Where are you reading the superheat temp at?

 

at the service valve on the condenser

 

Can't you take SH reading at outlet of evaporator?

Sub-cool reading on outlet of condenser?

Reading your original post seems like your readings are reversed.

Perhaps I am confused.

 

taking the sh at the outlet of the evap would require me to pump down the unit to install a service port, there isnt one on the evap currently. the sc reading i gave is at the outlet of the condenser. what about my readings seems off? i double checked what i wrote and everything seems right?

 

you don't need the pressure at the evap to get the evaporator superheat. The pressure at the condenser service port will suffice. You only need the line temp at the evap. That being said, it probably won't tell you much except how much heat you're picking up through your line set. Your suction pressure is low and your super heat seems a bit high, assuming that your airflow is correct (750 you stated) then you are starved in your evap. The condenser side looks okay but without a charging chart, it is hard to say. You could check your evap superheat to see if you are maintaining a better superheat at the outlet than at the condenser but you are still under 32 with your saturation temp so you need to increase pressure in the evap either by increased airflow or adding additional refrigerant. Do you not have a chart which tells you what the subcool value should be for a given set of load conditions? If you are adding and finding that the superheat is continuing to come down, then that basically indicates that the TXV would be happy to introduce more refrigerant to the evaporator, if it only had it. You may also want to check your TXV bulb installation. Squeezing the bulb or strapping it to a drop light to see if your TXV opens...

 

i can however do that if needed so i can check the superheat at the evap outlet

 

i will check the line temp on the outlet of the evap and compare the 2. as far as the subcooling chart for the condenser i am basically right on the money with my discharge pressure given my discharge line temp and adding 5 psi to allow for the long length and rise of the line set which is states to do.

 

your airflow is reduced from the required 800 cfm to 750 which is about a 7% variance. Expect your subcool to be slightly higher than the chart indicates, with the correct charge, since you are using a TXV and and have reduced airflow, the txv will throttle down and increase your head pressure and subcool values slightly.

 

Without a mini vane is there a formuma to use to fibd cfm

 

i have around a 45 degree line temp at the outlet of the evap. so thats puts me at around 17 degrees of superheat. i did trace out the line set and found that theres about 15 feet that runs through a boiler room that stays at a constant of at least 110 degrees plus. txv is secure and insulated tightly.

 

That SH reading is much better than the 23* earlier.

now if you can get it down between 8-12 * .

seems like low charge

what's refrigerant capacity on name plate? figure in for the 60 feet line set.

Are you weighing in the charge? or just charging by SH/SC?

 

i weighed in the factory charge of 5lbs 2 oz, i did not factor in the extra 45 feet of line set cuz i figured i could get it close with sh/sc. i stopped keeping track at 6lbs 2 ozs. if i had to guess i prolly have around 7lbs in it now total. batteries died on my scale that day. so if i could get my sh down to 8-12 at the evap you would call that close enough?

 

8-12* superheat would be what you want to shoot for. higher the superheat, the more starved the evaporator is. you definitely have to factor in them long linesets

if you can get the superheat down to the margin, roll with it.
you will know your overcharged if your superheat falls below the margin.
too low of superheat would allow liquid to flood your compressor, you don't want that to happen.
after that check your sub-cooling, even if its 15*+ run it.
superheat is most important, proper superheat protects your compressor.

 

ok on monday ill continue to add and hopefully itll continue to come down. ill report back once i do. thanks for your help so far

 

Add slowly and don't slug the compressor. Basically throttle it. Small bits at a time. Let stabilize and recheck superheat before adding more.

Actually I forgot. You don't have service valve on low side.

My bad

Good luck, looking forward to hearing if its working right

 

You said you replaced the compressor once before , by chance did you add a trap to help get the oil back to the new compressor. also I would look at increasing your blower speed, not knowing the lay duct layout, adding a small grill on the ductwork or plenum to get you between 800-1000 cfm.

 

haha . i get paid by the hour so ill put it in as a vapor no prob. ill definatley keep you updated. have a good weekend sir. also no to answer your question i did not think to add a oil trap, where would be a good location in the future to add one, i have 3 units with the same line set runs and location i may do that one day. i only have access to about 15 feet in the attic and around 10 feet before the condenser outside? im thinkn neither of those places would be a good option?

 

What was the outdoor air temp when you took your readings?

 

68-70 today was the oat

 

I'm not a Trane guru, but isn't that a 2 ton ahu on a 2 1/2 ton condenser? And you replaced the txv with a 2 1/2 ton expansion valve, what tonnage was the original?

 

there both 024s so if im reading the model numbers right which i should be there both 2 tons

 

I wouldn't add more gas stacking up more subcooling will not solve the issue. Some expasion valves are adjustable. If that one is I suggest tryingthat first. Also check bulb location if liquid is splashing on the pipe where the bulb is mounted it could cause the valve to close more than it should. The answer is somewhere in the metering or a restriction in the liquid line.

 

I agree. If there is 14 subcooling, there is certainly enough refrigerant in there.

Take liquid line temp at indoor coil directly before txv. Better yet, temporarily install a piercing valve there to check the pressure drop of the liquid line. You will have to pump down to repair the restriction and can remove the piercing valve then.

 

Or you have air in the system.

 

This txv is not adjustable, and even if it was where its located its definately not easily accessible. I have tried moving the bulb in different locations but nothing changed. I serious doubt its air because i did a full evacuation, vacuumed to below 500 microns, and weighed in new 22 and it has a new LL dryer. All of the LL that i can see looks to be in good shape, no kinks, and unless its in the LL in the wall somewhere I will never know.

 

What doesnt make sense is why originally before the txv change i had 1-2 degrees superheat and now i have 23?

 

I've had bad txv's out of the box on several occasions. It really stinks.

 

I've seen driers loose their beads and clog a liquid line in a elbow easy to check if you have a temperature drop between the condenser and evap then you probably have a restriction. Some expansions don't work but thats often not the case. Could also have hardened arteries aka sludge in the coild feeder tubes.

 

I will install a piercing valve before the txv, and check for a pressure drop. Is any to be expected if there is no restriction but because of the length and lift? How much of a drop would be a good indication of a restriction?