404a high pressure?

[flyboy3b]

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?

[Chicharronne]

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.

[flyboy3b]

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

[Gary]

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.

Right now it is working reasonably well despite being grossly undercharged with a maladjusted TXV. Once we get this thing working right, you will be able to set the temp wherever you want and it will hold no matter how often people are in and out of it. The TXV will give you very fast recovery. That's what a TXV does best.

[flyboy3b]

well,,, there is trouble in paradise.

the system has a small leak,, and im not sure where it is. ive leak tested everything accessible and no luck. itll probably be monday before i can get at the 2 coils.

when i went to adjust the subcooling i noticed the box temp had climbed to 52f, so i checked it over and decided to just pump it down and start over. after evacuating the system i hooked up my vacuum pump and started pumping it down. the vacuum gauge hovered between 400 and 700 microns. when i disconnected the hose going to the cooler,, it promptly came down to 200 microns and when i hooked it back up,, it jumped back to 700 microns. so that rules out the hoses, fittings, vacuum gauge and vacuum pump.
anyhow,, i hope its in the evaporator,,, its much more accessible.

on a different matter,, i asked this question on another thread,, but im still not exactly clear on this,,,
with a standard recovery tank with a liquid port and vapor port,, does the liquid port reach into the bottom of the tank? in other words,, if i want to get liquid to come out,, do i leave the bottle upright and use the liquid port,, or do i invert the bottle and use the liquid port.
sorry if this is a stupid question,, but ive never seen the insde of one of those tanks.

[Gary]

well,,, there is trouble in paradise.

the system has a small leak,, and im not sure where it is. ive leak tested everything accessible and no luck. itll probably be monday before i can get at the 2 coils.

when i went to adjust the subcooling i noticed the box temp had climbed to 52f, so i checked it over and decided to just pump it down and start over. after evacuating the system i hooked up my vacuum pump and started pumping it down. the vacuum gauge hovered between 400 and 700 microns. when i disconnected the hose going to the cooler,, it promptly came down to 200 microns and when i hooked it back up,, it jumped back to 700 microns.

That doesn't mean you have a leak. It means you didn't leave the pump on long enough. Refrigerant is absorbed into the oil in the compressor. When you shut it down, some of that refrigerant escaped from the oil and brought up the pressure. The question is, after it came up to 700 microns, did it stay there or did it continue to rise? A leak doesn't stop rising until it reaches zero psi.

on a different matter,, i asked this question on another thread,, but im still not exactly clear on this,,,
with a standard recovery tank with a liquid port and vapor port,, does the liquid port reach into the bottom of the tank? in other words,, if i want to get liquid to come out,, do i leave the bottle upright and use the liquid port...

Yes.

[flyboy3b]

gary,, i had considered that,,, or the possibility of moisture in the system, but this system is so small. i figured it would have balanced out over a period of 20 or 30 minutes. also considering the rise in box temp (which it had been holding fairly well) and the drop in pressure. it just seems the most likely answer.

monday,, possibly sooner,, i will retake the reading and see where we are at

[Gary]

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

when i took these readings the pressures in the system were 55/200

55 = 19F
200 = 89F

Well... that changes everything... and it explains everything.

89 - 68 = 21F TD

Light load... and we can forget about non-condensables.

52 - 19 = 33F superheat

89 - 91 = -2F subcooling

You have low subcooling (not enough refrigerant in the high side) with high superheat (not enough refrigerant in the low side). That combination tells us the system is undercharged. Add refrigerant until the subcooling is 10-15F. Then we will see some very different readings. It helps to have accurate gauges.

[flyboy3b]

lol

ill try to check the subcooling this aft,, otherwise in the am