In truth, the average tech takes very few readings and wouldn't know what those readings mean anyway. They fix the obvious problems and never tune the system. If/when it puts out cold air, they take the money and run.
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here is the latest set of measurements,, and i went out of my way to verify them,,,, and for what its worth,, its seems like its doing ok.
box temp 44f
evap air in 55f (still seems high to me)
evap air out 44f (it seems like that should be a little lower as well)
cond air in 65f
cond air out 90f
liq line at receiver 98f
suc line after coil 48f
suc line at comp 63f
pressures at 55 and 280 psig
looking back at my other measurements,, the suction line temp didnt change much after that txv adjustment, in fact,, none of the temps changed much. the txv is still icing up but not excessively. the system is run by a line voltage thermostat (right now i have the bulb a little too close to the evap coil so it turns on and off about every 25 min mins depending on usage).
anyhow,, i have to run out by my brothers house and help him install a snowblower to his john deere and ill check back a little later to see if anybody wants to throw their two cents in.
thanks again,
mike
I would place the thermostat bulb near the return air duct. That alone should make a big difference.
Set the thermostat to 35F. Let's see what the system does in a "normal" temperature range.
I'm assuming the evaporator fan runs non-stop... even during the off cycle? If it doesn't, it should.
Actually, the numbers look a little better this morning.
Actually, it makes more sense... and this is the temperature that the thermostat bulb should be sensing and controlling.
Not if the air in is 55F.
Hmmmm... here is a new temperature measurement for you to take: Locate the copper return bends along the side of the condenser. Read the temperature of the center return bend.
Also, measure the temperature of the liquid line near the TXV.
man o man,, talk about cold and wet. it took us 2 hours to hook up this blower. have you ever looked at the underside of a john deere tractor with a snowblower on it? theres a belt thats about 10 feet long that serpentines through all these pulleys, a bunch of cotter pins and some strange looking arms with pins and holes.
the problem is that neither of us have ever seen it installed and we dont have a manual. anyhow,, all is well,, and the snow is gone.
back to reality,,, gary,,, i bought the thermostat from american scientific (like an army surplus for electronics) for 5 bucks. its a ranco controller and i think it was designed for high temp applications. so i opened it up and adjusted the contacts to close at around 35f giving me about a 10 degree differential. the problem is that i think when i adjusted beyond the design range of the switch,, it through off the sensitivity of the switch. as i move the switch further away from the evap coil,, it takes exponentially longer for it to shut off, causing ice build up on the coil. but yes,, i agree,, it needs to move further away. once everything else is up to snuff,, i will start playing with that.
i will try to get back into the cooler this afternoon. it takes a little time because i have to disassemble the shelves on the cabinet to the right, but we can try another full turn ccw and see what happens.
in the meantime,, im gonna dry out my shoes and try to warm up a bit. there was something else i was gonna say,, but i forgot what it was.
thanks ,
mike
i just remembered what it was,,,
i can take those temps on the loops, but i have to take a cover plate off to do it and it will read high because of the ambient air entering the evap coil. but the readings should be relative to how much refrigerant is in the coil, sort of.
Let's cancel the TXV adjustment for now. And the loop measurement I want is on the condenser coil, not the evaporator coil.
Thinking about your surplus thermostat with the 10F differential and just shaking my head. You need a real thermostat... and about a 3F differential.
When you say "near the coil", please tell me you have it sensing coil inlet temperature and not coil outlet temperature.
hey,, i paid 5 dollars for that thermostat, lol. actually,, i do have some other thermostats i can use,, its just that they were designed for switching 25 amps,, and id rather save them for other projects i have. the way its set up now,, it cycles on for a bout 5 or 6 mins,, and shuts off for about 15 to 20 mins.
getting readings off the condensor might be a little harder (its tucked back in there pretty good,, but i will try
yes,, the evap fan runs all the time,, its my only protection against freeze up.
no,, if i moved the sensing bulb for the thermostat to the return air for the evaporator,, i would have to readjust the contacts back close at a higher temp.
and no,, the john deere is a not like a big tractor,, more like a big lawn mower.
and ive seen alot of bull as well,, but probably not the kind that you mean
Hmmmm... I'm trying to get a mental picture of this system. Apparently you installed an oversized condensing unit. Assuming the airflow is pull through, and we know the airflow exits the front, then the condenser coil must be sticking out the back. And you have it buried in the wall?... so it's getting restricted airflow, but the air is really cold because it is winter. Does that about describe it?
Please tell me I'm wrong and the condenser is not inside the wall.
hi Sir flyboy3b,your thread looks interesting and educational i had a great time reading and thanks to Sir gary for such overwhelming exchanging of professional ideas i may say
i am working here in the middle east where ambient temp varies from time to time especially now a days,where it is getting colder,but not as colder than in US,
as young compare to you guys ,LOL,i just encouraged myself to ask question about your thread's query
your Box temp=43f is desirable to you as application call's for it ,in these temp what really problem's you Sir,i mean is/are other components of the system affected,i mean those visible undesirable symptoms like frosting.
thank you very much
the reason for asking is that,it seems your desired room temp is quitely near to the point u wanted but
still problems you
hope your scrap designed system will soon works well.
Okay... here's where we are at this point:
The thermostat sensing bulb should be sensing the return air.
The condenser should be at least 3 inches from the wall. If this means you have to move the ice machine, then move the ice machine.
The unit isn't running long enough to get good readings, apparently because you are concerned about frosting the coil.
The suction pressures are going to run low and the coil is going to frost, because the condensing unit is oversized. Not to worry, it will melt during the off cycle.
