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  1. #14
    Join Date
    Feb 2008
    Location
    California
    Posts
    2,064
    Are you low on refrigerant?

  2. #15
    Join Date
    Jan 2013
    Location
    Wisconsin
    Posts
    23
    15% receiver

  3. #16
    Join Date
    Jun 2001
    Location
    Michigan
    Posts
    12,077
    Yes, You have NC-2, with LIQUID FLO. So, if the drop leg temp is above 70, like it should be now in this ambient, Natures Cooling Bypass is OFF De energized and not bypassing, and the Liquid Flo is De energized and OPEN. With LIQUID FLO open, you simply are routing liquid from condenser to receiver to liquid manifold. NOW. You have an OPR, that is used to pressurize the receiver. In this configuration this is to set your minnimum receiver pressure. Obviously. But this was intended to also be the way not to have a hold back valve. If your LIQUID FLOW is OPEN, the receiver OPR could be pressurizing the reciever, now the receiver is of a high pressure than the condenser, and so liquid would begin to stack in the condenser.

    So you have to account for a few things here. You might say, well if it's cold out, and my drop leg is cold, shouldn't my NC-2 be open and liquid flow off???? Well. Not really all the time. Your Condenser Fan Stat settings have to be set up right for this all to work. The first intention is to now allow the head pressure to never go below 85 SCT. So. If your Fan cycing, if your LIQUID FLOW is open, then your OPR starts to spit and sputter maintaining low setpoint head pressure. Now you start stacking a little. Then what? Now your getting a good but load of subcooling. Maybe even enough to get that drop leg to 70 to open Natures Cooling. Now it may sound that these actions are all alternating all the time, and during the moderate temps it will.

    So. If your following all that. Now you have this other thing for liquid flow. The IPR and and Check valve. Okay. During any HOT GAS DEFROST, the LIQUID FLO and NC-2 valve have to close So bypass does not happen on nc-2 and the liquid flo closes flow. When the liquid flo closes, it makes the dropleg refrigerant route through the IPR, pushing through the Check which is 20#. So in Hot Gas Defrost, we make the drop leg route through the IPR, and so it is for keeping head pressure UP during hot gas defrost, during low ambient. That is the only thing that IPR is for. It's like a hold back valve, only doing it's thing in Hot GAS Defrost. It's maintaining head pressure during hot gas. Guys who don't work in but a$$ cold weather have a difficult time with understanding stuff like this.

    So separate this stuff.

    NC-2 on it's own is just bypassing receiver at 70 degrees or below.
    NC-2 With LIQUID FLOW - Another solenoid valve, N.O. Closed at 70 degrees or below, open above 70 degrees. It uses the same T-stat. Then the IPR and Check Around that.

    In Hot Gas. These valves de energize. Both closing flow. Now the dropleg refrigerant has to go through the IPR, which is simply keeping the head pressure at a minimum setpoint during hot gas.

    If liquid flow is open, and not in hot gas. Your minnimum head pressure is maintained by the OPR pressurizing the reciever. If the receiver pressure rises above condenser pressure, it will stack liquid in the condenser. It's to eliminate the need for a holdback valve. Simply put.

    25% of your load or less can be in defrost at any one time.

    The issues your having. I would pipe clamp temp probe the outlet of the evap coil in defrost. And then same time do it after the check valve. Then do it the branch liquid line back at the rack. If your losing liquid and starving cases when one circuit is in defrost, I wonder if your check valve in the case or where ever it is, isn't stuck. Your defrosting coil is now not delivering back condensed liquid, so your liquid manifold gets it's supply from the receiver now, cause your not pushing liquid back at a high pressure. Well, your defrosting case is stealing liquid from the system. So your receiver may be going flat. Since your not getting the liquid back from the defrosting case, the other loads are starving cause your receiver is flat.

  4. #17
    Join Date
    Jan 2009
    Location
    IRELAND
    Posts
    42
    Great posts dowadudda ,very informative,not used to low ambient systems here and very little hot gas defrosts used in supermarkets

  5. #18
    Join Date
    Jan 2013
    Location
    Wisconsin
    Posts
    23
    Wow I think my head just exploded from all that info. I do follow everything you are saying now though and the way the rack operates makes sense now. Although my receiver is not flat. At first the receiver pegs to nothing, but a minute or two into the defrost it jumps back up to 15%. All the low ambient stuff is out the door right now, its bout 80 outside. So why wouldn't a starving circuit be using the 15% available from the receiver while defrost is occuring?

  6. #19
    Join Date
    Jun 2001
    Location
    Michigan
    Posts
    12,077
    Well. Its not gonna get liquid from receiver if its working right. The liquud manifold is supplied liquid from the defrosting case. Remember the header should be at a lower pressure than the liquid coming back from the defrosting load right? I was speculating if the liquud was not returning.

    If all your othwr cases on the rack are sufficiently maintainig, during a hgdfst, I wonder if that one circuit that your hqving a problem with, maybe were not maintaining full colum and its flashing before it gets there?

  7. #20
    Join Date
    Jan 2013
    Location
    Wisconsin
    Posts
    23
    Flashing before it gets to the liquid header from the defrosting case? Or flashing before it gets out to the starving case? There is no liquid from the get go to the starving circuit beginning from the liquid header. All the lines, both suction and liquid are well insulated from rack to case as well. Nothing under 5/8" liquid lines as well. Since an OLDR would be set for a diff of 40#, as it states in the manual, if that was in place of the NO solenoid; would it be correct that the DDPR should be set for 40# since that is where the diff is being produced in this setup? Sorry if I'm throwing too many questions out there, just thinkin.

  8. #21
    Join Date
    Jun 2001
    Location
    Michigan
    Posts
    12,077
    Dude. How are the rest of the circuits getting liquid, from the defrosting case.

  9. #22
    Join Date
    Jun 2001
    Location
    Michigan
    Posts
    12,077
    Your defrosting case supplies the header with liqid during hot gas dedrost. Not the reciever liquid.
    How is it only this one circuit starves?

    Your a fellow cheesehead, dont embarass me here. LoL.

  10. #23
    Join Date
    Jan 2013
    Location
    Wisconsin
    Posts
    23
    Maybe I'll just cram some block cheese in the suction canisters and replace the oil with cheese whiz! Should do the trick huh

  11. #24
    Join Date
    Jan 2013
    Location
    Wisconsin
    Posts
    23
    You just asked me my original question by the way, 20 some posts later. Lol

  12. #25
    Join Date
    Jun 2001
    Location
    Michigan
    Posts
    12,077
    Your not seeing the obvious here. It would smack you upside the head if it could. I am not going to tell you the answer. I think I got a good hunch on whats going on.

    I am gonna help you think. Plus I plan on getting that manual scanned for you this weekend.

  13. #26
    Join Date
    Oct 2008
    Location
    Ohio, USA
    Posts
    168
    I work on some Tylers racks, I think from the 80s, and this sounds very similar to some of our setups. I have the Tyler book.

    As previously stated, the circuit on defrost sends hot gas out at a higher pressure than the rest of the HI-side, and it should come back to the liquid header as a liquid.

    This liquid header is also still at a higher pressure than the rest of the system (receiver).

    What I don't like about this system: How is a single 5/8" line full of liquid, supposed to supply 6+ OTHER 5/8" lines full of liquid??!

    If I'm understanding you correctly, this isn't an issue at the end of defrost with def term switches failing.... it's an issue during ALL of the defrost.
    Amazingly we haven't had a ton of issues with this. Although we do have an open case or two that are already iffy with temps, and when another case goes on defrost, these cases noticeably suffer.

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