404a high pressure?

[flyboy3b]

the box is 3/4" birch plywood with 1" foil covered foam insulation sandwiched in between. the doors are double glazed with a 1/2" space between.

make that double 3/4" plywood

[Gary]

the duct is basically 2 - 6" galvanized elbows going from the side of the box to the bottom of the evap chamber and it is insulated.

I would strongly recommend the insulated flexduct.

the evap chamber is 3/4" plywood with 1 1/2 " styrofoam on the top and right side (the left side borders the cooler) and 1" foil covered foam in the back. the bottom is just plywood.

The bottom and front should be insulated as well. Hot air rises up from the condensing unit.

anyhow,, i checked it this morning,, and it has started cooling again and im confused. i understand that the pressures are relative to the temperatures of the ambient air, air flow, and box temperatures. but,,,,

the ambient temps have been basically the same this whole time.

even when the box was warm, the txv would still frost up.

even though the superheat was really high the txv would still frost up.

through this whole thing,, the low side pressure had never been this high.

What I was seeing was essentially the same heat load being pumped by the condensing unit, but the evaporator load was much greater. In other words, the system was working about the same, but more heat load was entering, specifically in the return air. That return duct seems to be the achilles heel of this system.

anyhow,, here are the new readings,,,

ambient 76f
box 52f
suction line at bulb 42f
suction at compressor 51f
liquid line at receiver 97f
cond air in 77f... out 86f
evap air in 53f... out 44f
pressures at 60 and 270 psig
superheat 19f
subcooling 16f

You might want to open the TXV 1/2 turn. I would like to see the superheat back down around 12F.

[flyboy3b]

You might want to open the TXV 1/2 turn. I would like to see the superheat back down around 12F.

im not sure how long it had been cooling when i took those measurements,, ill check it again in a little while, now that its had a chance to cool down inside the box.

and yes,, there are adjustments i can make to tweak this cooler,, and i will. but im still miffed as to why the sudden change. as i said before,, the txv was warm. before that,, despite all the inefficiencies,, the txv would always frost up,, and the pressure (or temp) at the txv was never that high.

[Gary]

The increased heat load warms the refrigerant, increasing its pressure/temperature. The warm refrigerant (40F) is not going to frost anything.

We know the return has been a problem all along. Why did the return suddenly decide to leak more heat than previously? I don't know.

[flyboy3b]

The increased heat load warms the refrigerant, increasing its pressure/temperature. The warm refrigerant (40F) is not going to frost anything.

again,, pardon my stupidity,, but right at the txv,, the heat load doesnt exist yet. does it?

[Gary]

Actually, the refrigerant going through the TXV is warm liquid which quickly flashes off to bring its temperature down to the saturation temperature (40F). So at that point it is not yet down to 40F.

[flyboy3b]

but that liquid was no warmer yesterday,, than it was a week ago. wouldnt the liquid line have to be hotter to increase the pressure on the low side of the txv to where it was yesterday??

[flyboy3b]

heres the latest,,

suction line at bulb 58f
liquid line at receiver 93f
evap in 47f
evap out 39f
cond in 71f
cond out 85f
ambient 74f
pressures at 60 and 265 psig
superheat at 35f
subcooling at 17f
it seems like were losing ground here,, but ill check in the morning

[flyboy3b]

actually,, thinking about it,, im not sure how long it had been running for when i took those temps. it may have just started before i looked at it.

[Gary]

but that liquid was no warmer yesterday,, than it was a week ago. wouldnt the liquid line have to be hotter to increase the pressure on the low side of the txv to where it was yesterday??

The low side pressure/temperature is regulated by the temperature and volume of the air passing through the evaporator.

The low side temperature (and thus pressure) was warmer yesterday because the airflow entering the evaporator was warmer.

The warm liquid leaving the TXV must drop in temperature to match the low side temperature. It is not the cause of the low side temperature/pressure. The heat from the air is.

[Gary]

heres the latest,,

suction line at bulb 58f
liquid line at receiver 93f
evap in 47f
evap out 39f
cond in 71f
cond out 85f
ambient 74f
pressures at 60 and 265 psig
superheat at 35f
subcooling at 17f
it seems like were losing ground here,, but ill check in the morning

I don't think we're losing ground at all. The superheat is higher, but we know that the TXV orifice is oversized which will cause it to hunt, especially when it first starts.