Place a glass of water in the middle of the box and stick a thermometer in it. This will tell you the actual product temperature and then you can ignore the box temperature, which seems to be close to the evap air out temp for some reason.
Are we making any progress this morning?
BTW, I can understand saving money by doing the job yourself. What I can't understand is using junk parts, which are not even designed for this type of system, from the surplus store. Get a real thermostat.
There is a time to be tight and a time to be right.
I Am Sure That The Unit Tev Is Too Small And There Is Far Too Much Gas In That System.
Check The Sub-cooling And Check The Superheat!change The System To Cap Tube!!!
325 Psi At 70f.you Will Murder That Compressor If That Ambient Temp Goes Up!too Much Gas Backing Up In The Condenser.
it looks like i wont be able to get those readings till tues or wed. me and my girlfriend are heading out for a couple days,, just to get out of town,, maybe sit in a hot tub for a while,, have a nice dinner or two,, and try to warm up.
the condenser is 2" from the wall, and i also opened up the wall to give it some extra space and yes,, the condensing unit is oversized, but at the time i needed to get it running and thats all i had on hand to get it working. at some point when i have more time,, i will reinstall the old system with a cap tube.
remember,, i have never built a system from scratch before,, so i just went with what i knew (or thought i knew) and it has been a good learning experience for me.
as far as the thermostat goes,, its not a "cheap" thermostat,, i just didnt pay alot of money for it. its a ranco thermostat and it is adjustable. give me a few days and ill go in and move the sensor bulb and adjust the differential down.
markacs,, the txv is a 1/4 ton and it should be plenty big for a little box like this,, but i agree,, it should be a cap tube system. it started out as a cap tube systm.
thanks for all the input,, ill see you folks in a few days,
mike
I'm sorry but as 404a is a blend of refrigerants you cannot charge to a full sight glass, due to the fact that some vapor is always going to be present. This is quoted from Althouse. Turnquist, et. al., and also known from experience.
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
Wait until the evap air in is 40F or less, then take measurements. If the unit shuts off before the evap air in gets below 40F, then the thermostat isn't set low enough.
BTW, I don't think you could pick a worse location for that condenser. Judging by the picture, its a wonder that it gets any airflow at all.
i dont think the evaporater return air will ever get that low,, but what the heck,, i have time. maybe next monday when no one is going in there.
and yes,, i agree,, the condenser coil is in a bad place,, but ill make sure it gets the air it needs. the restaurant is very small and there is no basement. you would be shaking your head even more if you knew where all my remote condensing units were and how i keep them cool.
I take it the thermostat is located inside the box? The thermostat can be located anywhere that's convenient, as long as its sensing bulb is located in the return air. For example, you might want to locate it in the machine compartment on the outside of the evap cover plate.
I've been shaking my head for forty years. Nothing surprises me anymore. Let me guess: They are in a crawl space under the building, sitting in the mud... or maybe up in the attic, roasting in the summer and getting a hernia from the head pressure. Been there, done that.
You might consider turning the entire condensing unit 180 degrees. Room air would enter the condenser from the bottom of the opening and the heated air would then rise and exit out the top of the opening back out into the room.
I hope you aren't planning to put a door on that opening. You would have the hot air recirculating.
if you look closely at picture of the right side,, you will see and electrical box with some yellow wirenuts sticking out. along the edge of that junction box, in the middle, you will see a brass knob. that is the thermostat.
all the pipe connections are on that end of the condensing unit,, turning it around would be a real nightmare to install or repair, but its a nice idea.
ideally,, i would have one or two remote units in the basement, and just pipe everything from there,, but its not possible
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
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?
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
flyboy3b
1]your design is aircooled chiller.
2]insufficient subcooling @ condenser.
3]wrongly select xpansion valve
if you look into the above you'll have better cooler box.
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?
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
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
[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.
here we are again,, and here are the current readings.
ambient 75f
box temp 39f
evap air in 50f
evap air out 41f
cond air in 68
cond air out 81f
suction line at txv 52f
suction line at comp 68f
liquid line at receiver 91f
i closed the receiver valve and pumped down the system and the temp at the condenser was 80f and pressure was 190 psig which is about 15 lbs high,, but that may have balanced out had i waited a bit longer.
when i took these readings the pressures in the system were 55/200 and i suspect a small leak. i leaked checked it again and found no leaks,, but i have not checked either of the coils. next monday
i will recheck the pressures and leak test the other parts if needed. in the meantime,, i topped it off with a couple of ounces of 404a.
hendry,, what modifications are you reccomending?
I do a mostly reataurants and if you're chilling fancy wines then the mean temp is around the low 50's. I've done several cases that have heater to bring the temp up.
as for 404a, I used to do a lot of Wendy's. they used hobart reach in freezers for french fries. My job was to go behind the other guys reluctantly doing food service(HVAC guys who thought they were too good) I had a unit this guy worked on that had 2 9' cap tubes he replaced then walked away without checking. unit running low pressures. I pressurized to 125psig with nitro and leak checke. pressure held the entire time. weight the charge in and still low pressure. called the factory about the caps. they were correct. factory tech said if the unit was in an area with an ambient temp higher than 78 then the oil seperates from the refrige and coats the inside of the evap. the unit was next to the fryers. I added a couple ozs and temp dropped. they make a flush I have used on other fry freezers since.
i am aware of the oil problem,, i dont think the temp has been high enough for that to happen,, plus the fact that it is a new system. but i will keep it in mind as a possible problem. i keep the temp down in the wine cooler partly because people are in and out of it all day and the temp rises fast.
thanks,
mike