.

    So both these valves have little to do with your problem and having nothing to do with resolving your problem.

  6. #6
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    frigeguy,

    I have never had the pleasure of setting twins. I have seen them. Just never was on a call for them. I never really understood the strategy of thought to pipe two hold backs in paralel like that. Can you enlighten me?

    How do you set them?

  7. #7
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    Quote Originally Posted by Dowadudda View Post
    frigeguy,

    I have never had the pleasure of setting twins. I have seen them. Just never was on a call for them. I never really understood the strategy of thought to pipe two hold backs in paralel like that. Can you enlighten me?

    How do you set them?
    its twin receivers one hold back valve. i will lower my setpoint give it a whirl
    some guys told me they've seen this problem before they added more gas to the system. am peeking 45% thats pretty good.i've seen these A8-A9 valves even bypass because they never come to play down here

  8. #8
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    You might even have a bad liquid level guage ,who knows.

  9. #9
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    Mar 2008
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    Originally Posted by Dowadudda
    frigeguy,

    I have never had the pleasure of setting twins. I have seen them. Just never was on a call for them. I never really understood the strategy of thought to pipe two hold backs in paralel like that. Can you enlighten me?

    How do you set them?

    Its one holdback with 2 setpoints, usually 2 5/8. Found on Hussmann. It's used to bring up head pressure during heat reclaim or dehumidification. Only used on surge . I've been setting the Hussmann as low as 140 on the primary and 170 - 180 on the secondary, Depends on the TXV's in the store. Older TXV's require a greater differential across them, but the newer stuff works fine at 140(404A) as long as all the valves are ballance port. Were taking advantage of the subcooling up here. Outside air temperatures fall as low as -15f -20f. The idea is to run the head low as much as possible then boost it up during heat reclaim. Low temp racks set up a bit higher with 160 min and again 180 during heat reclaim. I also see a difference on the condensor, The first two fans being 1/2 hp with a different blade, some of the plus II systems used variable speed fans for the first set.

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