[Reeferman]

Bryan I don't work on these systems but after hearing what you said that night and hearing what Garth said about it I think he was right about how to fix this problem.

 

[icemeister]

Bryan....

That was a lot of good info. Now I'm seeing things in a better light.

I had made an assumption that there was no way that the subcooled liquid from the supply line could flow into the saturated return line and then into the discharge line ahead of the condenser because it was obvious to me, on paper at least, that the pressure at the condenser inlet had to be higher than the subcooled supply pressure. Since you have observed flow must in fact be a pressure difference......but how and where is it occurring? I dunno, but with the installation of the solenoid valve in the LR line however, it becomes moot point.

We are not over charged since we have problems with liquid supply in the higher amb days. we get higher head but no subcooling. If it was a overcharge our subcooling would be higher. The receiver is setup to fill if our disch rises above 175psi and our subcooling is over 15. This is what dumps the excess charge into the receiver.

Is this receiver fill control logic 175# and 15F LSC or is it and/or? Is this a slow, metered dump? What condition(s) empties the receiver? What's your design condenser TD and what TD are you actually seeing during these high head problem times? I'm assuming the condensing temp is higher than design then as well?

 

[bryan l]

the history is good and bad depending on the stores. We have over 21 of these racks in opperation around here. They are all suffering from this problem. Some stores more than others. Some of the installs could be questionable but not all. Non-Cond is a possability (always is).

The receiver is charged by 175# AND +15degree SC. Just a half inch line dumping in. Pump out is based on suction pressure. If it goes 15psi over the SP it will de-energize the pumpout. (pumpout is through a TX, Heat Ex on the liquid return line and then dumping into the suction header. It is never off really)

 

[gerryboy00]

My issue is when NOT in defrost the liquid is still dumping into the cond supply.

In order to have liquid or gas flow you need a pressure differental. This is basic. now why are we getting this diff between the return line and condenser.
what was the pressure diff. you read???did you closed the valve on the liquid return line manually and read a raise in pressure compare to disc. line???

-Is it due to the pressure drop across the discharge check valve?(that is only in our full time circuit, the other 2 condensers dont have these)
I dont think so

-Is it the slight increase in pressure the return line gets by aborbing heat from the compressor room, boiling off some liq and the pressure rises just enough to dump some gas into the disc line?
interesting avenue,
is the liq. line subcooled at 40° as show in the skecht?
can it raise in temp somewhere in the store too??




-Is it some vacuum effect at the tee where the two lines come together? Liquid is flashing off as it comes in contact with the disc gas and or hot piping, thus producing a flash point that draws liquid in more and more. Thus causing the flow?
dunno but heh anything can happen

 

[gerryboy00]

The receiver is charged by 175# AND +15degree SC. Just a half inch line dumping in.

after the dumping from 175 to 155, the return line stays at high pressure due to the location of the check valve on those line but at that moment the disc. is lower isn't it?

 

[Dowadudda]

I also want to know what your actual TD is during this high head pressure situation.

TD measurment can get us pretty focused pretty quick.

I am leaning so much torwards charge and manipulation as she shifts. I can not begin to tell you, how many guys who first get on our enviroguards that mistake it's operation and go to fiddling with setpoints or misdiagnosing, me being on of them until I finaly understood how she works.

Have you verfied, authenticated the actual way the control is measuring the subcooling so that it is indeed dumping when we want it to?

You made a mention of when charging gas that your seeing flash in sight glass. I can't remember what it was you said but. You know guys get messed up on charge easily enough when you have a HGDF system, let alone you have the arrangement you have on top of this. I'd say you need to have everything refrigerating, nothing defrosting, on goo design load day, and see what she does. TD on condenser, ratio, receiver level.

I think either your charge is messed up, non condensibles or your not dumping correctly to receiver.

Now the last option I have is not to insult you or anyone, but I have seen 30 year experienced men totally miss this. Heck, I have missed it. Is the condenser fully cleaned. Not brushed down, where the fins appear clean. But rather, there is no impacted debris, cotton wood or what ever in the middle of this condenser. TD would tell you in a second. Some guys will swear up and down, and then you work to get the deep impacted stuff out and you have yourself a whole new rack.

I have seen condensers, 26 fans, look pristinely clean, standing underneath them, with a flashlight. But that cottonwood is so impacted into it, you simply don't see it.