Another frozen walk in...

[sandpipertech]

What do you guys think? Equipment info below:
(I think it was Bohn equipment)
Evap - ba82p-a-sia-tsm2a1/050205276
Cond - beha008h2-hs2a-b/050207420
No outdoor fan cycling control. No defrost timer.

Arrived after 1st call, different tech (evap frozen up...bottom 1/2 of coil)
On this 2nd call found same prblem. Bottom 1/3 of coil frozen. Drain line clear.
THawed out ENTIRE coil. No ice left except on the sides on the return bends. FIred up back up...Superheat after 15 minutes of run time @30 deg F.
Adjusted valve out 1 full turn. Super heat after 15 minutes down to 18 deg F...
Went down and backed out valve 1/2 turn...superheat back up to 27-30deg F, but every 5 minutes the superheat would drop like a rock down to 13 degrees then right back up in the upper 20's. Let run for 15 min, no change. ....now frustrated. Backed valve out 2 turns and superheat immediately dropped to around 10-13 deg F. Let run for 30 minutes and superheat never changed from that. (This was all done with box running around design temp of 32 deg F.

Now, i noticed after all this that a very very light frost was forming on the bottom 1/3 of the coil on the return side...all the distributor caps are frosted. (Box down around 30-32 now and about satisfied).
I think, and hope, that ive solved the icing issue by adjusting the TXV (although the TXV may on the way out and need to be replaced soon).
Current outdoor ambient is at 65 deg F.
R-22 system.
Low side psi 40.
High side psi 190 ( if i remember correctly).
Sight glass full of liquid.

Do you think I might have nailed it with the TXV adj. or is that bottom 1/3 frosting suspicious? If so...any ideas?

THanks guys...

[ZeroTolerance]

Condensor fans operating at correct amperages? Low charge? Restricted TXV or Filter drier, faulty thermostat? I am assuming bad TXV

[tjc76]

I would drop the superheat a little more, try around eight degrees. Does this unit have a headmaster?

I am still trying to fathom how you are running this box to 32 degrees with nothing but off cycle defrost- maybe the problem is that the bottom of the coil can't get warm enough on the off cycle to clear the frost.

Is this a pumpdown system, or does it drop out?

[ZeroTolerance]

Oh... Didn't read no defrost timer. Interesting

[jason_duren]

i have had same problem before replaced t-stat to start. after that was still getting same thing froze 1/3 to 1/2 way up. replaced txv havent been back except for normal service. problem happened about 2 years ago. owner called today and walk-in froze again. have to go tommrow and ckeck it.

[sandpipertech]

I would drop the superheat a little more, try around eight degrees. Does this unit have a headmaster?

I am still trying to fathom how you are running this box to 32 degrees with nothing but off cycle defrost- maybe the problem is that the bottom of the coil can't get warm enough on the off cycle to clear the frost.

Is this a pumpdown system, or does it drop out?

Yea, thought that was kind of odd also...but...box has been running for 6 years like that.
Pump down system.

[monkeyman#1]

How often are they in and out of this box?

[skpkey9]

Theres more to this story...

Also sounds like you are oil logging in the evap need to force it back into condenser and you also need some kind of low ambient controls on this unit and absolutly need to be on pumpdown set up with defrost timer...

[skpkey9]

Also depending what is kept in this box , I'd get the box close to temp and shoot for 10* sh at evap and make sure you are no less than 20* SH and NO more than 40* SH at condenser....

Hope this helps...

[jason_duren]

How often are they in and out of this box?

often i'm sure. and they tend to leave door open about 3 to 5 inches. they have curtin and told owner not for any reason let them leave door open. but i'm sure it happens.

[sandpipertech]

Theres more to this story...

Also sounds like you are oil logging in the evap need to force it back into condenser and you also need some kind of low ambient controls on this unit and absolutly need to be on pumpdown set up with defrost timer...

Why would i be oil logging in the evap?
I agree that it may need a defrost control but it hasn't in 6 years....and they have had it at the same temp the whole time...

[jaybee]

Oh... Didn't read no defrost timer. Interesting

hmm

[skpkey9]

Easy low ambient, pressures fall low enough to where there not enough velocity to return oil causes lower few inches of coil to Ice up, same thing if the coil is iced up and its also unknown if there is a p- trap installed , also tell tale sign of oil logging is the lower portion of evap icing and not the rest if infiltration or door being left open top half of coil would be icing up and if it were a defrost issue the entire evap coil would be icing up...

Hope this helps....

[sandpipertech]

Good call skp.
No oil trap installed.
Cond. is on roof above evap.

Why would oil logging in bottom of evap be the cause of frosting? WOuld it just ask as an insulator? Causing bottom of coil to be inefficient at picking up heat, causing coil to run cold.

[hvac wiz 79]

ive never experienced oil logging .. that's interesting to know though because while reading OP I was thinking something more along the lines of it being in relation to the TEV .. like a partial restriction from a fouled up inlet screen or trash in the valve

[sandpipertech]

ive never experienced oil logging .. that's interesting to know though because while reading OP I was thinking something more along the lines of it being in relation to the TEV .. like a partial restriction from a fouled up inlet screen or trash in the valve

Now THAT is what i was hoping somebody would say. Thats what ive been thinking....

[skpkey9]

sandpipertech - basically yes...


hvac wiz 33 - that would cause a whole new and different set of issues...

[ZeroTolerance]

Good to know skp. Didn't think of that and probably never would have :P

[kevincompass]

could it be unequal circuit loading due to a dirty evaporator making the bottom of the coil to get less airflow then the top

[skpkey9]

Disable you condenser fans and heat up your TEV bulb to open valves and the higher pressures will force oil back into compressor, check levels on compresor sightglass if any to ensure you now don't have to much oil in system ( ie from compressor change out if any were done ) , if you do adjust accordingly. now that you have moved oil back where it belongs . Now its time to make the necessery repairs to prevent this from happening again...

Hope this helps...