low temp split

Paul S_3

hey everyone.... I have a job in NYC that has been giving us a problem for a long time its a split 410 a system. with the condenser and air handler side by side condenser discharge in and take are ducted I have a high side pressure of 400 psi and a low side pressure of 135 psi my super heat is 2 degrees and subcooling 16 degrees the problem is the low-temperature split which is 12 degrees I am pretty stuck on this job and don't know where to go from here the customer says that this is always been a problem... thank you Paul S

Techman

low temp split

For a sec I thought you were talking about a  freezer. Are you sure about your numbers? 2* of SH? plugged evap? and why in the world do you have 16* of SC when you need only 2-3-4-5* with the evap and cond side by side?!?! And what does 12* of "lo temp split" mean? And what is the ambient to go along w/ that 400psig head? And what is the air temp of the air going INTO the cond coil?And the cond air is ducted? Got a picture? And what is the indoor temp to go w/ that 135psi lo side press?

Paul S_3

low temp split

the temp split i mean is the TD across the evaporator coil is 12f....85f return and 73f supply...the evaporator coil isnt plugged either is condenser(from what i can see at condenser)the intake and discharge of the condenser are ducted to the outside(front of store)intake today was 92f and discharge was `127f...my superheat reading was 2f....and subcooling was actually 6f not 16f sorry....the indoor temp of the store is 85f...and its been really hot here in NYC the last few days up near 100f....the problem is the low TD across the evaporator coil....at first i thought it needed refrigerant until i took pressure /temp readings.....could it be moving too much air.....blower motor is a 3phase belt driven motor....thanks PAUL S

RJ_4

t.d.

Ducted condenser coils almost always cause above normal. press./temps.especially if they were added to the original install and are almost always dirty unless signs of cleaning are evident.  I would recommend getting in and washing out the cond. coil with cal clean for a start, than looking at air flow issues.  you may have to cut some access holes, always wash out coils starting from the side opposite the air flow. that low superheat reading sounds strange with your other readings,  how are you measuring it.

Paul S_3

low temp split

i am taking a temp reading from the suction line near compressor.....and subtracting the sat. temp on the low side gauge from that line temp....thats how im getting my supperheat reading.....there is a condenser and air handler hung in drop ceiling side by side with about 4-5 feet of refrigerant piping connecting the two units...i believe the make is "united air cool corp" if im not mistaken ....   PAUL S

JStar

AC

Can you extend the lineset to get about 20 feet of it between the units?



What was your indoor dry bulb and wet bulb?

Paul S_3

low temp split

my indoor dry bulb was 84f....i didnt have my psychrometer to check my wet bulb ...therefore i really didnt know my target supoerheat i will go back monday...i actually do have the room to have 20 or so feet of line set coiled up....if you think that would help.....thanks PAUL S

Techman

temp split

That SH of 2* is dead wrong, the TXV/evap should have 10-12* BY ITSELF ! Is the TXV SH adjustable? Is the TXV bulb secured in place? What tonnage? What kind of store?. Is your gauge on 0psig when opened to the atmosphere? Check w/ the mfrg about minimum line length !

RJ_4

split

You might want to do the detective work,   make sure the units are the right size for the heat load in the bldg and are installed correctly before you spend to many unbillable hrs on the job, than get I.O.M.s and fan curves for units.

Paul S_3

low temp split

okay I will do that tomorrow morning..... but wouldn't a TD across the evaporator coil be the same if it was under size? also if it was moving too much air could this be the problem? and are there any tests I can do to determine the fan speed? thanks Paul S

RJ_4

split

get all unit info 1rst    a fan curve will help you determine air flow, chances are the cond unit also has ajustable air flow data available, you will need a good tachometer.

unclejohn

Are You

Sure your not recirculating your condenser discharge into your in take. Is the discharge above or below the intake. If your DT is low you need to open the TEV or check for proper air flow. Too much air lowers DT.