404a high pressure?

[flyboy3b]

hi honey, im hooome,

man,, we ended up driving back through that ice storm yesterday. it wasnt as bad in wisconsin as it was elsewhere, but it sure was slippery, and the snowflakes in milwaukee were 2" wide. crazy stuff.

so,, here is where we are today.
i moved the thermostat bulb to the inlet of the evap coil and adjusted the thermostat. these are the current readings (taken before i moved the thermostat)

ambient 74f
box temp 47f
cond air in 74f
cond air out 90f
evap air in 56f
evap air out 42f
suc after the evap coil 53f
suc at compressor 62f
liquid at receiver 98f
pressures 52/278 psig

ive included a couple of pictures (if they arent too large to post) so you can get an idea of what this thing looks like. if i could ask a favor,,, gary,,,, would you apply your magic formula to these measurements and post the results?

ok,, the pictures were too large,, so i posted them to my website,, and i will try to include the link here,,,
http://wavespub.com/cooler.html
lets hope this works,
thanks again
mike

[Gary]

ambient 74f
box temp 47f
cond air in 74f
cond air out 90f
evap air in 56f
evap air out 42f
suc after the evap coil 53f
suc at compressor 62f
liquid at receiver 98f
pressures 52/278 psig

52psi = 17F
278psi = 112F

112 - 74 = 38F TD. This shows a very heavy load OR non-condensables. I believe it is heavy load because the subcooling is not excessive (112 - 98 = 14F subcooling), but I could be wrong.

We can check for non-condensables by pumping down the unit and comparing the high side pressure to the temperature of the condenser.

Close (front seat) the receiver outlet valve. When the low side pressure reaches around zero psi, shut off the unit. Let it sit for about 15 minutes, then measure the temperature of the condenser. Insert your temperature probe between the fins near the center of the condenser.

We will need to know both the condenser temperature and the high side pressure.

BTW, do you have a pressure/temperature chart? They give them away at refrigeration supply houses everywhere.

Or here is an online chart:

http://www.parker.com/rs/PDFS/Ref_Temp_Chart.pdf

[flyboy3b]

ill do the pump-down thing tomorrow morning. i havent taken any temps down there,, but it looks like the box temp has dropped to the low 40s.

i would be surprized if there was any non-condensibles in there as i pulled it down to a 500 micron vacuum last time and the system itself has never run into a vacuum, but what the heck,,, it cant hurt to look.

and yes,, i grabbed a bunch of those little charts. handy little devils. i wonder if i can find a software for that to put on my cell phone?

[flyboy3b]

its me again,,,

i took these readings before i pumped it down,,,

amb 79f (this number can be misleading because at the time, both the ice machine and wine cooler were on. if you took the reading from the middle of the room,, it would be closer to 70f)
box temp 44f
evap in 52f
evap out 37f
cond in 70f
cond out 90f
suc line after evap 44
suc line before comp 56f
liq line at receiver 100f
pressures 45/280 psig

i closed off the receiver valve and it pumped the low side down to 0 psig in less than a minute. i shut the cooler off and waited for about 25 mins. at that time the temp in the cond coil was 66f and the pressure was 180psig. now i know what you might be thinking,,,,,, 66f would indicate a pressure of 138 psig for 404a,,, quite a difference from 180 psig. and im not saying that it would be impossible for there to be non condensibles in the system, but,,,,,, the temperature at the cond coil may be reading falsely wrong because when everything is off,, the adjacent (outside brick) wall would bring that temp down fast. the compressor was still warm (maybe 90f) so maybe the true temperature is somewhere in between those numbers. the low side pressure remained at 0 psig the whole time.

one question i would have is,,,,, if i somehow fractionated the refrigerant when i put it in,, how much of a pressure difference could i expect to see. i was unable to find a P/T chart for 143a or hfc 125 (the major components of 404a).

anyhow,,, thats where we are.
thanks,
mike

[Gary]

i closed off the receiver valve and it pumped the low side down to 0 psig in less than a minute. i shut the cooler off and waited for about 25 mins. at that time the temp in the cond coil was 66f and the pressure was 180psig. now i know what you might be thinking,,,,,, 66f would indicate a pressure of 138 psig for 404a,,, quite a difference from 180 psig. and im not saying that it would be impossible for there to be non condensibles in the system, but,,,,,, the temperature at the cond coil may be reading falsely wrong because when everything is off,, the adjacent (outside brick) wall would bring that temp down fast. the compressor was still warm (maybe 90f) so maybe the true temperature is somewhere in between those numbers. the low side pressure remained at 0 psig the whole time.