We can open it another 1/2 turn and see how that does.

[Gary]

I would strongly recommend the insulated flexduct.

If you want to stick with the metal duct for the rigidity, you might seal it with duct tape and then insulate it with sheet Armaflex (closed cell foam).

An alternative would be several layers of Armaflex foam tape. Start at one end of the duct, spiral the tape around the duct, overlapping about halfway across the previous spiral, to the other end of the duct. Run the system for awhile. If the surface of the tape is cool to the touch, add another layer.

[flyboy3b]

If you want to stick with the metal duct for the rigidity, you might seal it with duct tape and then insulate it with sheet Armaflex (closed cell foam).

as is said before,, once i know the system is gonna be ok,, i will redo a few parts,, including teh evaporator chamber. i figure to eliminate that duct and just suspend the coil and draw air through it.

here are the latest readings,,,
ambient 74f
box 41f
suction line at bulb 34f
liquid line at bulb 97f
evap air in 45f out 36f
cond air in 77f out 89f
superheat 18f
subcooling 15f
pressures at 55/275 psig

lol,, this thing is bouncing around so much. if i can get a few steady readings,, im close,, i think

[Gary]

I would give it a layer of foam tape anyway, even if it's just temporary.

[Gary]

In your pictures, it looks like the duct "insulation" is a towel. I'm wondering if it got damp enough the other day to nullify it's insulating effect, then dried out and started working again.

[flyboy3b]

In your pictures, it looks like the duct "insulation" is a towel. I'm wondering if it got damp enough the other day to nullify it's insulating effect, then dried out and started working again.

there is insulation under that,, and no,, ive been trying to think of what happened when it warmed up,, but thats not it,,, everything was dry.

in my opinion,, in my vast experience,, i think the txv stuck open. it still provided enough resistance to keep the pressure under 100 psi, but not enough of a drop in pressure to provide cooling. all of the other factors seemed the same as any other day. it certainly got as warm,, if not warmer,, in the time we have been discussing that cooler. i can see no other significant differences that would cause that drastic of a change.

[Gary]

there is insulation under that,, and no,, ive been trying to think of what happened when it warmed up,, but thats not it,,, everything was dry.

in my opinion,, in my vast experience,, i think the txv stuck open. it still provided enough resistance to keep the pressure under 100 psi, but not enough of a drop in pressure to provide cooling. all of the other factors seemed the same as any other day. it certainly got as warm,, if not warmer,, in the time we have been discussing that cooler. i can see no other significant differences that would cause that drastic of a change.

I have no idea what heated the return air, but that is what caused the problem.

A stuck open TXV would have given us very low superheat and flooded the compressor. That didn't happen.

[flyboy3b]

this mornings readings are,,,

ambient 77f
box 43f
suction line at bulb 41f
liquid line at receiver 99f
cond air in 74f / out 90f
evap air in 52f / 41f
pressures at 60/275 psig
superheat 18f
subcooling 13f

well,, maybe itll happen again

[Gary]

this mornings readings are,,,

ambient 77f
box 43f
suction line at bulb 41f
liquid line at receiver 99f
cond air in 74f / out 90f
evap air in 52f / 41f
pressures at 60/275 psig
superheat 18f
subcooling 13f

well,, maybe itll happen again

Actually, the numbers are looking a little better. Try another half turn out on the TXV.

[Gary]

How is our wine cooler doing? Have we gotten the superheat down to 12F yet?

[nike123]

Maybe his vine is properly cooled now and he enjoy his vine finally.
That is what I will do if that is my case.

[flyboy3b]

How is our wine cooler doing? Have we gotten the superheat down to 12F yet?

sorry,, i just got busy. itll be a couple days before i can get back in there. but just from casual observations,, it seems to be doing ok.

[knight rider]

hi flyboy , if its doing ok , PLEASE DONT TOUCH !!!

[flyboy3b]

hi flyboy , if its doing ok , PLEASE DONT TOUCH !!!

lol,, advice well taken,, thanks

[thermo prince]

Whoaaaaa ? U mean this saga may come to an end ?

NO ! pls keep on toying with it , Flyboy !!

