freezing evap coil

Paul S_3

What would cause a high subcool(35f)...and the Evap coil to freeze...this is a 5 ton split system r22 with txv....1 " 1/8 suction line.....5/8" iquid line.....line set over 120 feet.....condenser on roof air handler in basement....compressor amps below nameplate running at 12amps rated for 16 amps....another company was there two weeks ago....and I see a brand new head pressure control so the system had to be opened....non-condensables?...thank you Paul S

Techman

Not enough info

Temps. Pressure/Temps. That SH was at the comp? 120' straight up? Oil "P" traps in the suction line?

unclejohn

Non condensables

Is not the problem. Check for blocked dryer or bad TEV.

Paul S_3

frozen evap coil

there is a inverted trap at the condenser on the roof ...the refrigerant lines look like they go straight up...my high side was 230psi...liquid line temp 78f...low side was 55psi...compressor pulling 12amps rated for 16amps...i defrosted coil...evacuated to 250microns and recharged to 8f subcooling...and a 21f tempature split....i also purchased the txv(sweat type) already but didnt install it because all seemed good at the time i left...my partner called me and said they called back saying its not cooling again....when i go back im gonna check temp drop across LLD...but how do i verify that its the txv ....i want to be 100%.....and i could not pump down the system ....i closed liquid line valve and in a matter of seconds the internal relief valve was bypassing....thanks PAUL S

Techman

Freezing coil

The low side press is too low ,55psig is slightly lower than freezing. The TXV SH should be 10-12* , start with that ,its cheap. SH @ the comp? Where did you get the 8* SC  # from ? What is vertical separation? What kind of head press control? How did you defrost the evap coil? Lifting the comp internal relief valve? That's not a good thing !!!!! For those that don't mind "rule of thumb" . Most cond units can handle only 15-25' of LL, so you do the math! Room temp,  ambient temp??

Techman

Freezing coil

To go from 35* SC down to 8* SC, how many extra lbs. of 22 was stuffed into that system.? This system must have been charged to a full sight glass!!! LOL!

unclejohn

Your not

Gonna jam all that freon into the outdoor coil. If you replace the tev get the exzact one and just replace the guts and power head do not try and unsweat the valve big can of worms there. Also do your self a favor and but a refrigerant shut off valve in the liquid line at the evap. A pump down solinoid would be a good idea too. I can't belive you have a 100+ feet of liquid and you can't feed the coil are you sure ther is no blocked dryer.If there are no P traps every 10 feet in thr suction line then you may have a coil full of oil but then why is the compressor still running. Check the super heat at the coil, if not 10 - 15 open the valve if that won't get it replace the guts of the valve.

Paul S_3

if I can not put all

That refrigerant in the condenser coil...and I put a liquid line solenoid wouldn't that have the same effect? And what do you mean by traps every ten feet?...should there be traps every ten feet...?....when you say check superheat at coil...does that mean check the line temp at the outlet of evap coil and get my saturation temperature from my low side gauge on the roof at condenser? Or am I taking a pressure reading at the outlet of evap coil?....and what's the difference between superheat at condenser or at evap coil?....should they be the same? Why does it change? Thanks Paul S

Techman

freezing coil

If you use a LiquidLineSolenoidValve and you install the LLSV  just before the AirHandlerUnit then a "pump down" is easy. What is the vertical separation between the cond unit and the AHU ? That height difference might require the "p traps" . Checking the SH at the evap is for the SH of the evap only (10-12*) then every foot of suction line adds more SH ,13*-14*-25*-35* @the comp , then more SH is added from the motor in the comp and even more SH is added by the "heat of compression". The comp discharge line and the 1st couple of passes of the cond coil is for "desuperheating "only, not for  condensing. Having a press tap at the evap is rare so at the cond unit is the next best thing. I put in a "tap" on problem jobs. I believe most residential TXVs are a "one piece body" and do not have a replaceable "power assembly" so the entire TXV might have to be replaced and most res TXV do not have a "SH adjustment stem". Is there a SG/MI on this job? The low side press was below freezing (55psig) so a little while later , as the suction drops the (if) moisture in the Freon might freeze up in the TXV or the evap coil might frost/freeze over. Temps, press.!

Paul S_3

there is no sg-mi

In the system...the vertical separation I would have to say is about 85 to 90 feet....Paul S

Techman

freezing evap

 With that high of a height for the suction line there has to be oil traps to get the oil back to the comp , every 20' or so, I'll recheck that. That 5/8 LL is kinda big for a  5t unit w/ evap lower than the cond unit. And a SG/MI is a good thing. Why is the suction press so low?

Paul S_3

DIRTY

THE EVAPORATOR COIL WAS PLUGGED....THATS WHY THE SUCTION PRESSURE SO LOW....I REMOVED IT ,CHEMICALLY CLEANED AND HOSED IT DOWN AT SHOP.....PRESSURE READINGS NORMAL NOW....SUCTION PRESSURE WAS AROUND 80 PSI THIS MORNING (85F RETURN AIR).....BUT I CHECKED LINE SET (IN A PIPE CHASE)WHICH IS BRAND NEW REPLACED BY ANOTHER COMPANY TWO WEEKS AGO (THEY SAID IT WAS LEAKING).....THE ONLY TRAP IS AT THE CONDENSER....SHOULD I GO BACK AND INSTALL TRAPS AT EVERY FLOOR???....THANKS PAUL S

Techman

Evap coil

How many compressors has this system eaten ? If none than it would be a hard sell , your talking a couple grand for that job and no AC while your doing the job. You can actually look and verify that there are no oil traps ? IF none , then take a picture because you have a WOW .!!!!!!!!!!!!!!!!!!!! Why couldn't you wash the evap on the job?.