Another possibility is that your gauge is off by about 40psi, although that seems highly unlikely. Just to make sure, hook your gauge up to your refrigerant jug. The pressure should correspond to the temp of the jug.

Most likely you have air in the system and you will need to evacuate it again. Did you evacuate from both sides? Did it hold vacuum?

[Gary]

the temperature at the cond coil may be reading falsely wrong because when everything is off,, the adjacent (outside brick) wall would bring that temp down fast.

You might try placing a piece of cardboard between the condenser and the wall to block the cold air, then check temp and pressure.

Or better yet, measure the temp on the drip leg (the line between the condenser and the receiver).

[flyboy3b]

i dont actually recall if i pulled a vacuum from both sides or not, but its such a small system,, do you think it would matter?

i held the vacuum for about 10 minutes at 500 microns, i even tapped the side of the compressor,, just in case. but it is a new system,, and i have leak-checked it a couple of times. but like i said before,, the system has never run into a vacuum, so if it were leaking,, the pressure would be dropping (instead of sucking air).

my bottle of 404a is sitting outside, and its cold out,, but i should be able to check my guages with it. i have several other guages to try as well,, but these are the newest.

hendry, i appreciate your input. yes,, its an air cooled wine chiller and i agree,, i could use some more air across the condenser coil. at a point,, im going to have to live with a less-than-efficeint cooler, because that is the only location it can go (its a very small place). the txv, however, is a 1/4 ton, 404a txv. it should be plenty big for this small box.

anyhow,, ill post the latest results later tonight or tomorrow morning.
thanks again,
mike

[flyboy3b]

ok,, heres the deal,,,

it would appear that gary is much smarter than he looks (just kidding gary).
i checked my gauges against my bottle of 404a i brought in from outside. it is 26f and my high side gauge read 150 psi. well,, thats not right. so i checked the low side gauge and it read 65 psi. that sounds more like it.

i purged the gauge set and retook the readings and both sides measured about the same (correct) pressure .

i double checked this against my bottle of 134a and both sides measured correctly

what do i gather from this? is the lossless fitting not letting the gas back out of the high side fitting? is there something in the high side of the gauge set thats not letting the pressure equalize? is this normal for a REFCO set of gauges or are they broke. this wine cooler is the only system ive worked on in the last week,, so i had no reason to purge the gauge set each time i used it. and why does the low side equalize properly each time? the fittings are the same and they are all brand new.

thanks again gary for your sage and intuitive advice.
mike

ps,, i will retake the readings tomorrow when the restaurant is closed

[hendry]

i dont actually recall if i pulled a vacuum from both sides or not, but its such a small system,, do you think it would matter?

i held the vacuum for about 10 minutes at 500 microns, i even tapped the side of the compressor,, just in case. but it is a new system,, and i have leak-checked it a couple of times. but like i said before,, the system has never run into a vacuum, so if it were leaking,, the pressure would be dropping (instead of sucking air).

my bottle of 404a is sitting outside, and its cold out,, but i should be able to check my guages with it. i have several other guages to try as well,, but these are the newest.

hendry, i appreciate your input. yes,, its an air cooled wine chiller and i agree,, i could use some more air across the condenser coil. at a point,, im going to have to live with a less-than-efficeint cooler, because that is the only location it can go (its a very small place). the txv, however, is a 1/4 ton, 404a txv. it should be plenty big for this small box.

anyhow,, ill post the latest results later tonight or tomorrow morning.
thanks again,
mike

[QUOTE][/QUOTE

thank you to you, too!

you know ... you could modify the condenser to be more efficient with current constraints.

i've done it for my clients.

it became a hybrid condenser. you know what?
lesser condensing pressure/temp & better performance.

worth trying if you are in for better system.