You've now got the " tamperitis" bug of fiddling with tx valves.

All us avid readers around the globe need our daily fix of this thread

Try and screw it up again so we can keep this project going .... if Gary was charging u for advice, it would have to go on record as the most expensive wine cooler in history!!!!

yuk yuk

regards
T-P

[flyboy3b]

hi honey,, im hoooome.
sorry guys,, ive been a little under the weather. anyhow,, these are the readings i took this morning,,,

ambient 74f
box 38f
cond air in 67f,, out 81f
evap air in 46f,, out 38f
liquid line at receiver 91f
suction line at bulb 40f
pressures at 50 and 255 psig
superheat 25f
subcooling 14f.

i opened the txv 2 turns and ill let it settle out and take the readings again in an hour or two.

Try and screw it up again so we can keep this project going ....

theres plenty of time for that T-P,,, i believe its a god given right for a man to make a fool of himself,, and i excersize that right often.

[Gary]

I assume the suction line is insulated between the coil and the bulb... and the bulb heavily insulated?

[flyboy3b]

i opened the txv 2 turns

let me rephrase that,, i opened the txv 2 quarter turns = 1/2 turn.

yes,, the valve and line are insulated

[Gary]

ambient 74f
box 38f
cond air in 67f,, out 81f
evap air in 46f,, out 38f
liquid line at receiver 91f
suction line at bulb 40f
pressures at 50 and 255 psig
superheat 25f
subcooling 14f.

Our superheat seems unwilling to cooperate. Is the TXV still hunting?

[Gary]

I wonder if the high side gauge is off a few psi, leading us to believe that the subcooling is higher than it actually is?

Connect the high side gauge to your refrigerant tank. The pressure should agree with the temperature of the tank.

[flyboy3b]

I wonder if the high side gauge is off a few psi, leading us to believe that the subcooling is higher than it actually is?

Connect the high side gauge to your refrigerant tank. The pressure should agree with the temperature of the tank.

to be honest,, taking the suction line reading seems very fickle. sometimes i have to take the reading several times before i get a reading that seems right (i take the lowest reading).

no,, the suction line temp is very stable (within a couple degrees). here are the latest readings,,,

evap air in 46f (in reality this is probably lower)
evap air out 38f
cond air in 67f,, out 83f
suction at bulb 36f
liquid line at receiver 91f
pressure at 58 and 250 psig
superheat 14f
subcooling 14f

give me a little bit and ill check the accuracy of my gauges (does it matter if the bottle of 404a is like 10 degrees or would it be more accurate if i warmed the bottle up?)

[Gary]

It would be better if the bottle were warmed up and stable. That way we can calibrate to a temp that is closer to what we use the gauge for.

[Gary]

superheat 14f

That's much better. We are very close to our target of 12F.

to be honest,, taking the suction line reading seems very fickle. sometimes i have to take the reading several times before i get a reading that seems right (i take the lowest reading).

The low side pressure/temperature is hunting because the TXV orifice is "A" instead of "AA". The orifice is oversized.

You are right to use the lowest readings.

[flyboy3b]

It would be better if the bottle were warmed up and stable. That way we can calibrate to a temp that is closer to what we use the gauge for.

i tried is with two gauges sets and the bottle of 404a was at about 35f. all 4 gauges were in the low to high 70sw psig. i have to remember to purge those gauges though, with the lossless fittings,, it doesnt seem to want to release the pressure as well.

ill check it again in a couple hours

[Gary]

Measure the temperature on the side of the bottle near the bottom. This is the temp that should agree with the gauges... and lose the lossless fittings.

At 35F, the gauge pressure should be 76 psi.

[flyboy3b]

and here is the last set for today,,,
evap air in 44f,, out 39f
cond air in 70f,, out 87f
liquid line at receiver 93f
suction line at bulb 37f
pressures at 60 and 250 psig
supheat 14f
subcooling 11f

[sptyagi]

hi i am sptyagi from india . i have ref system with r23 and 404 a cascade system . same problem i also faced in r23 system after repairing the fitting and recharging. at last we analysised there was some air was trapped into the system during charging. i suggest to take out complete the gas and was the system with nitrogen then vaccume it properly and charge the fress gas. hope you will get good results.